73 pontiac question - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 5 (permalink) Old Apr 15th, 02, 07:35 PM Thread Starter
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Hi, I have a question about a 73 formula 400 I acquired. (this is funny since I have a 73 camaro, but the firebird seemed like a great deal)

The engine's history is mostly unknown to me but i'm having a bit of a problem. Here are the specs as far as I know:
for sure: 400 pontiac, edelbrock perfomer intake, perfomer 1411 electric choke carb, hooker heads, mallory distributor, dual loud flowmasters

possibly: lunati cam, specs unknown. There were a ton of lunati cam stickers on the car but I dont know if its whats in there. The guy I got it from didnt know either. He gave me an edelbrock cam and lifter set with the car that apparently the owner before that used for a while but removed for unknown reasons, and replaced with the old cam. Also supposed .030" over, I dont know the rebuild history or mileage tho.

The engine tends to backfire/pop (mild backfire) through the carb under part throttle conditions, load, or first pushing the gas. Its especially bad if the motor isnt fully warmed up, the car will usually die. It starts right up, idles, and seems to run decently, revs up in park with usually no backfiring at all. I have noted a quick ticking noise coming from what would be the number 4 chevy cylinder (dont know the numbering system for pontiac).

First thing I suspected was some sort of carb problem, and I found that the square bore carb was on a spreadbore intake. Fixed with an adapter.

I read a lot from searching about a ton of different things that could cause symptoms like this, but I wanted to see if anything sounded really obvious, and also to get a checklist of the most likely things that could be wrong. Anyone else had any sort of experience with these pontiac motors?

thanks

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73 Camaro, 350 .030" over, and 450 HP
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post #2 of 5 (permalink) Old Apr 16th, 02, 01:06 PM
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Don
 
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Sounds like you have a cam going flat.

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post #3 of 5 (permalink) Old Apr 16th, 02, 02:34 PM
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Mark
 
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I second the cam lobe going flat.

-Mark.
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post #4 of 5 (permalink) Old Apr 16th, 02, 06:21 PM Thread Starter
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would it make sense for it to be the cam if the ticking is only coming from one side?

perhaps a bad lifter or broken valve spring? could this cause this intake backfiring?
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post #5 of 5 (permalink) Old Apr 17th, 02, 07:21 AM
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Don
 
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Any of those could cause the problem, also those Poncho motors have been known to pull out the rocker arm studs...

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