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Old 10-18-2008, 09:25 PM
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Help me 'build' a Q-Jet

I've scored a couple of old Q-jets that are fairly tight still. A little searching on one (7029250) shows that it was used on late 60s 350 - 400 ci Olds.

The second carb is Chev but all the metering parts have been removed, no jets, hangers etc at all. It is also an old pre-emissions unit.

Is it possible to swap all the metering parts from the Olds carb into the Chevy body?

The carb will top a Performer or Perf RPM Q-jet intake, 355 SBC w/10:1, RPM heads and mild (218* @ 0.050") Comp 268 single-pattern cam. 5-spd with some gear.

I'm going to guess that the idle and off-idle should be rich enough without too much tinkering from the vintage they were made but I'm willing to open orifices up if Q-jet gurus have experienced trouble here.

Here's the metering parts within; Q-Jet gurus - are these a good baseline for a hot Quadrajet?

Primary Jet 70
Primary Metering Rod 49B
Secondary Metering Rod AT
Secondary Hanger L

So far I have picked up an Edelbrock accelerator pump for it and a handful of miniscule drill bits. Vizard writes about an orifice in the rear that acts as a pump shot as the 2ndary air door opens - I'm interested in opening that up.

Currently I'm running a Carter clone 600 and the non-adjustable air valve frustrates me.
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Old 10-18-2008, 09:34 PM
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IMHO---The absolute BEST help rebuilding and customizing one of these carbs is to get The Book; Rochester Carburators by Doug Roe--- it's The Rochester Bible.

Good luck
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Old 10-18-2008, 10:34 PM
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Agreed. Qjets changed/improved the guts of their carbs a lot over the years. Jets have to be matched to the rods because of a different chamfer in the jets and a matching taper on the rods. Mix-n-match gets a little hairy without a book to help you through it.
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Old 10-18-2008, 10:58 PM
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I didn't see any advantage or need to move the parts into the Chev body so it can stay on the shelf, no problem there. No need in complicating things further.

I'll stick with the Olds that came complete - I assume that any of the old pre-emissions Q-jets off an engine of reasonable size should be a decent baseline to start with and shouldn't pose any problem feeding a mildly cammed engine?
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Old 10-19-2008, 12:10 AM
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No worries. Those Qjets will support a good bit of HP without being a restriction.

All Qjets are either 750 or 800 cfm, so don't worry until you're hitting the 500+ mark.
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Old 10-19-2008, 12:31 AM
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Let me rephrase that - my concern is maintaining a rich enough mixture for idle and tip-in on a cammed engine, not so much WOT airflow capacity.

I would expect that an emissions era carb would be more challenging to tune with a long camshaft, mine might be borderline.

I think that the torque converter in an automatic trans allows for a more forgiving tip-in, whereas the clutch of a manual trans seems to demand that the off-idle and accelerator shot are 'right on'.

The main reason I'm considering the Q-jet is 'cause the small boosters will probably give a great vacuum signal and come on more smoothly than the Carter design, plus the adjustability of the 2ndary air door.

I'm hoping I don't have to diddle with the carb to get it to work cleanly off idle, that's #1.
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Old 10-19-2008, 01:03 AM
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qjets are very forgiving in that area because of the small primaries. As long as you have the throttles closed enough and you have a good initial timing you should be fine. The idle adjustments are generous and the transition slot is forgiving.

Don't worry about smog-era or not. My favorite Qjet is the 76 and later (non-electric) Qjet. The smog-era carbs might be tuned for conservative emissions from the factory, but they are just as adaptable as any carb.
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