Here's the deal started with a 2bbl 71 350. Bought a 72 350 4bbl mainifold with a Q-jet. Had the carb rebuilt, manifold cleaned out, added Hooker headers and a Magnaflow 2.5" SS exhaust. Car still is running rough and engine is currently set at about 600 RPM. Tried the old school way of going in with one air/mixture screw on the carb until it got worse then backed off till things evened out somewhat. After swapping things out I DID NOT do a tune up as the plugs/wires/cap(Petronixs electronic guts) were all like new. Any ideas? I was going to do the plugs and cap again but they are not that old. Am I missing something??? Timing is fine!
A big problem I had with a similar project was chasing down vacuum leaks. make sure all tubes are capped or going somewhere. listen and feel for leaks at the carb/intake gasket. (I could hear the sound change as I moved my fingers over the leak point, engine idling). Try plugging the power brake vac line And note any changes. How's the intake bolt torque?
Better yet, get a vacuum gauge and measure vacuum fully warmed up in Park. A stock engine should pull 20"
Asked the guy who rebuilt and installed the carb about any leaks and he said it was all checked. Will check again myself. In playing around with the carb I noticed that I can run the left mixture screw all the way in and the motor won't die. Drivers side is much more sensitive and will shut the car down as I screw it in. It that the way it should be? Ran the car to the local car show last night and she opened up fine when I stepped on her, No dead spot, no hesitation. Still runs rough at idle which I have floating around 600 vs. the 800 she was originally set at.
I'd pull the left screw out and hit the opening with compressed air. Might have a bit of dirt or grit blocking a fuel or air passage. Aerosol carb spray will sometimes work as a substitute for compressed air.
Also check if retaining spring isnt to long.It shouldnt sit completely after the regulator is turned in completely.
If the engine fails to respond to the carb's being leaned out on one side, it is likely that that passage is plugged. This frequently requires disassembly; make sure that the idle passages are clear, I use carb cleaner in a can, and make sure that the passages pass cleaner freely on both sides. That is necessary to assure that the unit will perform when I assemble it. Never fails... ray
If the engine fails to respond to the carb's being leaned out on one side, it is likely that that passage is plugged. This frequently requires disassembly; make sure that the idle passages are clear, I use carb cleaner in a can, and make sure that the passages pass cleaner freely on both sides. That is necessary to assure that the unit will perform when I assemble it. Never fails... Ray
Thanks for the info I wasn't sure if the motor should have died out or not when bottoming out the mixture screw.
It is difficult to predict the engine's reaction to a screw being turned all the way in, but the reaction should be the same on both sides. Something to consider is the pattern of the roughness. If the cylinders not responding to a plug wire being pulled out of the cap temporarily follow a pattern, like 2,4,6,7 it is a carb issue. You can determine that from the air flow in a dual plane manifold. Ray
Was told by the guy who redid my carb that the carb needle valve on the P/S is for the secondaries and needs to be adjusted at 1500 rpm unlike the D/S which is for the primaries and is adjusted at 550-600. Haven't tried it yet though.
No, each mixture needle is for one primary. There is no idle system on the secondary side of a Q-jet. Maybe he meant the fast idle screw on the passenger side choke linkage.
Thanks for all the info guys! JW Guy is actually a nice old gent but I hear what your saying! Unfortunately, I haven't been able to find any good mechanics near where I live. This guy actually came highly recommended. LOL Just want the car to run better and I don't have the time to run back and forth!! :blast:
Steve, You know it really helps when you fill out your profile to include your location. There might be a V8 Buick member right around the corner from you, willing to help, and neither of you would know.
How close are you to Seminole, Florida? George Nenadovich is there http://www.v8buick.com/member.php?u=507 Take a look at his site, very helpful articles http://www.buickperformance.com/page1.htm
Still runs rough at idle which I have floating around 600 vs. the 800 she was originally set at. More than likely one of the idle tubes is plugged, common problem with just about every single previously "rebuilt" q-jet I get in here. The idle tubes should be pulled during rebuilding, as considerable amounts of dirt/debris/corrosion etc can get trapped in and under them. I find it interesting that most "builders" don't even know what they are, let alone how to pull the out of the casting!.......Cliff
