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Ok so I almost have my motorcycle ready to ride but I can’t get it running right. I have completely disassembled the carb, cleaned every little orifice (after taking it on and off about 10 times), got new jets all around and adjusted the floats.

Here’s where the problem comes, I can unscrew the pilot jet a half turn and it will run, but it runs rich. However if I screw them all the way in it's like it isn't getting gas. Also if I leave them out a half turn they eventually vibrate out more.


The bike is a 1980 Yamaha xs400 with bs carbs. Any help would be appreciated.

Well after 3 weeks of playing with this thing I finally got it. I guess I learned quite a bit on this bike so far. I bought the bike from someone who left it sitting for 3 yrs with gas in the tank and carbs so needless to say the carbs were a complete pain in the butt. But after all of that here is a few pointers if you ever have to go thru this:

1. Clean the carbs good the first time, sounds simple right well not if you don't know what your doing so here is a link to give you an idea of where all the little holes are and how the carb works http://i19.tinypic.com/3324bci.gif it's a good reference, and dont forget the small holes in the float bowl, and you might have to drill out the brass plugs on the BS carbs to get in there to clean just make sure you count the turns and put it back to the same setting you found it mine was 21 half turns from the top.

1.5 make sure after you get it running the first time that you sync the carbs!!!!!! If you dont you will never get them adjusted right. Check here for a good idea for a carb sync tool that costs about $1.55
http://www.powerchutes.com/manometer.asp

2. Replace ALL of the jets!!! they are about 6 bucks a pair and it is well worth it. Check here http://www.mikesxs.net that is where I found them the cheapest. Cleaning them is a pain and you risk making the holes bigger which will only lead to more problems.

3. The book is not always right!! I must have adjusted the floats a hundred times on this thing. The book says 31mm +/- 1mm from the base not even close, I guess with ageing parts you have to find out were they work the best and some times it wont be the factory setting. Mine ended up running best at about 25mm.

4. Have extra spark plugs. After fouling out the first two sets and them contributing to the problem it is good to have a new set for when you get close to the right settings.

Hope this helps someone!!

Dragnfire,

An excellent post. Thanks for writing it up concisely. Well done! How does the bike go on the road now?