I am having a problem I think with my timing. I just recently began a mild restomod of my '66 Coupe. It has a 289, Edelbrock 4V and intake, Edelbrock RV cam, Heddman Headers and Petronix ignition. The problem I am having is that under hard acceleration I am getting some popping through the exhaust. It starts of as a slight pop and by the time I get up to 60 mph it is a pretty loud back fire. I have adjusted the timing and carb and seen some improvement but it is still there. Thanks in advance.

 

Have you checkedyour wires tomake sure they are not arcing to each other and causing a cross fire. Does it only do it under a load ?

 

All new Moroso wires with looms. I don't see any evidence of arching. Yes, it only does it under load. The more load the more popping. Cruising at 30 mph there is just a slight popping. When I accelerate either hard or easy the popping gets louder and more regular. I am thinking I need to readjust my valves as I also put in new hydraulic lifters with the cam. Does this seem like I'm on the right track? I know one of the lifters starts tapping after engine gets on temp.

 

How's the ignition timing? Extremely retarded timing could cause this. Under low-load, the VA gives enough advance to keep it running ok, but that extra advance goes away under a load.

 

That was part of the problem. I corrected it and got some improvement. It was backfiring right off the line, now it just pops a little and gets worse as the load increases.

 

are you sure you didnt skip a tooth when you put the dizzy back in?

 

Well no not SUREThat is another possibility I have considered.

 

hmm, id almost be temped to start over, and make sure all the wires are going to right plugs as well. also, the dizzy COULD be ceased up... just another thing you may wanna check. that could also make the popping if the dizzy isnt working properly

 

As long as you got the timing you wanted when you did it, you'll be fine. Even two teeth off is ok and long as you have enough room to turn it to get you initial and total timing where you want it.
I'd check to make sure you didn't cross two wires in the firing order. Sometimes you can't even tell except for random pops if it's only two of them.Check the preload on that one lifter. Flat tappets seem to like a little more preload than rollers for some reason.
Check initial and total without the vacuum advance to see if Staryfury is right.

 

I checked the VA today. Well I sucked on the vacuum line and the VA moved and held so the diaphram is ok. I reckon it would be well spent time to go over the wires again. Especially since now that I think about I don't think I had this problem until the last wire change. Unfortunately I don't get to spend time with my car daily so things tend to get kinda foggy.[sm=smiley19.gif]