carb ID and Which to use

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Bigzakdaddy

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hello all-

new member looking for some direction. I bought a bike with two sets of carbs. please help me identify the different carbs by telling me the names of each kind. obviously their both mikuni, but is there a model number they are? The smaller of the carb sets (on left) was mounted on the bike and does run with them, just poorly and pours fuel on the ground. the larger of the carbs looks the same but doesnt line up to the manifolds. is there an adapter? is it even worth the energy? or is the one pouring fuel on the ground worth fixing? i have many more pictures if nessessary. thanks in advance for your time!!

Zak
 

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now that jayel has helped me identify the differences, which was an excellent reference, thanks!!, bs34cv(small) bs38cv(large), which of the two is the better performer? are there manifolds made to fit my engine?
 
Bigzakdaddy said:
now that jayel has helped me identify the differences, which was an excellent reference, thanks!!, bs34cv(small) bs38cv(large), which of the two is the better performer? are there manifolds made to fit my engine?
Click to expand...

yes intakes for both are availible then comes the air cleaner/air filter ? depends what you want to use and/or do with the bike, 34's probably a little better mpg (EPA)carbs, 38's maybe a little better for preformance not noticibly tho' pics of the bike would help and a idea of what you intend to do with it:bike:
 
bill, i had an interesting time getting this bike to life as the p/o put 2 bikes together, both in different time lines. i bought the pamco ultimate ignition and corrected the not running at all thing. the engine had bs34's on it and as previously mentioned, not running very well. after reading more, i can only assume my engine is 80-83, (because the bs34 carbs and manifolds all fit perfectly). no major mods, just looking for a reliable barhopper!! 38's or 34's? and are there different carb holders? heres the bike...
 

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You can check engine year by looking on the front of it for the serial number.
I have 34's on my '81, which is stock of course, and love 'em. Of course it took 3 months to get them purring. I can't stress the importance of that carb guide. Over-looking the guide or trying to just throw them together will not work. You can get them going, but it will run, and sound, like complete shit. Other parts such as cam chain adjuster, valve lash, timing, need to be adjusted before the carbs. Grizld1 will be the first to tell you this. He is co-author of the carb guide. There is absolutely no set recipe for any bike or set of components. Time, testing, and patience. Someone might have the exact same set-up as you, but needs a different set of jets to run right.
 
Your 38s appear to be a '78-'79 set, the last made and the best of the 38s in my opinion. If your 34 float bowls have a brass nut for a drain plug like the 38s, they're a 1980 set. If they have a screw in the lower side for a drain, they're an '81 or newer set. If they're an '80 set, they will have brass floats. If the floats need replacing, the only place to get them is from a Yamaha dealer @ like $30-$35 each. If they are bad, it would probably be cheaper to rebuild and use the 38s.

The inlet stubs on the 2 carb sets have different O.D.s so different manifolds are needed for each set. Either will mount to any 650 engine. 34 airbox may not mate up to 38 carbs and vice versa. Most of us just use separate pod filters in that case.
 
excellent information from all. well done!! an hour ago, i knew very little on this subject. looks like i should order a few parts, get the 38's rebuilt, have it proffessionally synced and gone over by yamaha, and ill be rocking down the highway. well, in theory....right?


Thanks to all again!!
 
If you have any hope of making this an economical ride, you'll need to learn how to do most of that stuff on your own. A carb "rebuild" consists mostly of a thorough disassembly and cleaning. Usually not too many replacement parts are needed. Carb syncing is pretty easy with the use of a homemade manometer (less than $10 to build). All the other tune-up stuff (valves, timing, cam chain) isn't hard once you do it a few times.
 
5twins- I know I need to do more, and I plan to. My primary goal is for it to be reliable. I don't want to make rookie mistakes that will leave me on the side of the road. Call me crazy, but, I plan to spend slot of time on this thing. I just want it to be right!!
 
Bigzakdaddy;

5twins has given you some good advice there. These bikes are very easy to work on and tune up. Yamaha dealers don't want to work on bikes that are this old.............their mechanics work on fuel injected/computer controlled engines. Have you ever checked their hourly shop rate?

Take some time to read up on these bikes..............there is an amazing amount of information available. Start with the "Tech" section on this site. Also use the search function. Become your own mechanic............save money and you'll enjoy the bike more.
 
Plus, you can be the cool guy next door. :thumbsup:
My neighbor has a beautiful Harley. Ask him how to change the oil and he is lost. I was adjusting my valves, and such, when I looked over to see him and 2 of his friends loading his bike on a truck. Well, a bunch of money, and time, later, I found out from his son that he had a bad spark plug. His son said it cost over $300.00!!!!! for a $5.00 plug. But he's got the cromiest-crome bike in the 'hood.
Knowing your bike will not only save you money, but helps you fix things, like if you were stuck on the side of the road or to help others diagnose problems.
 
I'm gonna have to agree with everyone else. These carbs are simple to work on and the sastisfaction of knowing you have it right and done it yourself is unparalleled by any shop work. Not to mention any time you decide to modify something in the motor you may have to change your carb settings again. Take the money you saved and buy a donut to sit on after that hardtail beats your mud ring out:yikes:
 
Great info from all the guys here for sure. I find these carbs very easy to work on. Cleaning completely can be time consuming, but not hard. There is a guy in the forum here that will clean, rebuild and get you some baseline jetting. He is in the shops section http://www.xs650.com/forum/showthread.php?t=5817 might give him a shout. Appears his base price is $50, try getting that at a Yammie dealer :yikes: :thumbsup:


Bigzakdaddy said:
5twins- I know I need to do more, and I plan to. My primary goal is for it to be reliable. I don't want to make rookie mistakes that will leave me on the side of the road. Call me crazy, but, I plan to spend slot of time on this thing. I just want it to be right!!
Click to expand...
 
I didn't know shit about working on bikes till I bought my XS, carbs, wiring, and valves were a mystery to me.
After several years of ownership, I know a little more shit than I used to but still have a lot to learn, but at least I can work on my own bike on the side of the road. I recommend you try doing it yourself too.

Beauty of this forum is you can ask a ? that's been asked 100 times before and no one will give you a hard time, just an answer.
 

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