Popping on overrun

[mark030358]

Just a quick question..

When hot my sprint sometimes "pops" on the overrun, what is the cause of this? It does not do it when cold...

.... and whats the fix??

cheers
Mark

[MintSprint]

Usually, it's down to an air leak in the exhaust manifold somewhere (either a crack, or a leak at the Y-piece where the branches of the manifold join). Air is drawn in and unburnt fuel explodes in the exhaust, causing the popping.

Less likely, but possible, is a burnt valve causing the same symptoms.

Check for leaks, and if you can't find anything, do a compression check for the valves.

Ignition timing can also have an influence, so it may be worth getting that checked, too.

[john.p.clegg]

A weak mixture will do it,not igniting in the cylinder but burning in the exhaust...

John

[steveww]

Mine had a bit of popping on the over run, advancing the ignition a tad cured it.

[mark030358]

I think I'll go for the exhaust sucking in air... as from memory there was a small amount of carbon around the Y piece.

many thanks
Mark