Backfire! Help! So frustrated!

[pjdeb]

Originally Posted by Bill G

Backfires can be from running lean. You might also check for good gasket seal around the manifolds and check for cracked manifolds and make sure that the vacuum port for a vacuum wiper is not opened up.

Thank you for the replies.

Update: compression 60, 62,62,64.
I do not think it is manifold or vacuum leak as it runs well at idle.

I checked two zenith carbs for float level. Both seem to be about 3/4 to the seam using the gage tube from the drain plug. I mean need shims. I will order, but I do not think that is the real problem.

Ran some seafoam into carb at high revs. Run for a couple of minutes.

Put some MMO into cylinders. Turn it over with the crank. Put some more in to sit overnight. In the morning I will smoke out the neighborhood.

After that I will try yet another set of plugs. Running Autolite 3076. Probably not the best, but I have run them for a few years. They run black. GAV is completely closed.

I hear what you are saying about "new" parts. I do not have a way to test them, unfortunately. I am getting good spark from the coil when holding the wire end close to a stud.

I do appreciate your help.