Popping when I get out of throttle.

[GTSpecial39]

I am getting a popping when I get out of the gas. The car seems to be running great, but when cruising at 65 or whatever, when I need to slow down, I get some popping in the exhaust. It isn't too bad, but just bugs me. I have a 71 Mach 1. The engine has been rebuilt, bored .30 over, everything else is new in the motor. I have headers on it and also put an aluminum Edelbrock intake on it and a Holley Quick Fuel 735 carb on it. I did put a mild cam in it, about one step up from a stock cam. I was having a fuel issue with not getting enough fuel and put an electric fuel pump on it with a regulator and am running at 6lbs fuel pressure that cured that issue. But again, if I jump on it or as I said, just cruising down the highway and get out of the gas, its popping. Not sure where to go to figure out why and to cure it. Any thoughts would be appreciated. Thanks!!

 

[Hemikiller]

Popping in the exhaust can be caused by a leak, which allows air to enter, or an overly rich mixture. A simple test for an exhaust leak is to have a helper plug the tailpipes with rags or towels. The leak will be apparent as a hissing sound as pressure builds in the system.

 

[GTSpecial39]

Will give that a try! I also have electric dumps on it. Seems it does it a little more with the dumps open.I also was wondering, with what you said about an overly rich mixture if I back the fuel pressure to like 5 or 5.5 might help it. Had someone else mention maybe the timing is too far advance. If I remember right, my friend set it at 14 degrees.

 

[Steve McMahan]

Some people prefer using a smoke machine to find an exhaust leak. That worked for me, no more popping.

 

[GTSpecial39]

Some people prefer using a smoke machine to find an exhaust leak. That worked for me, no more popping.

Thanks for the info, I will figure it out one way or another!!!

 

[basstrix]

On just about every 4-stroke motorcycle I've owned, the telltale sign, that it was time to switch the gas valve to reserve and fill up the gas tank, was the popping from exhaust on decel. I always assumed it was the carb going lean due to a low float level...but I honestly don't know the true mechanism. In general, none of them had exhaust leaks. I'm not arguing what Hemi said, because I've seen that scenario as well. I'd start by looking for exhaust leaks and none are found, maybe check float level??

 

[GTSpecial39]

On just about every 4-stroke motorcycle I've owned, the telltale sign, that it was time to switch the gas valve to reserve and fill up the gas tank, was the popping from exhaust on decel. I always assumed it was the carb going lean due to a low float level...but I honestly don't know the true mechanism. In general, none of them had exhaust leaks. I'm not arguing what Hemi said, because I've seen that scenario as well. I'd start by looking for exhaust leaks and none are found, maybe check float level??

Thanks for you input, greatly appreciated!!

 

[GTSpecial39]

Thanks for the info!!!!

 

[cjstaci]

You wrote it does it on deceleration then added does it when you jump on it. Also cam is one step above stock and timing at 14 degrees.
I don’t what the duration spec’s are, but assuming the cam is very mild you may have too much timing. At 14degrees initial, what is the total timing? Do you have vacuum advance? If so, should be hooked up to ported vacuum source. Try backing your initial advance to 10 degrees and see if that helps.