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#1
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QuadraJet - Which primary metering rods are stock for #7042210?
I'm considering changing the primary metering rods on my rebuilt '72 Chevy #7042210 650cfm QuadraJet on my 400ci and I'm wondering what the stock metering rod number is for my carb?
The secondaries are DA rods (which are stock) - easier to pull out and check vs. the primaries. I'd like to know the stock primary rods as I want to order a few new ones before I pull the top off to see how they perform at my altitude (~5,800 ft). Thanks! Jim.
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' |
#2
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There was never a 650 Quadrajet. Most were 750 or 800. Yours is likely a 750? Not trying to sound like a Beavis...
You need to call Cliff, if you don't have any parts on hand. Www.cliffshighperformance.com he cal sell you any parts you may need, AND sell you the parts needed for today's blend of gasoline. Tell him I said hi!!!
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#3
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From factory the 1972 Chevy Truck 350 #7042210 Quadrajet has #74 primary jets and 43B primary rods.
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#4
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Quote:
Big thanks to Mr. Tom Vaught! Jeff
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Carburetor building & modification services Servicing the Pontiac community over 25 years Last edited by shaker455; 11-13-2022 at 06:26 PM. |
#5
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Yes, but that formula assumes that the carb was jetted right for the motor it’s on, but at a lower altitude.
We don’t even know what cid motor the OP has this carb on no less. Also if the OP has this carb on a 350 ( actually a 354 cid stock) it has to be taken into account that the stroke of a Pontiac 350 is a heck of a lot more then a Chevy 350 and this produces a much earlier demand for air and in turn fuel for any given rpm . I might be more inclined to first change out the power piston spring to a lighter one then to change rods. If it where my car I would get a set up in the exh system to check out what the air to fuel ratio is now then to potentially put the motor into a pinging of Knock condition while checking out metering rods.
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I do stuff for reasons. |
#6
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Thanks everyone, good feedback! Note that the specs for my 400ci are in my signature, fyi. In my research years ago on my #7042210, I read it was 650cfm. It's actually good to know it's most likely a 750cfm.
My mechanic built the carb back in 2008 and it's been installed since and has performed very well over the years, but I'm investigating if I can improve the performance even more since I don't believe it's ever been set up for altitude. I confirmed the secondaries are indeed DA rods (stamped and I measured them), but I have not yet confirmed the primary rods nor the jet size currently installed as I wanted to gather some details first to see what to order and have on hand before I opened up the carb. I'm guessing that since the secondary rods where stock DA rods, the primaries will also be stock (43B.) Next I'll check out Cliff's site to see what's available...
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' Last edited by tremo; 11-13-2022 at 09:06 PM. |
#7
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Very few Chevy smallblock Quadrajets flows full 750 cfm, most of them are restricted by the reduced air valve opening degree.
Only some HP units got the full 750 cfm flow. I wouldn't count on there being original jets and rods if the mechanic who fixed the carburettor was knowledgeable. These carburetors have .120" main air bleeds in air horn and floatbowl and the mixture would be too lean with the original jetting. One way to still use the original jetting is to reduce the main air nozzles with .050" inserts. Otherwise, #77-#78 jets paired with 48B-49B primary needles may suit your engine's needs with this carburetor. There's only one way to know what's inside (or two if the mechanic has notes). FWIW |
#8
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Keith, my thinking was that the carb repair person has ground down the air flap arm to allow it to open fully.
In my salvage yard endeavors, I bought a couple of 301 Q-Jets. The secondary air flaps on those, barely opened at all!!!
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#9
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Quote:
- If most don't flow at 750cfm, what do you think they actually flow at (approx)? ~700cfm? - You make a good point not to assume what the primary metering rods and jets are. My mechanic was a Pontiac-guy, so he may very well have set it up for my altitude? I was also thinking they might be stock because it's always run very rich at idle even after adjusting the idle mixture screws properly. I will see about opening the carb to check. - Thanks for the recommendation to use #77-#78 jets paired with 48B-49B primary needles. This input is what I'm ultimately after! FYI that the car is primarily a street car, but over the last couple of years I've started to race the full season for my class (about 7 times/year) so I'd rather tune it for racing vs. street. - So the idea is to increase the jet size (more fuel) and decrease the metering rods (less fuel)? I'm still learning how the jets work in conjunction with the the metering rods so bare with me! Note that while I live at 5,800', Bandimere is typically at ~9,000'+ density altitude during the season and even higher during 90+ degree days. Would your recommendation change given the higher density altitude? Thanks again for all the input, very valuable!
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' Last edited by tremo; 11-14-2022 at 04:32 PM. |
#10
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Quote:
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71 GTO, 463, KRE 295 cfm heads ported by SD Performance, RPM intake, Qjet, Dougs Headers, Comp cams HR 246/252 ...11 to 1 , 3.55 cogs, 3985lbs.....day three- 11.04 at 120mph ....1.53 60', 6.98 1/8 mile |
#11
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Before you make any big changes to the carb contact me at the shop. I've tuned thousands of Q-jets for high altitude use. On that unit it is best to replace the factory APT screw with one of my external screws for easy access. Teamed up with the correct jets and metering rods you will find it easy to dial in for your application. The factory APT screws in those can a bit difficult to remove but it is LIGHT YEARS better to use that system than to pull the top on and off the carb to make metering changes for part throttle A/F.
You actually got lucky with the carb choice. It's too lean right off the bench with the stock jetting, plus we typically add 5-7 percent more fuel when using this currently avalable fuel. So if you factor in that plus the altitude you really aren't off that much. It's probably a little "fat" at WOT with DA rods in it, but being too rich is ALWAYS better than too lean and never results in putting a few pistons in the oil pan!........... https://cliffshighperformance.com/
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
#12
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Thanks Cliff!
I popped the top off the carb today and learned I have .042 primary rods and #74 jets. As per Kenth the stock set up for my carb is: Quote:
Perhaps this is too rich for my altitude (+9,000' density altitude)? Would Kenth's recommendation be something to try: Quote:
Thanks for any advice!
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' Last edited by tremo; 11-20-2022 at 09:23 PM. |
#13
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Quote:
Wouldn't I want to decrease the jet size like to a #71-#73 while also increasing the rod diameter from .043 to .048-.049 to lean it out? Thanks!
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' |
#14
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The best way to tune that carb for what you are doing is to employ the APT system in the baseplate. I make an external screw for those to replace the factory one. Then you can simply fine tune the part throttle A/F for altitude without having to take the top off the carb and change parts......
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
#15
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Quote:
For now, can you make a base recommendation for a primary metering rod and jet size for my altitude (+9,000')? I was thinking of going from .042 to .045 (45B) and jet size from #74 down to #72. Secondary rods would remain at .0443 (DA). This seems to me like a good place to start (without going too lean) and would give me something to try in the interim. Thanks again!
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* '69 Custom S - 2dr Hardtop Coupe - Rust-free Oregon survivor with all original panels and original trunk floor * Engine alive and kickin' March 2nd, '06 * RA-IV 'spec' 400 (.060-over = 410ci), balanced, Comp Cams #9794041, #16 heads (72cc converted to large valve) with 1.65 Harland Sharp Rollers * QuadraJet #7042210, HEI, Hurst V-Gate, FlowTech Headers, X-Pipe with dumps, Flowmasters, TH-350, 3.90 Posi * Best ET: 14.06 - Bandimere Speedway, CO. @ 5,800+' |
#16
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The APT set-up is easy but in some cases that original APT screw can be difficult to remove. I'm able to get most of them out, but once in a while run into one that's not coming out despite your best efforts.
I'd start there. Remove the cap over it, use plenty of penetrating oil and some heat from underneath from a propane torch. Once it's out contact me at the shop and we'll cut right to the chase for tuning parts.....
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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