I'm looking at getting a new carburetor for the 350 im my Chevelle. I currently have a 650 cfm Holley double pumper, it has been rebuilt and worked on to try and get rid of a gas leak that won't go away and since being rebuilt it has not run the same so instead of throwing money into this carb I'm looking at replaceing it with a new one. I'm considering another 650 cfm double pumper since it ran good with it and I got six years of use out of it with out a peep or maybe trying a Holley 670 cfm street avenger carb, I've heard good things about them but I'm unsure if a 670 will be to big,. Heres the spec sheet on my motor, it has an Edelbrock performer intake, a complete MSD ignition and Hooker comp headers, thanks for any help or suggestions.

http://www.jasperengines.com/performance/classii3.pdf

Where is it leaking gas? Seems like it would be much cheaper to fix the old carburetor.

First it was leaking from the front fuel bowl then the rear then the diaphram was replaced then it was rebuilt then it had a new rear fuel bowl installed now it has a slight leak around the carb spacer (possible blown gasket?) if the engine is not started in two days. I have enough money in this carb to have already bought a new one and have plenty left over. I want to take a sledgehammer to this one, I don't want to waste any more money and time with this one, I've read on here once you start messing with a Holley they are never the same again.

I've heard that about Qjets,but never a Holley,not enough parts to mess up, I've brought some pretty corroded Holleys back from the dead to work fine. You say leaking around the spacer? below the throttle plate? I assume that you have the float level set correctly.

the throttle shafts leak alot on the older holley carbs.......the front shaft has no "seals" it is just two machined surfaces once they wear out they would need (carb base) drilled out a resleeved..........the rear have seals and they can be replaced......in most carb kits i have used the seals are the round white curled up seals.....not sure if they are made out of teflon or not.....they look like white plastic rolls......those take car of the secondary throttle shaft leaks........

this could be your problem.....all other leaks would be from improper gasket placement when it was rebuilt.......there is very few parts to the holley carb....and can be tuned alot easy then most on the market as far as i'm concerned.....

670 wouldnt be to big....depending on how stout your motor is.....i have always used the 750 holley on the 350's i build for friends or myself.......in the past when doing test and tune at the track....the 750 came out on top as far as e.t. and mph went......i did a back to back one year with a 650 double pumper and 750 double pumper and the 750 stayed on.....the car was running mid 14's at 90 some mph....others have said you get better throttle response from a smaller carb but to me the track times tell me which is better......for me a 750 is the carb on the 350 sbc with any little hop up goodies on it........if its stock or very close to it......then stay with the smaller carb.....