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This is happens while slowing down with engine. Like going down hill and letting the engine slow you down. Is this caused by the timing being off? I never noticed it until I adjusted the timing. Thought I got it right but it was very hard to see on the early style engine. Is there a trick to seeing staight on to see the timing mark on the early style engines?
Thanks, Gerry 51 M38

Gerry,
Retarded timing will cause the backfire. Too rich a mixture will cause the backfire. The two combined, IE your mixture was too rich but your timing was advanced a little far then you retard the timing where it's suppose to and suddenly you now notice the carb is running too rich.

Wes, I will double check the timing. There is no way of adjusting the carb is there ? It was rebuilt last spring by a very reputable person. Wes is there any trick at looking in to see the timing marks better on the early style engine, Thanks,

Just clean the area real well and mark the firing mark (5 deg) with a dayglow orange or green paint. Then draw a bisecting line across the window and paint it dayglow orange or green.

It depends on what he used for a kit or parts. On the metering rod side a wrong spring, wrong rod or bad (NOS 40 years old) diaphram can disrupt or corrupt the mixture system.

A small exhaust leak can also cause popping on decel.

Wes I marked it but I find it hard to get a staight on view. I did it from underneath with someone else turning the distributor. I thought if I did it from above the angle would make my timing marks be off.
Petesilfven, Thanks for the input but I have a new exaust system and it appears to not have any leaks.

Hi,

I use a 6"x6" mirror to view the early timing hole. It takes a little practice to get the light and the mirror in the correct place but when you do there is a good view.

Bob W

Bob, Thanks I was thinking on trying that. Now I know it will work.