cafe guide

Cafes, Bobbers, Scramblers and Flat-Trackers and Ratbikes: Jim's Guide To Upgrading Cheap Old Rice Rides. By Jim March – draft 1.0, May 3rd 2013 INTRO...

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Cafes, Bobbers, Scramblers and Flat-Trackers and Ratbikes: Jim's Guide To Upgrading Cheap Old Rice Rides. By Jim March – draft 1.0, May 3rd 2013 INTRO

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WHAT ARE WE TRYING TO ACCOMPLISH HERE?

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HANDLING THEORY AND PRACTICE

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Front end mods:

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Rear end mods:

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The Book Of Rims

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Overall right height notes – front and rear as they interact

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ERGONOMICS MODS

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ENGINE MODS AND SELECTION

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Engine Modifications

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Pipe Mods

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Carb Options And Tuning

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Carb Rebuilding: CV Carbs

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Carb Rebuilding – Roundslide carbs

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Carb Tuning

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WHAT BIKE TO START WITH?

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SOURCES (list of suppliers online)

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HOW TO PILOT A CAFE RACER

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IF YOU FIND THIS USEFUL, consider tipping the author ($5 or ???) at my wepay account: https://www.wepay.com/donations/cafe-builder-s-guide-donation-jar The listed manufacturers and sellers did NOT pay me to get in here, nor will I ever charge for listings. If anybody has more tips of any sort including cool suppliers, drop me a line:[email protected] If I make a bit on this thing I will be more likely to keep it up to date :). But honestly, this started out as my own notes for my own upcoming next build and that will remain part of the thing as I progress.

INTRO This is for somebody who wants something different. Instead of buying a fairly modern beginner sportbike like a Suzuki SV650, you want to take something older and upgrade it to personal taste. Or you've already got something older and want to tune it up on a budget. I'm writing this to give you a guide to how to it safely and with a minimum of mis-steps. This guide will use the “Cafe Racer look” as a starting point, and the info in that will valuable to anybody going a different direction such as a Bobber or Scrambler/Flat-tracker (the latter two more or less the same thing). WHAT ARE WE TRYING TO ACCOMPLISH HERE? “Success” in building a rat-cafe (“on the cheap”) means building a bike that is light, fast-handling and on a TIGHT twisty mountain road can keep up with more or less anything on the planet, with a good enough pilot at the wheel. On a very tight road the horsepower advantage the other guy on some modern sportbike can't be used against you very well. You'll have one advantage, and it's not a big one: your lighter bike with lighter rims and tires will be able to flop over into a full battle lean faster than anything this side of a high-bucks Ducati or the like. It's not a huge advantage but on the right road it's enough to embarrass the hell out of some newbie squid :). And you don't need to pass 'em on a rat cafe, just keep up and drive 'em bonkers. Huge fun. Here's what success looks like: Price: under $3,000 max. If you're spending more than that you're doing it wrong in my opinion. Rims are as light as you can get 'em. This is crucial to a really good performing canyon racer cafe ride. We'll talk about those in their own chapter. Carbs should be either well-tuned factory type (usually CV although we're going to do a whole chapter on carbs!) or better yet some sort of roundslide or flatslide. For smaller to average size riders, most folks will be happy with a twin of 350-500cc or a 500 to 650 single cylinder, and around 35 to 50hp. Bigger pilots might want to get up to the 65-75hp range in either one of the bigger twins or possibly a 4-banger motor of 650 or 750cc (meaning a classic air-cooled four as opposed to a modern water-cooled “supersport” motor). Cosmetically, on the next page there are some classic '60s Britbikes that most cafe builders are basically aiming at, or check out this video for more info on the cafe scene in general: http://www.youtube.com/watch?v=vmAaVgUzNh8 Most of what's on that video, and what we're talking about in this guide, is “fakes” of those early British cafe racers made out of 1970s/80s/90s/whatever Japanese bikes...or whatever other weird stuff you can scrounge up. :) Don't assume there's “rules” here...

They all have certain things in common: they're twins (although British singles were popular too – go do a google image search for a Honda GB500 as it's a pretty close quasi-replica) and they have large light rims involving aluminum-hoops-over-spoke in a distinctive “H-pattern” that looks “flat-faced” on the outside edge (also known as “shouldered” - all of these rims pictured above are of that sort. These rims are light and stiff and remain the lightest street rims and tires you can run without going to carbon fiber $5k-a-piece monsters. Put another way, there are five aspects to a low-bucks cafe build: 1) Looks (which I'm not even going to talk about, that's on you!) 2) Engine performance.

3) Suspension and handling – and we'll file “dumping excess weight” in there too as being 5th . 4) Ergonomics – seat, handlebar and footpet positioning. Of these I consider suspension and handling the most important, ergonomics second, engine third, looks in dead last :). But that's me. Some things affect more than one issue – exhaust mods can increase cornering clearance (handling issue) while dropping total weight (sometimes by a lot) and can also increase performance when done right. I'm going to take you through modding each area before we talk about bikes, so that you have a good feel for the theory as to why you would want any one particular bike as a starting point. HANDLING THEORY AND PRACTICE In a corner your tires are going to bounce over small bumps. You do not want the tires “catching air” in any fashion during those mid-corner bumps because when that happens you tend to “chatter sideways”. The tires lift, get thrown sidesways (in mid-corner remember), and on landing there's a risk they won't hook back up again in which case you and the bike could be seriously dented. First key to preventing this sequence is low rim weight. It is impossible to overstate how vital this is. Light rims and tires will not have as much upward momentum on those mid-corner bumps, and it will be easier for the suspension to push the tires back down onto the road when they try and lift. In other words, lighter rims and tires will allow crappier suspension parts to still work OK. Therefore dropping the rim weight and running narrow-ish tires is a “universal upgrade” to the entire suspension process. Second advantage with light rims is that there's less gyroscopic effect holding you upright. This means you can flop the bike over faster into a corner, perhaps out-diving somebody in a much bigger, more powerful bike (with heavier wider rims). It's hard for somebody in a supersport to use their massive power advantage if – surprise! - you already have the inside line on their dumb butts :). When we get to specific bike options we'll talk about possible rim choices for those bikes. (Tidbit though: Honda “Comstar” rims rock hard...they look like crap but they're stiff and light, the best rims of the late 1970s through early '80s.) Front end mods: Well one option is to swap out the whole front end, triple trees, forks, brakes, rims, the works. Junkyard bits (or somebody's total scrap “dead engine” parts bike) can often be had cheap with effective scrounging. Ebay is often worth looking at. A total front end swap is often worth thinking about if your original forks are fairly thin, esp. in the 35mm width range or less. At 37mm or 39mm you're doing better. To do Frankenbike front ends, first you need to know about the fork diameters of various bikes to figure out which bikes are an upgrade from the diameter your have now. There's data at: http://www.dotheton.com/forum/index.php?topic=20950.0 If you want to keep your original rims (instead of keeping the one from the donor source) you need to know about axle diameters:

http://www.dotheton.com/forum/index.php?topic=20952.0 And then there's these guys, who sell “adapter steering head bearings” for swaps: http://www.allballsracing.com/index.php/forkconversion Here's the kicker: you punch in what your core bike is (meaning the frame) by make/model/year and it will list which potential front-end donor bikes they have adapter kits for, along with their adapter part number. This eliminates a lot of guesswork! Other possible mods to the front end are: * Fork braces. These can be downright vital if you pull off the front fender, because the original steel front fender on typical cafe conversion bikes act as factory fork braces. Superbrace is the top source: http://www.superbrace.com/ - these stabilize the entire front end, reducing “headshake” tendencies by keeping everything properly aligned. Highly recommended. * Cartridge Emulators. OK...stock cafe-project front ends usually use old-school fork damping. There's a plate that moves up and down with the forks with holes in it, which is going up and down in a pool of oil. The ability for oil to flow through those holes is what slows down the fork's movement even more than the springs. With modern “cartridge” sportbike forks, there's still holes but they have little flapper “spring plates” over them. This lets them pass less oil on a small bump but more on a big bump – in other words, variable damping. Remember that mid-corner bump problem? Yeah, well this is a big part fo a complete solution to that issue. Cartridge emulators are replacement “hole assembly” units that screw into classic forks and adds modern variable damping. The result is invisible so if you're going for the “classic look” (instead of grafting on GSXR forks or whatever) they rock. Racetech is the top name but there's others – google “cartridge emulators” for more: http://www.racetech.com/HTML_FILES/EMULATORGV.HTML Pro tip: if you're looking for a front end swap, you might check here to see if your donor bike forks are supported by racetech or other makes of cartridge emulator kits. * Progressive springs: another upgrade for classic fork tubes, progressive springs have an area of “wide springs” for stiffness and tighter-wound for handling small bumps. Just google “progressive fork springs” for your bike...they are widely available. * El Cheapo Fork Preload Mods: increasing the spring stiffness in your front end can help under some circumstances, if it “feels too soft” out there. OK, fine – take the weight off the front end, frame on a milk crate will do, or hang the handlebars with ropes. Take the top caps off each fork tube and cram 1” long sections of the appropriate width heavy PVC pipe from any good hardware store down in there, re-cap. Try it out, vary the preload as needed with different lengths of PVC pipe. Dirt cheap and invisible mod. Make sure you clean up any plastic fragments that might flake off in there!!! Rear end mods: * Make sure the swingarm is not loose!!! Get the weight off the rear, pull the rear rim, disconnect the shocks so that the swingarm is only on there via the front. Now wiggle it. There

should be minimal side to side yet smooth up and down. If it feels at all wonky swap the bushings. Listen carefully here: stability at that swingarm joint is beyond “vital”. Instability here is seriously, radically unsafe. * The main upgrade available at the rear end is shocks. Most of these bikes will be dual-shock and that can work OK. You want, yet again, progressive springs – in this case it usually means there's two actual springs, one wound tighter than the other. Pictured is an example of a very good rear shock – progressive winding (note the dual-rate single spring) and an external oil reservoir – more oil available means the oil stays cooler longer. (Really only vital in race applications or if you're a major canyon racer.) Shocks can be ordered “over-length” if you want to “jack up” the rear so as to increase cornering clearance. But there's another, even more vital feature not immediately visible: the best shocks can be ordered set up for your specific bike and pilot weight. At that point you're spending $600 or more from Works Performance or the like, but the results...well, they can be downright awesome. On a budget? The cheaper non-reservoir rear shocks from Dime City Cycles or the like that are still progressively wound (often using two different actual springs stacked one on top of the other) for under $200 can work very well if you adjust the preload properly and run light rims. (See “sources” at the end for Dime City's website and much more.) * For those with access to a welder and guts, conversions to monoshock can be damned interesting because you can then sometimes use junkyard rear shock units from modern sportbikes, which can be surprisingly cheap for what you're getting. A few potential cafe projects start out as monoshock already, mainly the early Yamaha Viragos and the Honda GL650. The Book Of Rims For best results as a cafe you want a 19” front rim, 18” rear. That's “optimal”. You also want the front and rear diameters of each to be a fairly close match – 19” front and 16” rear is not advisable. 18” front with an 18” or 17” rear can work or a 17” rear 19” front if you can fit a 140-80/17 on it. You also want the rims to be as light as possible. The best possible setup is aluminum hoops over spokes. These will be much lighter than any modern sportbike rim this side of expensive carbon fiber or the like, and with less gyroscopic effect you'll be able to flop it over into a corner faster than anything else on the street. Steel hoops over spokes will be OK and you can upgrade later – Mike's XS has aluminum rims in stock with spokes in 36spoke and 48spoke. There was a factory option on some 1970s-era Yamaha XS650s - “H-pattern” (or “shouldered”) factory aluminum-over-spoke hoops. They're hard to find but if you see them snatch them up. This is also the preferred type if buying replacement hoops from Mikes...see this page for examples: http://www.mikesxs.net/products-56.html#products Where possible avoid the “quasi-cruiser” variants of these bikes, usually with 16” rear rims. Also: most factory “mag” rims of the pre-1985 period were disgustingly heavy, esp. Yamaha but also Kawi and Suzuki. Honda however got it right with the “Comstar” aluminum rims – they were very light and rigid, excellent rims from the “narrow rim” period. Honda mostly used these from 1978-1982. The

early Honda Goldwings (GL1000) from 1975-79 had two rim options: Comstars by 1978 forward and before that (and as an option all years) excellent “H-pattern” (also known as “shouldered”) aluminum-over-spoke rims front and rear. They were 17” rear, 19” front although you could of course lace up different rims. I am told there have been some successes grafting this rear rim/hub (along with a disk brake upgrade) to the CX/GL500/650 twin series, in particular the GL650 that I know of. Apparantly that early Goldwing rim (and possibly the Goldwing rear drive unit on the GL650 swingarm?) can bolt right in with minimal mods. I have not personally tried it yet but the guys on the CX500 forums are saying it's a “go”. You can do OK with 16” rear rims but you'll want an 18” or 19” front. Smaller 16” fronts from the earliest period (notably the Yamaha Radian600, earliest Kawi EX/Ninja 500 and some others) had squirrelly handling. If you're buying a bike with steel hoops over spokes and planning on swapping to aluminum hoops later, yeah, that's doable...figure you'll have to replace the “nuts” at the end of each spoke but usually you can recycle the original spokes, which will be an easy way to match up your hubs to the new aluminum hoops of the same diameter. BUT! Go count your spokes and make sure either Mike's XS or Dime City Cycles (see links section, end of this document) has aluminum hoops in your spoke count, otherwise you'll be paying bigger bucks at Buchannon's Spokes for aluminum rims with custom-drilled hole counts to match a particular bike's oddball hub pattern. Fortunately Buchannon's can also sell you the correct spoke lengths for your hub with whatever size rim you want. http://www.buchananspokes.net There are also a bunch of good guides on how to lace up a custom rim and hub all over youtube if you search on terms like “lacing rims custom” or the like. CHAIN DRIVE BIKES ONLY: swapping rims between very different models or even brands is often workable, so long as the axle diameter is right, the chain type matches the sprockets front and rear and you might have to tweak the width of one of the spacers on a grinder. A list of which bikes use which axle diameters is at: http://www.dotheton.com/forum/index.php?topic=20952.0 – make sure you grab the axles, axle nuts and spacers from the donor bike to ensure an easy hack job, OK? Also, swaps are easier on drum rear brake setups, in general. Overall right height notes – front and rear as they interact Jacked up is good, within limits. There are however things you need to know. SAFETY WARNING: The closer the forks point to straight down, the less stable they'll be. Got that? Now, that can be OK if you've also done “stability enhancement mods” to the front such as a fork brace and/or thicker fork tubes...plus make sure the swingarm pivot point isn't sloppy as that will affect FRONT end stability. So. If you've taken steps to stabilize the front, you can then risk jacking up the rear to gain cornering clearance, or if you're a smaller rider and don't need as much clearance, you can drop the forks in the fork tubes to lower the front end and point the forks closer to straight down. Pictured is a set of fork tubes slid up within the triple trees, dropping the bike and speeding up the steering...he loosened the two nuts shown

plus two more like them below, slid the fork tubes about an inch, tightened it all down. Even half an inch can have major effects on the steering feel and front end stability. Either way, steeper fork angles make the steering quicker (“twitchier”) which can be a good thing in capable hands. This kind of mod is not for newbie pilots!!! Capische? You can however work your way up to this point as you mod the bike if you're new to motorcycles in general. Obviously, front fork complete swaps can also affect the length of the front end and hence the angle of the fork tubes – take all that into consideration when swapping front end. If the donor forks are longer than stock, obviously moving them up the triple trees some to restore the stock angles is safe. Do not learn that your front end is unstable in a speed-wobble that kills you. You have been warned! M'kay? And for God's sake, at the first sign of a speed-wobble that you pull out of, plan your next set of mods to stabilize the front some more – fast. Or take off that swoopy long rear shock you just bolted in and put the shorter stock units back on until your shiny new fork brace or other nice front end mods come in. Whatever you do as a bike modder, listen REAL WELL to what the bike tells you. This is the most important thing I've said in this entire document. ERGONOMICS MODS This is a very personal area so I'm not going to say much. Run the handlebars you want, standard or clip-on type. Worst case you'll make the comfort stink for long distance, if so swap around. I would recommend starting with low “flat track” type bars available at any bike junkyard for $10...run those, see if you like 'em, swap later once the bike is closer to “done” (ha!). Seat is the same deal: run whatever you like, don't be afraid to roll your own. On a budget? Rolls of closed-cell camping mattress foam, some contact cement to tack it down, a knife to shave the stack to shape and a $15 duffel bag from a sporting goods store can build you a surprisingly good seat. Yeah. Duffel bag...I said it :). Very minimal stitching needed to turn that into an awesome seat cover. One thing on seats and handlebars that may be of interest to folks driving long distances: learn to set your “freeway float”. While leaning forward at, say, 75mph, you can adjust your seating position and esp. handlebars so that there's almost no weight on your arms as the wind literally holds you up – you're “floating”. On a forward-lean bike (cafe or sportbike) with no windscreen, this is a top secret of a comfortable long-distance ride. That and a full-face helmet. :) With rearset footpegs...there's something interesting there: >>The closer you can mount them to the rear swingarm pivot point, the better.<< Because that's the part of the bike you want to stabilize with your feet. Dime City, Mike's XS and Lossa have rearsets – all are listed under “Suppliers” at the end of this article. Hardware stores have good selections of threaded rod and various bits to make linkages out of.

ENGINE MODS AND SELECTION Let's start with selection of the core bike with motor. You should care about horsepower. No question. But you should also care about “how it makes the power”. You should NOT care much about CCs (cubic centimeters of displacement, which is where we get “500cc” or the like) as a motor size as it borders on meaningless. A motor can be “peaky and explosive” with major horsepower for it's size, or it can be “torquey and controllable” for it's size. Or somewhere in between. The factors that make a bike put out big power in a less controlled fashion: 1) More cylinders for the size...a 600cc 4-cylinder modern sportbike motor (CBR600RR or the like) could easily put out 110hp stock. A Suzuki “Savage” (aka “S40”) is a 650cc single cylinder, “bigger” than the Honda by 50cc, but it's only putting out about 35hp. 2) Air-cooled will mean less peak power than water-cooled, all else being equal. It's not definitive but air-cooling is a sign of a less “frantic” motor. 3) More valves per cylinder means big peaky power, all else being equal. 4) High redline means big power. 5) Two-stroke motors will put out more power for their displacement than a four-stroke. They are also less reliable. Unless you really know what you're getting into, avoid two-stroke motors like the plague. (The breed is now basically extinct because they put out severe pollution...but back in the 1970s they were still a thing...) You can of course plan out a cafe for a serious, experienced rider. You can start with a bike that has a supersport-class modern motor if you want. There's no rules here. But a newbie rider should consider a twin with a max of 50-65hp (the latter for a large rider) as opposed to a 4-banger hypersport with 100+ ponies on tap, unless you SERIOUSLY mod the frame and suspension to fully modern standards. Engine Modifications The only mods a beginning cafe builder should need or want is mods to the intake and exhaust. Done right these won't kill the engine. Using the extra power you get (if you do it right) with heavy-handed throttle can of course wear the motor out faster. Pipe mods Generally you want to run the stock inside width on your pipes, and do a “merge pipe” on twins, triples or fours. (WARNING: a lot of stock pipes are double-walled so if you measure the outside diameter, the inside diameter (that matters in terms of the width of new pipe you're doing) will be way off. A “merged pipe” means all the outputs merge to one point at a set point downrange, and then you run one muffler. This both increases performances and saves weight (one muffler is lighter than 2 to 4).

Here's why there's a performance boost: Take the case of a twin (two-cylinder). Set up right, when the exhaust pulse from one cylinder hits the merge point, the pulse from the other cylinder is just starting. Once past the merge point the first cylinder's pulse literally pulls the pulse from the other cylinder. And when that one clears the merge, the cycle starts again. Same with triples and four-bangers. If you are doing a fully custom exhaust you can find out where the proper merge point is by taking measurements of the merge junction distance from the heads on a professionally built aftermarket pipe and then copying that distance. Other factors: if you run fatter-than-stock pipes, your low-RPM power will suffer but your upper-RPM power can increase if you do everything else right. However, you probably need a seriously improved motor to take full effect of fat pipes – bigger pistons in bigger cylinder bores, headwork, hot cam, the sort of things that are beyond the scope of this guide and have to be specific for your motor. Doing a full custom exhaust on a two-cylinder bike isn't as difficult as you might think. Even on a four-banger it can be done for reasonably cheap. Dime City and Mikes' XS have “generic pipe kits” with various bends and straight bits that can be welded up: http://www.mikesxs.net/product/19-0420.html http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycleparts-biltwell-universal-exhaust-kit-ex-aa-rw-00-0.html These kinds of kits should work fine with most 1970s-era twins from 350cc up through 750-800 plus many of the bigger singles (500-650). You can use stubs of the existing stock pipes at the heads as a starting point. Local auto muffler shops are often willing to help for surprisingly cheap – avoid the national chains, go with a little mom'n'pop local type, they're often very cool. For a merge point, one option is to cruise bike junkyards looking for a good merge point from an otherwise wrecked set of pipes. $10 and it's yours, cut out the merge point, use it in your otherwise custom setup. The results will look like crap but run great – thank the diety of your choice for the pipe wrap tape look . Now, one reason to do all this is that it is sometimes the only way to get the pipes fully and completely out of the way of your lean angle. And for handling issues, that matters. In the pipe shown here, the pipes interfere with max lean angle on a right-hand turn, which isn't good. If the footpegs were up higher and further back (“rearsets”) the difference in available cornering clearance would be even more obvious. That pipe should be tucked in under the engine like Eric Buell loves to do instead of hanging off of one side. The other way to get pipes out of the way is to run them high and off the side in “Scrambler fashion” or if you've dumped the original carb airbox, lose the side covers too and run the pipes out the underside of the seat for a very effective and cool look.

As to the muffler: I am a huge fan of using generic-catalog Supertrapp exhausts. Here's why: with the ability to add and remove baffle disks you get the chance to tune exactly how much air the pipe is flowing. This is extremely useful when doing performance tuning, in large part because instead of re-jetting the carbs to exactly match the pipe, you can get the carbs close and then match the pipe to the carbs. It is impossible to overstate how much easier this can be. Summit Racing is a CAR supply place that has a ton of available Supertrapp muffler ends for various diameter exhaust pipes: http://www.summitracing.com/search/brand/supertrapp/product-line/supertrapp-s-c-standard-mufflers? autoview=SKU – as you can see, this series goes all the way down to a 2” inlet size. If your outlet is smaller than that, no problem, any muffler shop should have tube expanders to take the end of a 1.75” or whatever pipe up to 2” in seconds. If this link stops working just search “supertrapp” no quotes on the Summit website like so: http://www.summitracing.com/search/brand/supertrapp – they have cool little “shorty” units and whatever else you want. Also a fair number of hanger brackets. You can also go to Dime City, Lossa or the like and get all kinds of different bike mufflers. OR junkyards are your friends of course! But I'm telling you now, the Supertrapp option completely rocks if you have the cash available. Carb Options And Tuning OK. This is the big issue, in my book. Bike carbs of the 1960s and early '70s were all “roundslide” type direct-actuation carbs with a few rare exceptions...BMW for example went to CV-type carbs early on. CV carbs, in my opinion, stink. They're delicate, hard to tune and cannot produce as much power as a good direct-actuation roundslide or flatslide. Let me show you what I mean.

There's some bits left out – the secondary pilot jet, the low-speed idle jet and the system for dropping new gas into the reservoir. I've also left out the small air passages that forces the CV slide to rise. (There are also some variations on exactly how the slide is controlled in some roundslide and flatslide designs but this doesn't affect how they perform.) But this simplified view is enough to understand why these carbs are different. The CV carb has tiny advantages where fuel economy is concerned and a modest decrease in pollution that allowed the Jap makers to avoid having to go to catalytic exhausts. To be fair, the CV carb does have one performance advantage: as the engine speed rises it always gives the engine just the amount of gas it needs – never too much. This would be great except it doesn't do so very quickly! And since there's two different things in the carb's bore getting in the way of airflow (the butterfly valve and the main slide) there's less total airflow, which is why you can replace a 38mm bore CV carb with a 34mm roundslide and still get a performance increase. On the roundslide (and racing flatslides) you get direct no-BS control over the main slide. You want it up? Yessir, right frackin' now, here we go, hang on tight. Now, that means that if the carb is a bit on the big side, you can “bog” the motor feeding it too much gas. But even if that's an issue, you can still learn to “ride the throttle” on the way up the RPM scale. A really properly tuned roundslide won't do that so long as you didn't pick too big a carb. I made a mistake many moons ago with my XS650, went for 36mm roundslides when 34mm is the better answer and I ran into that bog situation...but even then it was a short learning curve and the top end power was completely kick-ass awesome so I didn't worry about it. Now. One more difference – the roundslide (and flatslide) doesn't care much about the incoming air flow quality. It just sucks it all up and begs for more. Obviously, obstructed airflow is no good and some of the cheaper “pod air filters” do that. And velocity stacks of some sort do help. But overall the roundslide/flatslide types don't care much about the type of air filter setup you run – or no filter at all and they'll still work OK. CV carbs are extremely picky. That incoming airflow has to be correct and straight, plus for reasons I still don't understand they need some sort of “air box” on multi-cylinder multi-carb bikes. So when you see “pod filters” of any sort on CV carbs, well...flat-out, that ain't right. You CAN sometimes make 'em “mostly work”, sometimes if you're a real master at tuning them you can get them almost running as good as stock. Almost. More likely you'll have all kinds of stumbles in the power output as it climbs and top end power will be limited. So, assuming you're not yet ready to design a new roundslide or flatslide carb setup for a given bike, how do you do the conversion? Well you find out if anybody has a pre-built kit, OR you look for a bike old enough that it used roundslides as the original factory carbs. Or if there's no packaged upgrade kit, search around that bike's forums and see if anybody has successfully added better carbs and if they left decent notes on mounting options, jetting recipes, etc. Mikuni VM (usually VM34) carb kits for

the XS650 are easy to get from Sudco and http://www.650central.com/ - the latter for about $450 which is reasonable. User MurrayF on the CX500 forums has a VM34 kit for the CX/GL 500 and 650 motors, with fully custom manifolds needed for those bikes: http://cx500forum.com Mike's XS has a cheap flatslide kit for the XS650 (at $300) but I've heard the quality is iffy as the carbs are out of China instead of Japan and the castings are...meh. Lossa has you covered for Honda twins, Sudco supports the EX500 mini-sportbike and the Vulcan 500 is similar enough they should fit there too. Most of the Honda “SOHC” (Single OverHead Cam) 500, 550 and 750 motors had roundslide carbs. I have heard of some successes grafting used sets of those onto later DOHC (1979 forward) CB750s but I don't know the details. Carb Rebuilding: CV Carbs The main downside to older CV carbs (esp. 20+ years old) is that the “diaphragm” on top can easily crystalize and develop cracks or tears. Once that happens the carbs will turn useless. To check, pull off the “mushroom cap” thing on top CAREFULLY and check those rubber sheets. If you need new diaphragms this outfit may have you covered: http://jbmindustries.com – note the link at the top right. Once you have the top of the carb open and have checked or replaced the diaphragm, carefully make sure the central slide moves up and down smoothly. Once it does re-cap the “mushroom top” to protect the diaphragm and only then flip it over and check/clean the bottom end. The rest of the carbs are easier. Once you know that the top end is OK, screw it back down, turn it over and start taking it apart and cleaning it from the bottom. Pull the fuel reservior bowls, take everything apart, blast out all the little passages and removable brass gas-flow inserts (“jets”) with compressed air. No air compressor? Fine, go to an office supply place and get a couple of $5 or less cans of “compressed air for computer cleaning” like what's shown here. You want those little plastic nozzle extenders, they completely rock for cleaning carbs. I think they actually work better than an air compressor and seem to clean old gas off with nothing else in the way of solvents needed! Make sure you get the gunk out of the reservoir (aka “float bowl”) and whatever you do, write down the numbers stamped on each of the little brass inserts that meter the gas, known as “jets”. When you tune the jetting later (if you need to) you'll need to know which jet sizes to order to go up or down from where you're at now on the main and pilot jets. Surprisingly, the rest of the insides of the carbs will usually be OK. They'll need cleaning but otherwise you don't usually need the sort of “carb rebuild kit” that comes with new gaskets, new small rubber bits, etc. Do one carb at a time!!! That way you don't mix up “innards” from multiple carbs :). Carb Rebuilding – Roundslide carbs Same as the CV rules above except you don't need to check the diaphragms because there ain't none.

Carb Tuning There are two issues here: jetting and synchronization. You “sync the carbs” by making sure they flow the same amount of air, each. There's a couple of ways. With roundslide carbs you can set the amount of “starting point height” of each slide by gently measuring to make sure all the openings are the same width with the blunt ends of drill bits. Drill bits come in packs that are very precisely measured, so with the carbs in the bike or better yet off (“bench synchronization”) you match up the slide heights by measuring the gaps below the slides with drill bits. Match them all up to the lowest one, try it out, too low, match them all up to the next size up bit. It is more precise to measure the flow from each carb with a suction tester while the engine is running. There are numerous youtube videos on how to do this for each motorcycle...search on the make/model of your bike along with “sync” or “synchronize” and “carbs”. You can also find plans on making a homebrew synchronization meter or you can buy meters for two-cylinder bikes for less than $50 at Dime City or elsewhere. Jetting is more complex. Do a spark plug check with brand new plugs to see where you're at: http://www.4strokes.com/tech/sparkplg.asp When you cleaned/rebuilt your carbs you wrote down your jets, right? So you can now order the next size (or two sizes) up and down in each direction on the main and pilot jets pretty cheap, and start testing them. Jets are available at a bunch of sources online; you'll need to know either the make/model of carb you've got OR if you know your carbs are stock for your bike, the make/model of bike. A lot of motorcycle shops have trays full of jets laying around for $3-$5 a pop. Finally, if you went with my Supertrapp exhaust suggestion you can “re-jet” by adding baffle disks (leaning the bike out) or removing some (making it richer and quieter). This can let you get it running right now, then go score bigger jets later, swap and add some disks to match up for more oomph. WHAT BIKE TO START WITH? Rule one: don't do a 2-stroke. OK? Seriously. Don't. Not real reliable long-term, parts are getting scarce, and if you mod them wrong you'll get horribly peaky power that only an expert pilot should be anywhere near. With rare exceptions (such as the Yamaha TZ250/350 series as Canadian or other such grey-market imports after 1980ish) most had horrible suspensions and frames. Put another way: if you're getting valuable data from this document, don't go 2-stroke. If all this is old hat to you, maybe you're ready for the mechanical annoyances :). Past that, you want something fairly common and then make it uncommon yourself. You want something with a ton of junkyard parts available and if possible some aftermarket support. Going with something obscure will hurt you unless you're willing to really dig around for parts. (BUT, Ebay is making finding obscure parts easier so...if you think you know what you're doing...). I've already discussed HOW different engines make power. So let's assume we're going “classic”, with a bike that started life in the 1970s or '80s (or at least, is that kind of tech level). Bigger rider recipe is to aim for about 60 to 70hp and under 400lbs – under 350 preferred. Easiest

starting points are a Honda CB550 4-banger or the equivalent Suzuki or Kawasaki 550s, 650 max although most are going to be too heavy, Yamaha XS650, a well-tuned Yamaha Virago 750 or 920 (early era monoshock types!) and possibly the earliest Honda Shadow. There's also the Yamaha Seca 550 and a bit later the Radian 600, although the handling on the latter is kinda squirrelly it can be fixed if you can find a cherry specimen cheap enough. The XS650s are unfortunately all ate up by people doing cafes, bobbers etc. because the engine is both very good and a very close cosmetic replica of a classic 1960s British twin...and unmolested examples are big money. The Radian600 motor was later bolted into the Seca2-600...the only 1990s-era 4-banger 600 that was still “newbie friendly” well into the 1990s and as they're turning up cheap enough, a possible candidate for a “modern looking cafe”. Smaller riders can have a lot of fun in the 40-45hp range and 350lbs, 300 preferred. You can get there with one of the Honda 400 or even 350 four-bangers if you can find one, the various Honda/Suzuki/Kawasaki 450 twins of the 1970s through mid-80s, or some people have a lot of fun taking the biggest single-cylinder street/dirt enduros they can find and converting them to a cafe/supermotard mutant hybrid. Yamaha actually did a factory version at one point called the SRX600 and Honda had the GB500 – both are rare and worth big money but show what can be done with an early 1980s big single dirtbike such as the Yamaha XT500/550 and Honda XL500-600 types. Weirdest of all is the Suzuki “Savage” 650 single which believe it or not can be rigged as a Cafe even without a pre-built “kit” which is available: http://www.youtube.com/watch?v=D5r6rhQiT-k Some people like the Honda CX500 as a starting point...honestly, it has issues with being top-heavy and does a little bit of weird “rolling” when you hammer the throttle in mid-corner so...hmmm...for a really serious effort, not a top choice although it can be a lot of fun for a less gonzo effort. There is also the CX650/GL650 variants made in one year only, 1983, that put out about 15hp more than the 500 stock and has potential as a “bigger guy” variant. You can also shoehorn the 650 motors into 500 frames, and a lot of people are doing that. There's a user by the name of MurrayF on the forums at http://cx500forum.com who has developed a complete kit to bolt a pair of Mikuni VM34 carbs onto all of these bikes, 500 and 650. He also sells pre-fabbed front motor mount hangars to allow dropping the 650 motors cleanly into 500 frames and is otherwise THE go-to guy on these bikes. The VM34 kit with new intake runners, throttle cables and everything else needed is $500 I think. You can order them for a 500 motor and he'll sell you jetting later for $20 if you upgrade motors (or switch entire bikes). It's high for a dual-VM34 kit but considering he had to design all-new intakes to avoid the carbs hitting the gas tanks on these things it's fair...and there's lots of reports that he has the jetting recipe extremely well developed. There is also a guy selling parts to convert CX-series Comstar rims to spokes: http://motosynthesis.blogspot.com/p/shopping-cart.html – at the prices he charges I would do the rear only, match it to a spoke front rim from a Honda GL1000 (early Goldwing). I'm also told the early Goldwing rear 17” stock rims can be grafted onto the GL/CX 650 shaft drive units but have not confirmed this personally. Kawasaki had a 750 twin to compete with the XS650 but it has the drawback of being very rare plus the Kawi was heavier and worse handling. Kawi frames throughout most of the 1970s had the worst rep for flex. The Kawi 550-4banger wasn't terrible but it needed upgrades to the suspension. The Kawasaki, Suzuki and Honda 650 and 750 four-bangers of the late 1970s through early 1980s are worth looking at for the biggest riders, mostly. They're going to be harder to get good handling out of for pure weight reasons. I'm 6'4” and 300lbs, and I had a lot of fun many years ago on a tricked-out Yamaha XS650 twin. Now I'm going to look for something a hair bigger, but not to a 750 4cylinder. I am NOT a fan of the XS750/850 triples for a number of reasons. The power to weight ratio is iffy, the

shaft unit is heavy and the options for a lightweight rear rim are non-existant. There is a rare variant of the early Yamaha Virago 920s that you might want to keep an eye out for: the XV920J with a chain drive, also known as the “Eurosport Special”. Awesome cafe starting point. Overall, the Yamaha XS650 has the most going for it for a number of reasons. The power output for this era of frame tech is a near-perfect match. It looks a lot like a late-1960s Britbike. Aftermarket support is awesome including big-bore engine kits of 750 or more if you want to go nuts. The usual advice is “avoid shaft drive” but...that's not always the case. The very earliest first-generation Yamaha Virago 750/920 have a lot of interesting potential. Even the 2nd gen with more chrome can be stripped down – the easy way to ID these early ones is the monoshock. There's no frame under the motor at all – the motor IS the lower frame. Actually makes it damned easy to work on :). Finding or building lightweight rims for the Viragos can be a pain. The stock cast rims were heavy. You can however swap in spoke rims from later “Harley looking” Virago variants and re-spoke those hubs on aluminum rims. And the CX/GL 500/650 Hondas are designed from the ground up as shafties with the motor pointing the power the right way so there's less “shaft drive power loss”. Anything bigger than 750 from the early 1980s or prior is going to be a giant pig of a bike :). This includes the Yamaha shaft-drive 1100s, the early Goldwings, etc. The only possible exception is the Honda CB900 and CB900F – try and avoid the CB900c (“Custom”) despite it's bizarre 10-gear double-tranny setup. And past about 75hp, you really need a more modern frame and suspension! There are also some early Japanese V-twin “Cruisers” that may have potential as cafes. The earliest Honda Shadow 750 and 800 motors had 66+ horsepower and were fairly light and narrow. Suzuki's Intruder 700, 750 and 800 (original, not “Volusia”) and the Kawi Vulcan 750 were similar. The Intruder already comes with light aluminum rims but the rear of the shaft drive unit is particularly heavy. Light rims on the Shadows are possible if you can find a Shadow 800 (1988) spoke rear rim and re-spoke it to a 17” or 18” aluminum-over-spoke rim setup. The Kawi has the worst rim options and the motor is a wee bit delicate for my tastes. There is also the Kawi Vulcan 500 or earlier LTD454 twins that have potential as cafes; they share engine similarities with the EX500 small twin sportbikes.

SOURCES Dime City is the biggest “general merchant” of Cafe parts online. Good folks: http://www.dimecitycycles.com Lossa is a smaller version but have some neat pre-designed/jetted complete carb setups for the Honda two-cylinder bikes of the 1970s and early '80s, plus general goodies: http://www.lossaengineering.com Mike's and 650Central started as Yamaha XS650 shops but are branching out into other Yamahas and cafes in general. If you're doing a carb swap I recommend 650Central's VM34-based kit while Mike's has a better “general cafe parts selection” beyond Yamahas including some awesome deals on aluminum hoop rims if they match your spoke counts: http://www.650central.com http://www.mikesxs.net User MurrayF on the CX500 forums is THE top guy anywhere on the CX500/650 and GL500/650 motors and bikes. He's the smallest “shop” I'm mentioning – a cool curmudgeon in a garage who does on-site tuneups in North Carolina and sells carb kits, engine adapters (650 in a 500 frame) and more: http://cx500forum.com The other tiny shop I'm mentioning has the bits needed to turn Honda Comstar rims into spoke hubs – you just have to ignore the words “Do Not Dissassemble” Honda stamped into these rims(!): http://motosynthesis.blogspot.com For custom rims with unlimited hole pattern possibilities and matching spokes, Buchannon's are the people to see: http://www.buchananspokes.net Sudco is a huge general motorcycle parts outlet well known for complete carb kits and can offer custom-jetted solutions for most bikes. They have pre-jetted complete kits for the XS650 and others – look in the “vintage bikes” portion of their catalog: http://www.sudco.com AllBallsRacing are the top people in the world for adapting forks off of one bike to another. To use this page put in your frame's data and it will tell you which donor forks (entire front end with triple trees and such) can be adapted to your bike with the adapter bearings they sell, listed by part number. You need the donor's bike main bolt and nut that goes through the steering head: http://www.allballsracing.com/index.php/forkconversion Summit Racing has the complete line of Supertrapp muffler ends down to 2” inlet sizes that can be used on bikes: http://www.summitracing.com The top cafe modder's general forum seems to be: http://www.dotheton.com/forum You should look up whatever forum is specific to the type of bike you buy! There's also the Reddit http://reddit.com/r/caferacers and http://reddit.com/r/motorcycles forums where I post as user “JimMarch”.

HOW TO PILOT A CAFE RACER A lot of this is my opinion. Grains of salt possibly needed, OK? Go back and watch “On Any Sunday”. There's a whole section on European “GP” sportbike racing of the early 1970s...running rim sizes, types and tire sizes very similar to what we're talking about here. What you'll see is these guys maintaining a full tuck and maximum possible cornering speed, while NOT ever breaking traction at the rear. What they're showing you is what the race guys were doing before a gloriously insane American name of Kenny Roberts came along. Kenny was a dirt-track racer for Team Yamaha, chasing (and often beating) Harleys on the lowly little XS650 modded balls-to-the-wall. Yamaha built a top street race bike (the TZ750 two-stroke triple) and asked Kenny to pilot the thing against the Euro-dominated GP circuit. Who were still riding around with the tires locked down like they were on rails, the poor bastards. Kenny came along and said “well screw that” and started sliding the rear end out. On concrete. We soon learned the translations in French, Italian, German and whaever else for the phrase “what the fuck?”. What Kenny figured out is that by the late 1970s these big two-strokes had so much power that instead of maintaining high cornering speed, you could wrestle 'em round the turn in ugly fashion, point them downrange as quickly as possible (via sliding the rear end) and then “pull the trigger”, blasting out of the corner. Kenny traded high cornering speed for high corner EXIT speed and kicked everybody's asses for years. I now think the reason the “fat rear tire era” started in the race and then street worlds soon after Kenny came along had a lot to do with that rear-slide technique. BUT, and here's where some people are going to scream and yell at me, I have to ask whether or not sliding the rear end around (deliberately) on the street is a good idea? Ummm...yeah, no...it isn't. Now, when I was young and dumb 25 years ago just starting out, I might have said “hell yeah”. But I'm 47 and haven't owned a car in over 25 years and I'm still here...and I'm saying no. I'm still for having some back-road fun now and again, don't get me wrong. But I think the gameplan ought to center around going back to the pre-Kenny days and keeping the dang tires planted. And if you're going to do that, going back to the pre-Kenny-era tires (actually the same basic stuff Kenny himself started on) makes sense. See, the fat tires are NOT needed for traction. I only recently learned this myself...there's a funny counter-intuitive thing going on with traction. If you take a brick and measure how much force it takes to drag it across a parking lot, you'll get exactly the same measurement whether you lay it broad-side-down or on-end. Really. It's the weight and the materials that matter. So a good narrow tire (emphasis on good – Avon seems to have the best cafe-size rubber, Dime City has the full line) can hang right in there with the modern fat-rear-tire boys. And that, folks, can make chasing squids on ratbikes a seriously comical hobby.

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