I don't know how many times I've heard guys say they are afraid to disassemble a carb. "I'll just take it to someone." $400 later, their vintage bike "runs great!" But what happens if it starts acting up again?
I dare say, knowing the basics of a carb is a right of passage for vintage bike owners. Some might say one has no business buying an old bike if they can't sort the carb - at least to stock configuration.
I won't go that far but guys, these are so simple, it's amazing they work so precisely! Sure, the new stuff intimidates - no, wait, irritates me, but these old Mikunis(typical on Yamahas) and Keihins(Hondas) area a cinch so insult yourselves no longer. If you ever built a model as a kid, cooked a complex recipe without an ER visit, or showered yourself without assistance you can do this. Most parts fit together only one way and usually you have another carb to reference. Mikuni's manual is available free online at Sudco's site and elsewhere. It's great info but I did a bunch before finding and reading it. Honestly, once you've done it, you will likely never need to read instructions again.
Here are the tools needed to completely "rebuild" a VM (round slide) Mikuni:
Playa please! A Phillips and small standard screwdrivers, a 6mm socket or wrench(main jet), and a 10mm for the float needle seat. That's it! Few specialty tools exist for most older carbs. Of course syncing them should follow but that's fun to do using a couple of WD40 straws or mercury sticks for you diaphragm guys(insert joke here). There's no doubt you will feel like your bike runs better even if all was okay. The simple adjustments alone might make things better.
The new R5 starts easily but won't stay running on a ride. Actually, the problem is mostly when braking and I remember something weird when using the signals(something foreign to me!) so it's likely a ground but I'm on a carb rant right now so..... Fortunately I enjoy working on these as much as riding them. Today Linda said, "I can't see you buying a turnkey bike." Touche'!
The battery reads 12.4V and 14.3V at 3000rpm (a quick and dirty battery and charging test). There was a loose wire at the battery but that didn't fix it. There's more to check on the R5 - plugs, coils, points, grounds, etc. but the carbs simply have to come apart on any old bike you pick up.
Side rant: Well, if I buy an older bike(pristine tank or not) and it doesn't have inline fuel filters, I can barely sleep until I have cleaned the carbs and put filters in there. It's funny how one symptom can mimic another system problem but that's an old bike for you - and carbs are often it. Cleaning them and reinstalling without filters is plain silly(been there). If you ignore this advice, you will either be best friends with an under-challenged mechanic or become proficient at cleaning your carbs - maybe even good at it on the side of the road in the rain.
Also, second to the, "I'll take it somewhere." is the, "I bought a rebuild kit...."
I'm no pro but with 2-strokes you become good friends with your carbs so I have disassembled, rebuilt, and/or modified carbs a couple dozen times and I have NEVER bought or needed a rebuild "kit". It's like paying for a "tuneup" on a new car with EFI and computer controlled ignition(what do you think they do?!). Anyway, perhaps there is a leak that could benefit from a new gasket but there is little in the kit that will make your old carb work better than cleaning and reusing the old parts. I have bought various jets or emulsion tubes(for mods or tuning) but I can't even remember buying gaskets - well maybe on the Bings(BMW)......... and Amals are gonna leak anyway! CVs are different - I would buy a diaphragm rather than repair one but there are tricks for that too.
This is not a tutorial but just a motivation. Spray carb cleaner is nasty stuff but works great. I just use my parts washer and a brush. If I had a choice between cleaner and compressed air, I'd go with the air. Combine the two and you definitely need safety glasses(I'm typing through misty glasses now). I take a mental note of the position of the adjusting screws - you can always return to that as a baseline although they might have been screwed with to compensate for dirt or poor tuning. I then disassemble, clean, then blow the cleaner out of all the orifices and jets. Takes maybe an hour but I've done it in 15min and I've taken a couple hours while listening to tunes. Don't be tempted to rush or to jam any metal tools into holes - especially the smallest ones(insert another joke here). Remember to be careful as these are pot metal and can mar easily. Don't scar up the carb body with pliers etc. If such coercion is needed, use a towel to protect the metal. Chasing a small orifice with a wire is a no-no as is drilling out a jet. I have coaxed crud out with the nylon bristles of a parts brush and have chased jets with individual bristles in the washer but that's it. If it won't come off with cleaner and a cleaning brush, it's unlikely to come off in use.
Finally, don't leave home without these.
I need to buy a bunch - I think I've picked them up at any dealer counter for about $1 apiece.
Don't be afraid of these things. If you have a problem there's lots of help online and that is what the KC cafe racers group is for........ at least give it a shot!
UPDATE: Rode on the R5 today to the dreaded Kansas inspection station manned by the cargo-pants wearing HiPo. No issues there but the bike started easier and ran much better too. Plenty of power and didn't die once. See! Still need to tune the ignition, etc. but what I thought was electrical wasn't at all. The fuel delivery was just too marginal - fuel fouling a plug or something. Dig in!
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