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Old 10-10-2018, 09:39 PM   #1
Cape Codder
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Default Terriable backfiring

My car has been running badly for quite some time. The latest problem is it is Backfiring! I have changed the condenser which did not help. I tried to take it out for a ride today and as usual, I took it out of the garage to let it warm up. While it was running it Backfired, at idle and then shut down. Any idea's?
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Old 10-10-2018, 09:45 PM   #2
Chuck Sea/Tac
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Default Re: Terriable backfiring

Does it idle smoothly?
Is it hard to get it to idle?
I would look for a leaky intake gasket or cracked manifold
Try shorting each plug, one at a time and see if that changes the idle. That will narrow down a lean cylinder.
Do you have full flow gas feeding the carb?
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Old 10-10-2018, 10:28 PM   #3
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Default Re: Terriable backfiring

Chuck Sea/Tac Thanks for the response and ideas.
Idle seems to be smooth and not hard to get to idle.
I recently changed the intake/exhaust manifold gasket (can't say when).
I will check for the leaky intake gasket or cracked manifold.
The other two suggestions I will try tomorrow.
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Old 10-10-2018, 10:33 PM   #4
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Default Re: Terriable backfiring

Check your GAV. You might be running it too lean. Leaning it out will cause backfiring. Another issue I saw on another person's car was some dirt or something in the distributor causing cross-fire to wrong cylinders. In that case a new distributor body and cap solved the problem.
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Old 10-10-2018, 10:39 PM   #5
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Default Re: Terriable backfiring

Had you remembered to advance the spark after starting?
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Old 10-10-2018, 11:03 PM   #6
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Default Re: Terriable backfiring

Closing point gap?
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Old 10-10-2018, 11:09 PM   #7
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Default Re: Terriable backfiring

Use a propane torch, unlit. Turn the gas on and direct the gas stream around the intake manifold as the engine is running. If there is a change you have a leak. Can also use WD40 but it makes a bit of a mess.
As previously posted. Check point gap. Usually point gap too close makes for hard starting as well.
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Last edited by eagle; 10-10-2018 at 11:14 PM.
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Old 10-10-2018, 11:58 PM   #8
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Default Re: Terriable backfiring

Have you played with anything lately? If so and it was running OK beforehand, that is the place to start looking.
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Old 10-11-2018, 06:05 AM   #9
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Default Re: Terriable backfiring

Try a condenser that you know is good, not a new one. A bad new one can really fool you.
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Old 10-11-2018, 07:45 AM   #10
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Default Re: Terriable backfiring

Make sure the spring is not broken on the point arm. We had one where it would idle, but at speed, the broken spring would let the arm float. Just feel it to make sure there is guts to spring.
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Old 10-11-2018, 09:00 AM   #11
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Default Re: Terriable backfiring

I had one that would start and idle but when I gave it gas it would backfire. It had been sitting for a little while. Critters crawled into the exhaust and plugged up the muffler.

I removed the muffler and shook all the acorns and nesting out. It stopped backfiring.
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Old 10-11-2018, 09:41 AM   #12
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Default Re: Terriable backfiring

How can I check a new condenser to see it is good?
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Old 10-11-2018, 10:01 AM   #13
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Default Re: Terriable backfiring

Hook both us. They can't both be bad. It won't hurt anything. Just use some jumpers to ground the loose one and to connect it to the passenger side of the coil.
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Old 10-11-2018, 10:10 AM   #14
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Default Re: Terriable backfiring

It is also possible that you have a cracked distributor body or a brake-down in the insulation between the leads in the body. A number of years ago some repo bodies were defective and would crack near where the #4 internal lead went past the #3 plug lead causing the a short between the #3 and #4. This short is very visible if you run at an idle in a dark garage, check along the edges of the body near where the plug leads are close to the body. Try another distributor body. After I found out about this problem we had a tune-up clinic and I found about 1/3 of our clubs cars had bad distributor bodies.
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Old 10-11-2018, 10:58 AM   #15
Ernie Vitucci
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Default Re: Terriable backfiring

Good Morning...A few more odd things to check would be the nuts on the back of your amp meter and the nuts on the back of your ignition switch if you have an after market switch instead of the original pop out. Another spot that can be a problem is the little fuse box on the side of the starter. The rivet can work lose and the connection can be lost and it will behave as if you are turning the ignition off and on. Just remove the little box and put things back like Henry had them for an hour or so and see if the problem goes away. Good Luck...Ernie in Arizona
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Old 10-11-2018, 03:28 PM   #16
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Default Re: Terriable backfiring

That's right. If you have a make-break condition in the circuit from the coil to the point arm, it will backfire.
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Old 10-11-2018, 04:23 PM   #17
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Default Re: Terriable backfiring

Quote:
Originally Posted by Jacksonlll View Post
That's right. If you have a make-break condition in the circuit from the coil to the point arm, it will backfire.
Some repro switches have loose terminals at the back. Give them a wiggle (I love these technical terms!) to check. If there is any movement, get back and I'll expain again how to fix it.
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Old 10-13-2018, 06:55 PM   #18
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Default Re: Terriable backfiring

FIRST I want to thank everyone that has responded to my "Terrible backfiring" post.

We have tried: changing the distributor body & cap, re-gapped the points, changed the condenser, changed the coil & coil wire, re-timed the engine, checked for vacuum leaks at the intake/exhaust manifolds, did I say retimed the engine cause I forgot to tighten the screw on the cam, used a jumper to check the ignition switch, adjusted the GAV from almost closed to 1/4, 1/2, and maybe as much as 3/4. After these few checks, we still have a Terrible Backfiring.

Soooo.......we are thinking of changing the plugs. We found the washers? on the bottom of plugs crushed and don't seem to be sealing. Don't know for sure about that but they sure are flat. However, the plug tips are a lite tan color with no oil or soot.

I have Champion W16Y plugs in there now but which one do most use looking at the below chart which was posted by someone on this site? Should I have a hotter or colder plug?

Champion (hotter down to colder):

W95D
W89D
W16Y
W20
W18
W14
W10
W85N
W80N

Thanks for any help you can supply because we are at witts end with this problem.
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Old 10-13-2018, 07:16 PM   #19
DJ S
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Default Re: Terriable backfiring

I think you need to investigate beyond your ignition system. If your sparkplug washers were "crushed" and causing a bad seal, you would hear air rushing out around the plugs when cranking over the motor.

Have you conducted tests to check on the health of your motor?
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Old 10-13-2018, 07:26 PM   #20
Curtis in MA
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Default Re: Terriable backfiring

With mine it was rust in the tank. Put the filter in the tank and a strong magnet on the outside.
Never has backfired since.
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