Engine misfires

[maranci]

Dear All
Hope you can help me out with this one. Since the day I bought my bike, sometimes the engines misfires on starting and usually it continues working on three cylinders only since the 4th spark plug would not work, which I suspect having a greater amount of petrol than needed. Whenever I start the bike with some choke, this happens most frequently. This also happens on the three other plugs, so there is no configuration, sometimes is No. 1 cyl, sometimes it's No. 4, sometimes it's No.3 and so on. Lately I have sent my bike to a mechanic where he cleaned and set the carburettors with vacuum gauges. Is it possible that I am not putting the correct type of spark plug? or else my bike needs a hotter plug. I always fitted NGK CR8EH9 plugs which are the recommended. Could anyone tell what is happening or how can I fix the problem?

[Cammo]

It sounds as though your carb pilot scres need adjusting, these are what control the mixture during idle. If they're set too rich it can cause issues like you describe.

I would think that the mechanic would have checked the pilot screws while he balanced the carbs, but might be worth asking him if they were done.

[micklewright]

on pilot adjustment.

Sounds like pretty standard plug fouling from rich mixture, especially with it running on 3 on occassion. On older bikes I'd be checking for possible oil fouling.

New plugs on the first few fires/rides may give a better indication of the/a problem

[maranci]

on pilot adjustment.

Sounds like pretty standard plug fouling from rich mixture, especially with it running on 3 on occassion. On older bikes I'd be checking for possible oil fouling.

New plugs on the first few fires/rides may give a better indication of the/a problem

Thanks for your reply. When one of the plugs seems not to be working for two or three times consecutively, I change only that plug and the bike works well. So it seems that maybe the plugs need more changing. I usually change my plugs after about 7000 kms. I don't know exactly when these plugs need changing. Also when I remove them to clean them, there would be no sign of oil deposits on them.