Motorcycle Repair: carb problem, air fuel mixture, mixture settings

Question
hi chris, i need help. i am a lic car mechanic. i have a 1982 honda cb750 DOHC custom. my engine lost compression on all cylinders. so i replace the engine with a good running engine, but the engine i put in the bike came out of a 1980 honda cb900 DOHC custom. i got the engine in the bike but it will not stay running. i installed individual air filters on each carb. the carb are of the 750. i think i have to rejet the carbs so they are the same as a 900. my question is do you know the jet size i will have to install to make the 750 carbs work on a 900? and do i have to adjust the air/fuel mixture do to the air box is not on the bike?

Answer
Hi Steven.
 As you well know, adjusting mixture settings is a tricky business.  You will be better off just getting the correct carbs for that engine, if they are available.
 If they are not available (new or used), then rejetting the carbs is the only option left.  As far as what needle size you need, I do not know.  What you could do is try to find the FACTORY repair manual for the bike (check www.repairmanuals.com for that).  It is usually a little more expensive than the Clymers, but it has the needle sizes and settings as well as all of the correct specs on the bike and engine.

 If the factory manual is not available, then check with a good independant shop or the local Honda dealer and see what needles you need and make sure that they will go into the 750 carbs.
 You may find that you only need to reset the existing needles for the new engine, but make sure that that they are completely compatible, if you must replace them.

 Just make sure that when you set them that all four carbs are set exactly the same, or you will be fouling out or burning up some of the plugs on the bike.

Good luck.
FALCON