Engine pops (slight backfire) M38

[Gerry]

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

[wesk]

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.

[Gerry]

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,

[wesk]

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.

[petesilfven]

A small exhaust leak can also cause popping on decel.

[Gerry]

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.

[BobW]

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

[Gerry]

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