I have a thunderheader on my 1978 lowrider and I'm getting decel popping. Using a super e carb and I believe its tuned correctly. Is this typical of this pipe?

 

Poping comes from exhaust leaks. Improper fuel/air. There are lots of reason.

 

Might be exhaust leak and the plugs look right on.

 

Did this start when you initially put the thunderheader on? and was it recently?

 

It has from when first installed. Its driving me nuts. Tried richer and leaner too. I'm thinking its the exhaust gaskets leaking so I replaced them yesterday and static timed the motor. I still have to replace the front brake switch before I start it up and ride it.

 

Could very well be pipes gaskets at the head. Cheap enough to replace. Also, How old is you carb? Sometimes if a throttle plate shaft gets worn the Throttle plate will not seat properly, so when deceling it can actually suck fuel into the combustion chamber and cause that same popping. Typical old worn carb....

 

Its a newer super e. I might have about 2,500 miles on it.

 

K, rules that out. maybe the gaskets will help. what jets are you running and what exactly do you have in the motor, and what do the plugs look like?

 

74 inch motor, 30 over 9:1 pistons, fresh head job, S&S 450s cam and hydrolic lifters. Ultima single fire ignition without voes (will get one soon). I don't remember the exact jetting but I think I have it written down somewhere. The carb seems to be jetted properly, within the guidelines S&S says the accelerator pump and mixture setting should be at and the plugs look to be burning good with some carbon on the insulator and end of threads. I think I'll check the cranking compression. Any idea what it should be?

 

Depends on what cam your running, how many cc's are the heads. What the deck clearance is etc. It could be anywhere from165-190.