Hey guy i know this is a non-thirdgen question but I need some help. I just bought a 1976 Firebird Formula with a 400c.i. engine and it run like crap. Idle is very choppy and it seem to backfire. What can i do to fix this.

Here are the specs

400c.i. 90° V8
Bored 0.030 over
mild cam 458 lift 218 duration
Pontiac 6X heads
Edelbrock P4B intake Holley carb 750cfm i think.
supercomp headers
HEI vacuum advance distributor w/Points and condencer.


oh, and it has very bad gas. Could this be my problem?

 

I think you answered your own question.
Bad gas, would not be the best combustion wise, leading to failure in normal operation and a bad idle and thru out. Also I would think bad gas would create a type lean condition which will cause backfire.

 

What 400 does it hav in it Pontiac or Chev? If it's a Pontiac, it should have a fairly smooth idle with a cam like that. Check for vaccum leaks, including the power brake booster. That engine will like 8 to 12 degrees of initial timming. And a total of 36 at all in by 3400 rpm. Make sure the pvc valve is working. Make sure intake is NOT leaking. Sounds like you have a lean condition, backfire. Fuel pressure? Float set to low? Has it ever run right?

 

It a pontiac 400, I'm going to check for vacuum leaks today. I car was ran for 2,000 mile on the rebuild until the kid i bought it from got A-rested for no mufflers, then he stop driving it for a year. He said it ran great before it sat so i'm think it's the gas. PCV valve is new, so i'm not worried about that. I'm going to check timing and firing Order today too, you never know it might have crossed wire. Car still has alot of power though, even with it running like crap i still got the tires to spin. That why i thingit more the gas the n anything else.


Robert

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