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I'm looking for some help and suggestion as to my problem with my Carburetor. I have a 69, 350 L46, 4 spd. with a Quadrajet. Not sure of the history of the carb but I'm sure it has been rebuilt once or several times. The problem I've noticed is that the idle is about 900 (high?) unless I "blip, quickly punch," the gas pedal and then it drops by about 200 rpm and stays there. I'd like to get the idle down lower than the 900 and I wonder why it only drops when I do the blipping thing?
This occurs when the car is up to running temperature and the choke is off and fully open. The idle speed adjusting screw is backed off. Have tried different accelerator return springs but it makes no difference All linkage is clean, tight at the bracket and smooth in its operation. Other than the high idle the car runs good and shows no signs of problems because of the carb.
I suppose my questions are why it doesn't idle below 900, and is there any thing I could try? Perhaps a Lars rebuild may be the only answer but I fear that previous work done in the past might not make that a possibility. Thanks and take care.
HI your engine is getting too much air. I am not a certified person to give advice, but the simplest logical reason I know is your choke is not adjusted well. The choke is still keeping your throttle plates open too far until your blip the throttle. Then the choke linkage drops away from the throttle linkage letting the idle drop further to 700. Your choke has an adjustment that needs to be checked. Hot rod magazine August 1986 has a comprehensive article on the Q Jet and adjustments.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by mbp
The problem I've noticed is that the idle is about 900 (high?) unless I "blip, quickly punch," the gas pedal and then it drops by about 200 rpm and stays there. I'd like to get the idle down lower than the 900 and I wonder why it only drops when I do the blipping thing?
There are two common problems that cause that issue, especially if the carb has been "rebuilt" or commercially "remanufactured:"
Primary throttle shaft bushing sloppy and worn out. If the shaft has excessive play in the throttle plate on the driver's side, the shaft can "****" in the bore and cause a slight misalignment of the throttle blades in the throttle bores when the throttle is gently closed. "Blipping" the throttle allows the throttle blades to center themselves and the shaft, and allows a return to normal idle.
Primary throttle blades not properly centered in the throttle plate bores. If someone, like a commercial builder, has removed the throttle blades for whatever dumb reason, they seldom spend the time to get them correctly and accurately aligned upon re-assembly. If the blades are not in the perfectly-centered position, engine vacuum will pull the blades into a bind against the sides of the throttle plate bores, and return-to-idle will be erratic. "Blipping" the throttle, again, momentarily unbinds the blades and allows the throttles to fully close.
Either problem requires that the throttle plate be removed from the carb. If the throttle plate requires a bushing, this requires some special tooling and parts to repair.
Post a couple of photos of the carb and I may be able to tell you if you have a hacked commercial carb that may have other significant issues.
Lars
From: At my Bar drinking and wrenching in Lafayette Colorado
Mike was unable to get his photos loaded here on the Forum, so here are the photos of his carb:
The carb is a 1969 L46 (350/350) carb. It appears to be in good shape, but it has been commercially rebuilt as evidenced by the "t-bar" pressed into the bowl vent in the choke rear wall casting. It's also evident that the commercial builder sandblasted and stripped all plating off the steel parts - the parts are all bare steel, which is typical of a commercial rebuild. Also notice how they painted the choke pulloff diaphragm - all give-aways of a commercial job. That said, it is highly likely that the carb has multiple issues and problems, not just limited to the misaligned throttle blades. I have sent Mike a copy of my "Commercially Rebuilt Q-Jet Problems" paper so he can get an idea of many of the issues that are most likely present in that carb.
On the good side, his carb does not appear as badly hacked as many that I've seen. I can see that his secondary linkage is misadjusted, which could prevent opening of the secondaries under some conditions. It may have some issues internally, and we know they screwed something up on the throttle plate assembly. Bottom line is that the carb needs a complete teardown and inspection to determine all the issues, and then they need to be properly and correctly repaired and resolved.
Lars
Mike was unable to get his photos loaded here on the Forum, so here are the photos of his carb:
The carb is a 1969 L46 (350/350) carb. It appears to be in good shape, but it has been commercially rebuilt as evidenced by the "t-bar" pressed into the bowl vent in the choke rear wall casting. It's also evident that the commercial builder sandblasted and stripped all plating off the steel parts - the parts are all bare steel, which is typical of a commercial rebuild. Also notice how they painted the choke pulloff diaphragm - all give-aways of a commercial job. That said, it is highly likely that the carb has multiple issues and problems, not just limited to the misaligned throttle blades. I have sent Mike a copy of my "Commercially Rebuilt Q-Jet Problems" paper so he can get an idea of many of the issues that are most likely present in that carb.
On the good side, his carb does not appear as badly hacked as many that I've seen. I can see that his secondary linkage is misadjusted, which could prevent opening of the secondaries under some conditions. It may have some issues internally, and we know they screwed something up on the throttle plate assembly. Bottom line is that the carb needs a complete teardown and inspection to determine all the issues, and then they need to be properly and correctly repaired and resolved.
Lars
hi Lars , This is not my carb but I want to personally thank you for helping many of us on this forum
Mike was unable to get his photos loaded here on the Forum, so here are the photos of his carb:
The carb is a 1969 L46 (350/350) carb. It appears to be in good shape, but it has been commercially rebuilt as evidenced by the "t-bar" pressed into the bowl vent in the choke rear wall casting. It's also evident that the commercial builder sandblasted and stripped all plating off the steel parts - the parts are all bare steel, which is typical of a commercial rebuild. Also notice how they painted the choke pulloff diaphragm - all give-aways of a commercial job. That said, it is highly likely that the carb has multiple issues and problems, not just limited to the misaligned throttle blades. I have sent Mike a copy of my "Commercially Rebuilt Q-Jet Problems" paper so he can get an idea of many of the issues that are most likely present in that carb.
On the good side, his carb does not appear as badly hacked as many that I've seen. I can see that his secondary linkage is misadjusted, which could prevent opening of the secondaries under some conditions. It may have some issues internally, and we know they screwed something up on the throttle plate assembly. Bottom line is that the carb needs a complete teardown and inspection to determine all the issues, and then they need to be properly and correctly repaired and resolved.
Lars
hi Lars , not my carb but I want to personally thank you for helping many of us on this forum 👍
Q Jet question
