My 350's Qjet is running rich, I think my car may have 455 jets instead of 350 jets. 72 GSX tribute convertible Stock 350 no mods 4bbl Quadrajet Auto Trans w/AC
Thanks Larry, your info is very helpful. Do the jets and rods have marking on them to identify their size, I would assume so...
What is the carburetor part number? The original "244" 350 carburetor is a completely different unit than what was used on the 455's. A 350 carburetor with 68 main jets will put down as much fuel as the 455 with larger 73 main jets simply due to the design. Make no comparisons between them when it comes to tuning and jets/metering rods used.......
Cliff, this is a very interesting comment. I converted my '72 350 Skylark from a 2 barrel to a 4-barrel using everything from a donor '72 Buick including a correct 7042244 KC carb. The carb just got a stock rebuild and it runs great in every way except this thing is incredibly rich and STINKS worse than any Q-jet car I've ever owned. It's so rich smelling that I don't even like to drive it. Horrible.
What is your initial ignition timing? Could you be getting nozzle drip? Are the idle mixture needles responsive? If you are using the 1112109 Distributor, and your initial timing is set to 4* BTDC, and you are using ported vacuum to the vacuum advance, that could be causing nozzle drip.
Could you elaborate? Would this be the same in '70 when both were 750 CFM? How about on the 4-sp. carbs (say 7040243/Std. 455 vs. 245/350 manual vs. 246 Stage 1)? I'm no carb expert by any means (your book is on my shelf so maybe someday) but curious since you mentioned this and something I've wondered about. Always appreciate you chiming in on here!
In 1972, Buick 455 carburetors were the larger castings that flowed 800 CFM. The outer venturi was 1/8" bigger, and they used larger jets. The bigger carburetors also had the fixed idle air bypass passages so that the throttle could be closed more yet maintain sufficient idle speed. A common problem with Q-jets fitted to modified engines is nozzle drip. The primary throttle blades are open to the point where the engine no longer is idling on the idle system of the carburetor. The main nozzles start to activate and drip fuel causing a very rich idle. The mixture screws become unresponsive, and there can be a sag/hesitation off idle because the transition from idle to mains is not clean. Using a small block carburetor on a big block can cause this in some cases. If this is what is happening, one way to help it is to increase idle ignition timing so that you can back off the idle speed screw, closing the throttle, and getting the engine back on the idle system. A quick way to do this is to switch the vacuum advance to full manifold vacuum. There will be a noticeable increase in idle speed from the increased timing. That allows you to close the throttle blades by backing off the idle speed screw. From the 1972 Chassis Manual, Cliff will correct anything I got wrong.
If it’s rich at idle you need to look down into the carb and see where the fuel is coming from. If you see it coming out of the booster cluster then that’s the issue, and then this is why. On a Apples to Apples deal the 455 is some 28% bigger CID wise then the 350, this also means it is making 25 to 28% more idle vacuum. The power piston spring that controls the metering rods in the 455 carb is stiffer then the one in the 350 carb. The 350 with its 28% less idle vacuum can not hold the metering rods down in the needed idle position, the result from this is unnecessary idle fuel being seen coming out of the booster cluster.
7042244 KC carb, the correct 1972 350 Q-jet for the automatic. I'm referring to Gary's post #7, NOT the OP. The OP never confirmed his carburetor part number.
"Could you elaborate? Would this be the same in '70 when both were 750 CFM? How about on the 4-sp. carbs (say 7040243/Std. 455 vs. 245/350 manual vs. 246 Stage 1)? I'm no carb expert by any means (your book is on my shelf so maybe someday) but curious since you mentioned this and something I've wondered about. Always appreciate you chiming in on here!" Thru 1970 Buick Q-jets are very similar no matter what engine they were used on. Starting in 1971 the 455 carburetors are different castings and don't share much with the 350 carburetors. The 350 carburetors from 1971-74 are closer to the pre-1971 units as far as components used and how they were set-up. The 244 carburetors stuck with the small MAB's and small upper IAB still in the airhorn, not above the DCR I the main casting. I'm simplifying things but what one needs to remember is NOT to compare the 455 carburetors with the 350 units when it comes to jets/metering rods used. The 244 carbs will put it more fuel with much smaller jets, and more idle fuel with smaller idle tubes/DCR's. The chart for the 1972 units depicts that above.......Cliff
You are most welcome. You'd be surprised how many folks try to tune completely different Q-jets, like a late model on being used on an early application by trying to match up jet/rod sizes with what the early unit would have used. Folks also believe that you have to INCREASE jet sizes for larger engines, any "high performance" engine, or after you've made any intake/exhaust/camshaft changes, etc. In reality the better you do with your engine build and smarter your builder was about parts selection in terms of optimum compression, minimum quench distance, combustion chamber shape, camshaft duration, LSA and overlap the LESS timing and fuel your new build will want everyplace. Not uncommon these days to get on the dyno with one of our builds and only need 28-32 degrees total timing, a slow advance curve and taking fuel OUT of it to get best power. This shouldn't be surprising to many reading this, last time I looked it was 2022 and we've learned a LOT with these sort of things over the past 50 years or so. Even with that said there are still some real "hard heads" out there that think these engines need ALL the timing in right off idle and to throw butt-tons of fuel at them or they woln't run well. I still see folks buying distributor w/o vacuum advance, talk about being stuck in the "stone age".........FWIW......
650 Holley dbl pumper TA intake...cured you can run a 750 but I think the 650 Dbl pump will run a stock 350 just fine, remember it is a dbl pumper. but you Must have a TA intake and NO adapter for a stock 350 intake, it just does not work I run 32* total timing 28* with nitrous
