Recently aquired a 69 Dart, 6cyl 4 speed, At first the car ran great but then last weekend the car flooded real bad which resulted in me having to pull the plugs, cleaning out the cylinders and replacing with new plugs.
After giving it a test drive it did OK until the motor heated up then I had a bad backfire when giving it some gas in 1st or 2nd. Since then I have changed the plugs again, replaced distributor (installed vacuum advance)
set timing to 6@ with vacuum advance plugged off then reinstalled. Today again I tried to get her out and once agin it started backfiring under load after about 10 min's of driving. (It seems to get worse as the car gets hotter). The car's a 69 but the motor is a 79 or 80 my guess. I'm new to car restoration so any help would be appreciated.

I also checked the volts at the coil getting 7.6. Is that to low or OK.

Thanks
5258

Electronic or points ignition?
If it still has points change the condensor and the distributor cap.
DD

Electronic ignition.

OK here's the latest info about the 69, I adjusted the valves which has the car idling alot smoother, the back firing problem still exsists, I have found as the car heats up so does the coil, as the coil heats up (25-30 min of driving) the volts goes from about 10.7 to 8.0 range and then when under load the car backfires. I have traced all wiring back and everything looks correct. What should I look at next?

I also removed the ballast transistor which jumped the volts at the coil up a little which helped but did not fix.

5258

It sounds like either consciously or subconsciously you believe it is the ignition coil. They're cheap enough, give it a try. Some other things that could be causing your problem is a burnt valve or bad timing chain. To check for burnt valve, do a compression test both dry and wet. If you have low compression numbers in a cylinder or two, squirt some oil in the cylinder and see if the numbers shoot up. If they are still low, I'd suspect a burnt valve. To check the timing chain, pull the distributor cap and (with all the plugs out) rotate the engine around to TDC in the normal rotation direction. While watching the distributor rotor, turn the engine back wards SLOWLY and stop as soon as you see the rotor start turning. Look at your timing marks. This is how many degrees of slop you have. If more than about 8*, the chain/gears are suspect. The late 70s engines used the "silent chain" set-up with the nylon surround on the cam gear and the nylon will break off giving you way too much slop.

Mike
www.PowreHaus.com

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Have you checked your plug wires? You didn't mention them. Arching between wires can be most prevalent under load. If they were old and brittle, they may have been damaged when you pulled the plugs. Even if they were newer, they can be damaged easily. I'd check them, or replace them, just to be sure.

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DynoDave
1970 Plymouth Duster
1972 Dodge Charger Rallye
1977 Chrysler Cordoba
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