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?

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.

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

micklewright wrote: 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.