308 carb strange exhaust sound

Dear members,

has anybody ever heard those sounds?

They appear during descent, throttle up, ending often with backfire.
Top engine has just been renewed, advance, cam clearance and carb setting are supposed to be correctly tuned. At a first glance, exhaust doesn't seem to present any leak.

Thanks for your suggestions.

 

Spitting due to lean fuel mixture?

 

Its very hard to hear what you are talking about. Are you sure the sound is coming from the exhaust and not the intake?

 

I’m rather positive about the exhaust. Noise is much more important on driver side (single exhaust side) than on passenger side (intake).

lean fuel mixture could be the issue. I noticed that with the choke on, almost no more noise, and no more backfiring.

I’ll keep you advised.
Thanks
Dan

 

@ Daniel France: without air filter and just warming up the engine ( be careful, backfire danger! ) you may see the actual "spitting" from the single air trumpets

 

I tend to agree with Morcal. A lean mixture usually shows itself as pops through the intake trumpets.

 

the thing is that it’s impossible to replay the trouble if the engine is not at high rpm with throttle up, like during a steep descent