Catalina Backfire

918 Views 10 Replies 5 Participants Last post by Mertz, Jun 22, 2009

Mertz

Discussion Starter · Jun 11, 2009

I have a 66 Catalina with a 69 428. I just installed the Pertronix ignition and converted back to a Qjet from an AFB. I always have had some popping out of the tail pipe. It was good for parades to rev the engine and hear the following pops. Now it pops when I hit the gas. The wires are in correct order. The timing is correct as far as I know. There is no indication of valve problems based on the vacuum gauge. Could this be lean conditon?

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cobalt327

· #2 · Jun 11, 2009

Mertz said:
The timing is correct as far as I know. There is no indication of valve problems based on the vacuum gauge. Could this be lean conditon?

Retarded timing will get you backfiring on deceleration, no doubt. You should put a timing light on it to know exactly what your timing- both initial and total- is set at.

Check the plugs after a run to see what they tell you AFA the carb being lean.

Be aware that some non-diagnostic type vacuum gages are damped to keep the needle from fluctuating- exactly what you DON'T want when diagnosing an engine. Be sure your gage is one meant for the purpose. Because a valve sealing or cam lobe problem could be at the root of it all.

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riceharvester

· #3 · Jun 12, 2009

Mertz said:
I have a 66 Catalina with a 69 428. I just installed the Pertronix ignition and converted back to a Qjet from an AFB. I always have had some popping out of the tail pipe. It was good for parades to rev the engine and hear the following pops. Now it pops when I hit the gas. The wires are in correct order. The timing is correct as far as I know. There is no indication of valve problems based on the vacuum gauge. Could this be lean conditon?

Its the carb. Swap back and see what happens....

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Mertz

Discussion Starter · #4 · Jun 12, 2009

I have set the timing with a timing lite. I am thinking now that the damper might have slipped. I will check for top dead center and make sure it is correct. The manual calls for 8 BTDC if it is a low hp motor and 12 if it is high hp motor. I have it set as high as I thought was ok. I had some popping out of the tailpipe with the AFB as well. It didn't happen while hitting the gas however. The AFB was a 650.

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JackHandy

· #5 · Jun 12, 2009

Set your timing to 8 BDTC.... I know everyone want's to pretend they have a race car...

But your in diagnostic mode...so stop pushing the envelope until you know everything is working perfectly in a standard state....give yourself a solid starting point before you start making adjustments.

Set your timing back and make sure your carb is setup correctly as well.

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cobalt327

· #6 · Jun 12, 2009

Mertz said:
I have set the timing with a timing lite. I am thinking now that the damper might have slipped. I will check for top dead center and make sure it is correct.

Good idea to check the outer ring on the damper. :thumbup:

Were you able to determine that your mechanical advance is working? As in- the timing advancing with the engine speed increasing, w/the vacuum advance disconnected?

Is the vacuum advance working and hooked up?

There's a tutorial for making a timing tape HERE that you can use to see what your total timing is at, in case you don't have access to an adjustable timing light.

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Mertz

Discussion Starter · #7 · Jun 13, 2009

I have an adjustable timing lite. I restarted it today and it is running better but now it is backfiring and afterfiring. I have been using regular gas and might try some octane booster. I might have some water in the gas from sitting this winter. Carb is set at 2.5 turns out.

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jimfulco

· #8 · Jun 16, 2009

How old is the gas?

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Mertz

Discussion Starter · #9 · Jun 16, 2009

That may be the problem. I had older gas in it for a few years but have since added new gas (last fall). I am using regular with 10% ethanol. I am going to try adding some premium or toluene.

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cobalt327

· #10 · Jun 16, 2009

Mertz said:
That may be the problem. I had older gas in it for a few years but have since added new gas (last fall). I am using regular with 10% ethanol. I am going to try adding some premium or toluene.

I would stick to premium. It will be as good as it needs to be, short of good ol' 100 octane from "BITD".

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Mertz

Discussion Starter · #11 · Jun 22, 2009

I added toluene to the gas and tried tuning it again. I discovered that my Qjet doesn't have a vacuum port that doesn't have manifold vacuum at idle. Disconnecting the vacuum advance the base timing was at 4 BTDC. With vacuum it was at 10. I am reading about 15 in of vacuum. I tried setting the timing by vacuum and managed 17 but but that put the readings of the mark on the balancer. It ran better and no backfire or afterfire when I rev'd it. The idle would drop off quickly if I retarded it past a certain point. The was a small range that it ran well in. The cap and rotor are new. I thought I had solved the problem until I got in and rev'd the thing with the pedal and the backfire and after fire were back in a big way. Vacuum is steady but I still think it might be valves.

The Qjet in one made by Carter that starts with 170. (I forgot to bring in the number this morning) Is something wrong with the carb if it doesn't have a port without vacuum at idle. There is no choke on it so I rigged a manual choke of the lever on passenger side. The engine starts good. but had a bit of trouble with the restart after the timing change indicating I went to far. I set it back a little and it started better.

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