Why does the exhaust Backfire when there is a lean mixture?
I can understand a rich mixture causing incomplete combustion.
Thanks
Chris

 

A lean condition in an engine can cause exhaust backfires when the air-fuel mixture doesn't have enough fuel and too much air. When this mixture combusts, it burns more slowly, so there's still unburned fuel in the exhaust when the valves open. This fuel can then explode and create a loud popping sound.

 

Thank you!
Seems counter intuitive but you did a great job explaining it.
Chris

 

Intake leak can cause that, as well as the carb cough.

Please don't say you've checked by spraying fluid everywhere, that only works when there is a massive leak in which case it'd be difficult to even start.

 

I've come to the conclusion just to replace the gaskets as maintenance item. I have the blue "James" gaskets on the bench.

 

I never had much luck with those blue James gaskets. Hopefully your results will vary.

 

Pair of Cometics, just in case 😁

 

I've never had blue James not seal, but have warped the flanges every time I used them. They seal with blue James but if you ever want to use any other (stock type) brand, you'll need to buy new flanges.

And, maybe not S&S (they are $85, OEM are half that) any off brand flange is subject to be warped out of the box just enough... you know the rest.

 

Thanks!
Having spare parts is better than waiting for parts.

 

Absolutely !