Motorcycle Repair: yamaha, inexpensive test, valve clearances

Question
hi mark i am still having probs with xj 900f it is starting on 3 cyls if you leave it running after about 1min it sort of surges onto 4 cyls if you rev it it stays on 4 and sounds ok i have cleaned carbs and replaced with diferent set and also replaced coils it is always the same cylinder that misses could it be valve clearence as when it warms up seems to be on all 4 any thoughts thankyou.

Answer
Hi Mick,

I suspect an enrichment circuit passageway remains obstructed and is causing the problem. Here's my reasoning: During engine starting the problem is present (enrichment circuit or "choke"). After engine begins to warm, problem cylinder seems to start firing (coming off enrichment circuit). With throttle, problem cylinder seems normal (completely off enrichment circuit).  

I doubt valve clearance is the cause. However, I encourage you to measure and ensure valve clearances are within service limits for the sake of maintaining the engine.

Did I email you carburetor cleaning information files before? If not, gimmie your email address and I'll send.

Did other ignition coils test defective? Avoid the temptation to replace parts in attempt to fix a problem unless absolutely certain that the part is defective. Tests are simple and can be done with inexpensive test meters (VOM/multimeter). Guessing is expensive and makes our wives unhappy, which fuels our problems. : )

Respectfully,
Mark Shively