on saturday i replaced my 600cfm with a 750 edelbrock carburator(454), drove the car fine all day. sunday i changed the cap and rotor. Monday night i gunned the engine on a freeway on ramp and the car backfired and lost 50% power. now the engine is bogged down and rummbles loud. It backfires out the exhaust as soon as i let off the gas at midrange rpm. It idles okay not erratic or anything like that. Took the distributor cap off and everything looks okay. The timing is fine and do not think it is running to lean. Some thing is definatley wrong. Should i start by putting on the old carburator or dist. cap, rotor? The problem started at once not over a time period. Any help woulf be appreciated. thanks lav

I would start with the wires, a cylinder at a time. If you have points, check the gap, and ensure that the condensor is tight. You might even replace the condensor at this time. While you're in the distributor, check the hold down clamp. Inspect the contacts in the cap and the rotor itself. Carefully inspect the cap for a possible crack. Then move on to the timing, and finally the carb.
It's also possible that you've jumped a tooth on the timing chain.

Take a quick look at the secondary air valve on your AFB, er, I mean, Edelbrock Performer carb. There might be a chance that yours got stuck in the wide open position.

Louie

Turned out to be the carb, put the 600 cfm back on the RAT, uggg. Something broke on my edelbrock 750. Could it be the "power valve" i know next to nothing about carbs, but i do know something poped and made my car run like pooteetang. thanks .

those carbs are simple in design and it sounds to me like you have a small chunk of dirt or teflon tape ? lodged in one of the jets take the top off of the carb and look for debris in the float wells and you will see the jets clean it out and try it again also do not use a screw driver on the mixture screws you will cause perminent damage to the carb turn them in lightly and back out 2 to 3 turns good luck hope I have been some help

I took the carb apart and everything seemed okay, no dirt anywhere. called the seller up and he offered to exchange it for a brand new holley 3310 750cfm.

LavDog, Lost your number, your Emails don't work. Got your bacon in my freezer. Stop by and pick it up!