Snapping and popping

I recently removed the stock style muffler on my modified Model A Ford banger and ran a straight pipe all the way to the rear of the car, just for fun and to keep the noise and fumes behind me.

Once warmed up there is a fair amount of snapping and popping from the exhaust on overrun. By overrun I mean moderate to strong engine decceleration when lifting off the throttle when under load. There is no backfire through the carburetor.

It sounds cool, but is also kind of a nuisance. I am curious as to what causes this phenomenon. I am going to put on a Smithy's muffler relatively soon, so not to annoy the neighbors and the Law.

Thanks in advance for any help.

Peace

 

When the motor is turning at a good RPM and you close the throttle, not enough air is there to burn fuel in the combustion chamber so fuel is drawn into the exhaust pipe. The heat there will ignite it. Watch the exhaust area of the cars in a nascar race.

 

Thanks Don!

Now I understand

 

It can also be caused by a lean mixture or air entering the exhaust system, try opening the idle mixture screw another turn and see what it does.

 

^^What he said

 

Cracking and popping instead of flame in exhaust on decel. often comes from air leak into exhaust on decel. that you prolly ain't hearing as a leak on accel. because of sound volume of straight pipe.
Dave