Yeah all valves re lapped. Like I say noticed that the compressor i used whilst doing the heads on my other engine bent one so just thinking if it did that removing could have done it replacing. What is confusing is its not regulary it can vary between 5-10secs so if it was the exhaust it would do it on every cycle would it not?

scotjell wrote:Yeah all valves re lapped. Like I say noticed that the compressor i used whilst doing the heads on my other engine bent one so just thinking if it did that removing could have done it replacing. What is confusing is its not regulary it can vary between 5-10secs so if it was the exhaust it would do it on every cycle would it not?

Not really.

These things vary, if you have a leak it may take time for air / fuel to build up in the pipes.

Are your carbs balanced I can't recally?

If so check the exhaust system for leaks.. it sounds lean to me.

The only other thing I can think of is Knackered plugs / bad ignition system letting unburned fuel into the exhuasts every so often which is igniting. This could be down to plugs, CDI, leaking HT leads.

Have you tried new plugs in it?