Rochester QJet Conversion

[Guest John Chapman]

I've long been planning to put a Carter AFB/Edlebrock on my 300, but after reading the QJet article on Buick Street, I'm wondering.<P>Does anyone have experince with the QJet on the 300/340 and what are the thoughts?<P>Cheers,<BR>JMC

[Guest]

the carter will get worse mileage, but it will be easy to get running right. <P>Your would probably need a dyno to really tune a quadrajet, they are really precise and tricky. Thats why they get good mileage and thats why people give up on trying to tune them.

[Guest]

Use a Q-Jet and send it to John Osborn in KY for setup. It's what I plan on doing once I get some added funds and downtime. Tom's right tho, most ppl give up on tuning them. I almost did.. :-)

[NTX5467]

Depending on whether the engine you have is stock or otherwise, the smaller AFB would be a good option. BUT getting it to run lean enough might require some "playing with it" time. I perceive that the stock jetting will be for a more performance-oriented (i.e., richer) calibration than for a basically stock situation. I might be wrong in that presumption, though. I suspect the smaller version would be more applicable to your engine size also.<P>The QJet is an extremely "tunable" carburetor. It was used on everything from 230 cid Pontiac OHC inline 6 cylinders (circa '66) up to 500 cid Cadillac V-8s with the basic 750 cfm configuration. If you will read the H.P. Books "Rochester Carburetors" publication, it details all of the "ins and outs" of calibrating QJets--complete with jet and metering rod and power piston spring and secondard metering rod hanger GM part numbers and specifications. <P>I suspect that if you can find an original QJet from a later '60s Buick 350 with an appropriately matching intake manifold (some of the earlier ones had heat tracks as the Chevy V-8s did, I believe) and carb base gaskets, it might put you pretty close to where you need to be. Or at least get the rod/jet/spring specs so you can duplicate them if you buy a rebuilt carb with undetermined jetting in it.<P>At certain air flow velocities through the primaries, the QJet is very efficient compared to other carbs, but the key to any carb is having it correctly calibrated to your application.<P>One area I would favor the AFB would be in ease of changing the metering rods. One small screw and the metering rod/power piston is in your hand. Compare that to what it takes to get to the same place on a QJet!<P>As far as spread bore carbs go, my personal favorite is the Holley #9895 model of 4175 series vacuum secondary carb. It originally was the '79 Chevy L82 spec direct OEM replacement carb but has now been spread across more Chevy applications. I know that it works as I've had one on my Camaro 305 for several hundreds of thousands of miles. Electric choke and all of the hookups too. It's a little pricey, but I found the best price on <A HREF="http://www.racesearch.com." TARGET=_blank>www.racesearch.com.</A> I suspect it might work on your Buick application with a small amount of adapting in the linkage area. I offer that as an option of a new carb that might be an "out of the box" bolt-on situation.<P>Of course, if you desire a basic OEM look, the AFB (with the upper ID band removed) would be the closest thing. Be advised that there are Edlebrock versions of the AFB and there are also some Federal-Mogul AFBs too. Federal-Mogul is who bought the original Carter Carb operation, for what it's worth.<P>Just some thoughts . . .<BR>NTX5467