Engine Backfire

[Terry B.]

Help!, I have a 1970 350/350 that has suddenly developed a severe rough running and backfiring problem. The backfiring is so great that it has blown out both mufflers. I don't think this is a carb problem as I have switched carbs and have the same problem. The car has finally quite running. Could this be a coil problem. I have pulled one of the plugs and it is soaked with gas...Any thoughts?

[Terry B.]

Re: Engine Backfire

Terry,

I heard it yesterday from my house. I thought you had a new addition to your stable and just getting it adjusted. It was really running rough. I'm sure you did not do anything different with this winter's storage that you have not done in past winters with the gas? I had a similar problem about a year and a half ago that turned out to be with the distributor and timing. Roger Owsley solved that problem for me.

Maybe after you get it all fixed, the off road mufflers will sound perfect. I hope you do not have to replace them.

[Tom H.]

Re: Engine Backfire

I would agree that you might have a timing issue. Have you done any recent work or changed anything at all on the engine that may help aid in the diagnosis ??

Didn't change plug wires or anything did you ??? ( Possibly have wires crossed ?? )

You also might look to see if a rocker arm has come loose.

Could be anything at this point, so we'll have to start eliminating the basics. Report back in with what you can eliminate. We'll get it going !!

[Terry B.]

Re: Engine Backfire

Tom, Thx for the response. Didn't do any recent work, just fired it up from and a couple of miles from my house, it started missing and backfiring...will continue to check ignition system

[Tom H.]

Re: Engine Backfire

Terry:

Do the simple stuff first. How old is the fuel? Pop the cap and take a whiff. Make sure it didn't go bad on ya !

[Terry B.]

Re: Engine Backfire

Terry,

Thx for the response. Both mufflers are physically blown apart at the seems so I will have to get new mufflers once I get the problem fixed...

Terry

[Michael W.]

Re: Engine Backfire

Most cases of after fire (not backfire) like this are the result of unburnt fuel making it's way into the exhaust system and then being ignited. Faulty ignition is almost always the root cause. have a look at the points, condenser or electronic equivalents if applicable.

[Joseph K.]

Re: Engine Backfire

Terry,

I agree with the other ideas. To get allot of fuel in the exhaust to ignite is not a good thing. To run OK and then suddenly run very ruff.... could the timing chain jumped a tooth. Has the engine ever been rebuilt? As mentioned above this will be a process of elimination.

[Terry B.]

Re: Engine Backfire

Joe/Mike,

Thanks for your replies. Sounds like you both agree my problem is with the timing/ignition system and not the fuel system. Engine was rebuilt about 40K miles ago. I'll start with points, etc and hope it's not the timing chain...

[Robert G.]

Re: Engine Backfire

I would try the condensor. I had a similar problem where the car ran fine until it warmed up and then it started afterfiring and running poorly. It was a bad condensor.

[Rob M.]

Re: Engine Backfire

I had once the same problem, new condensor and the car runned smooth again...

regards,
Rob.

[Terry B.]

Re: Engine Backfire

I'll try that...Thx

[Tom L.]

Re: Engine Backfire

Ditto on Robert and Rob. Also check that the Vacuum advance can is functioning properly.

[Terry B.]

Re: Engine Backfire

Will do..Thx Lynn

[Duke W.]

Re: Engine Backfire

Could be burned points or a shorted condenser. You need to systematically check everything in the ignition system including the coil, cap, rotor, breaker plate ground, secondary wire resistance which should be no more than about 5K ohms/foot.

Exercise the breaker plate with a vacuum pump on the VAC while checking that you have continuity between the breaker plate and ground. The ground wire soldered to the breaker plate is continually flexed while the VAC is moving, and will eventually go open - often intermittently, which will cause the symptoms you report.

Duke