I have an '85 GT that I put a GT-40 crate engine in. It originally being an EGR car, I initially retained the EGR plate, etc. I put a Road Demon 625 on the car, but quickly realized this was too little of a carb (wouldn't idle down, ran rich, etc. due to cam overlap). It ran fine at speed, accelerated fine, even ran great at full throttle once I put a different (lower tension) vacuum secondary spring in it. But, it still wouldn't idle out, and I felt there was more in the engine. So, I replaced it with a new Speed Demon 650 with special jetting precisely for this engine and combo. It's a mechanical secondary carb, so I had to remove the EGR plate for clearance issues. I left the EGR-compatible Edelbrock intake on the car, but blocked off the port in the carburetor mating base with a plate. Now, the car backfires like a bean-fed donkey under light to moderate acceleration around 2800 rpm. If I floor it then, it accelerates like a scalded cat, but driving it around is plain embarrassing with the backfire problem. Is this related to capping off the EGR port? If so, I'll order a different intake and do away with it. I've adjusted everything else in the system; timing, vacuum reference, idle mixture screws, float levels, idle transfer slot settings, you name it. Any carb-savvy gurus out there with a suggestion, or better yet a fix? 
Carburetor / EGR / Intake Issues
- Thread starter bt15
- Start date
-
Sponsors (?)
Which edelbroock manifold did you use? Is it by any chance the 3721? I don't mean to be an a$$, but if you do decide to change manifolds can I buy this one off you?
As for you problem I don't know why blocking off the egr port would cause the car to be backfiring. Are you sure that your timing is correct?
As for you problem I don't know why blocking off the egr port would cause the car to be backfiring. Are you sure that your timing is correct?
It is the 3721, but I think I'll keep it even if I try the other manifold out. I don't see what would cause the backfire problem from the intake, either, but stranger things have happened. My real concern is that it didn't do this before replacing the carb and removing the EGR plate. But, then I can't really test with it due to the clearance issues. Maybe it's an advance issue. The distributor may be getting a different read from this carburetor / plate setup. I can try that, too, I guess. 
Similar threads
