[as047088]

Any suggestions for replacement carburetor and where to get it. I have a 1968 Firebird with a 1970 400 WS code engine. Installed a Holley 750 spread bore and I'm not happy with the idle. My car is stock and I'm looking for a carburetor that will give it a nice even idle. The Holley Idles like there is a high lift cam in it- uneven. There is a very mild cam in there and when I had the Rochester Quadrajet it idled better but it was shot and needed replacement - What should I get and where ?

David

 

[KeyKeeper]

Sounds like a vacuum leak possibly. I'd spray some carb cleaner around the base of the carb with it running and make sure theres no leaks. If there is you will hear a change in engine rpm.

A holley when adjusted properly will idle like a fuel injected car...near perfect (minus LSA+duration cam lope). Screw the idle mixture screws on the side of the metering block all the way in, and out 1 and a 1/4 turns. Start engine, adjust engine idle speed with set screw on side of throttle plate(throttle stop). then re-adjust mixture screws till idle smooths out. Also look for dripping fuel in the barrels. If you have any, the float level is too high on that set of barrels. Lower the float level a tad to correct.

however, on a pretty stock motor, that carb will probably bit a bit much since it most likely has larger primary butterflies than the Qjet so gas mileage will be reduced in most cases. If you can score a good Qjet then swap them out if you prefer.

Finding a rebuildable pontiac Qjet core seems to becoming more and more difficult. All I ever find are chevy versions.

 

[as047088]

Great ! I'll try it , Thank you.

correction its a 650 cfm

 

[FrankTinCA]

If you want a good rebuilt qjet check with Ken at http://www.everyday-performance.com/. He did a good job with mine, was great to work with and had good prices.

 

[ponyakr]

X2 on the Q. :yes

Everyday has a good rep. According the site, he has an 800cfm '76 Pontiac Q ready to go.

http://www.everyday-performance.com/quadrajet_carburetors.htm#!/Pontiac-1976-Trans-Am-Firebird-400-Quadrajet-17056264/p/46561051/category=578011

These '76-'79 are desirable because they have the APT feature and they are 800cfm. Since you are not running a TH350 Trans, you will not need a Q with the throttle lever which has a provision for the TH350 kickdown cable.

So, that '76 should work for you. BUT, the '71-'79 Pontiac Q's had the big "smokestack" vent, which requires a hole for it, in your air cleaner base. If you don't mind drilling a hole in your base, for the vent, that won't be a big problem. Probably also is a good idea to use a rubber grommet to help seal the vent hole.

If you don't wanna fool with the vent, you can go with a '68 thru early '70 Pontiac Q. OR, you can go with a Buick Q. Everyday has several of these ready to go, in both 750 and 800cfm versions. But, you may have to modifiy your throttle cable hook up, slightly. And, as you can see in the pic linked, the return spring on these Buick Q's pulls from the front, not the rear, like Pontiacs. Some guys are OK with that and some are not.

The 403 Olds Q's also have the APT feature, but without the big vent. And there were lots of 403 Olds engines, in the '79 Birds. So, these 403 Q cores should be easy to find and fairly cheap.

Another consideration is the choke. If you will be needing a choke, I'd consider using a Q which came with a "hot air" type choke, mounted on the side of the main body. With these type, it is easy to replace it with an electric choke. I think Pontiac began using the hot air chokes in '73, maybe. The electric choke can be added by the rebuilder, or you can buy 'em and add it yourself.

Another good Q source is SMI. :smile22:

http://smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100