Backfire at high revs

[mattsay]

Hi John,
I'll be sure to let you know. If it works I'll be delighted and even more so if it helps others too.
Cheers,
Matt.

[KOY 23]

What was changed or altered immediately before you had the backfiring?

[mattsay]

That's what's puzzling me. I normally mess about with things and realise that I shouln't unless I know what I'm doing. On this occasion I can't think of anything.

[Ian Durrant]

I just thought of one other outside possibility(i.e check this last). check the valve clearances. If you have an exhaust valve spring thats broken for example, then you may get unburnt fuel being pushed into the exhaust that then ignites when the exhaust temp is hotter at high revs.

Bearing in mind you have a good degree of confidence it the other things I mentioned I think that others are probably right that its going lean at high revs.

What I keep having to relearn myself though is not to overlook things because they are fairly new or thought to be good.

Kind regards
Ian

[mattsay]

Ian,
I agree that all that is new is not good. I have an ostrich (head in the sand) fear that my problem is valve related. I would have thought that if it was a common prob (backfiring that is), there would be many people saying "that's just what I had and it only cost 10p to fix" - somehow I don't seem to experience that very often.
Jets to the rescue!
BR,
Matt.