Backfire??

[Festy46]

A bent, burned, or sticking intake valve would give you bad compression and allow the energy from the compression and spark plug firing to come up through the carb. Use a compression gauge to check if this might be your problem.

[Johnman45]

I did a leak down test and it wasn't losing any pressure. so i dont know how that can be causing low compression?

[SoCalZ28]

Solid stream of fuel in the carb, timing is on, no vacuum leaks, compression holds... it has to be something... Hmmmm, I still suspect a vacuum leak (consider a crossed vacuum hose wouldn't show a leak) or timing is somehow off. but how bout a shot in the dark. How about the vacuum advance?

[Johnman45]

I have the vac advance and retard hooked up right, how would you check the vacuum advance?

[drddan]

There is a difference between a "misfire" and a "backfire". A vacuum leak should cause a "misfire" and/or rough idle. If you have good compression, as you say, then there is not a bent/burnt valve. If it is a "backfire" the only thing left is timing. A valve is open when it shouldn't be, and causing the gases to be ignited outside of the compression chamber.

Revisit the timing.....

[zoe60]

Maybe the belt is off by a notch or two? Sounds exactly like that hugginsville guy a while back. I don't know if he ever got it fixed. He quit posting. Sure had everybody going though, including myself! watch this if the link works http://www.youtube.com/watch?v=M92CGjpiMs4 Check all of your ignition parts closely. Cracked distributor cap, bad coil? Firing wrong cylinder at the wrong time? How did it run before the carb swap?

[SoCalZ28]

zoe60 makes a good point. How many miles are on the current timing belt?

[Johnman45]

I don't know it has the same one that it had on it that was on it when i got it about 25k miles ago, but the belt looks to be in good condition.

[Festy46]

Try pulling the PCV valve out of the valve cover and hold your thumb over the end of the PCV valve while you "blip" the throttle linkage with the engine running. If that stops the backfire, you need a new PCV valve. I doubt if this is what it is, but we are running out of options. In your original post, you said you had a Weber. Is it a "true" Weber or an Escort carb? Does the mixture screw on the back of the carb have a tamper seal over it? If it has a tamper seal, remove it and back the screw out about 1 turn. I didn't have a backfire condition with my carbs, but by opening that screw a little more, I got better throttle response.

Like a previous poster said, also check the high voltage side of your ignition. Check the distributor for cracks and run the car in total darkness and look for spark jumping between plug wires. A wet ignition system will sometimes give a backfire type condition.