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I received this from John Johnson. He's a real GTO guy...very involved in the GTOAA
and widely considered the premiere Judge guy around. Anyway, I sent an e-mail to
John asking about carb stuff - specifically the fact that he's looking for carb id#
7041263 - which is the carb that I have on my '71 4 speed. I thought that his
response was really interesting. He really knows his stuff!... Leonard Good to hear from you. : Sounds like you have a nice car!! We have 2 goats, a '69 HT Judge and a '70 GTO conv (took it to the Nats in Wichita and had fun with it in the Popular Vote class and cruised the town with it! You probably read about our trip in the convention issue of The Legend). Yes your 7041263 (there are a few other #s, too) flows more than then any comparable Pontiac Q-Jet (except the '73-74 SD-455 Q-Jets). If the regular ones flow 750 cfm then you are probably near 800. Look inside the primary bores- yours has a "single-booster-ring" in each primary throat. All other Q-Jets have a double-ring. The lack of the 2nd ring lessens the obstruction of air flow, so at a given suction, it does probably flow a little more. PMD tried this in '71 only. Most people say they idle worse than any other Q-Jet, and couldn't meet the '72 emissions changes so they went back to 2 rings. The '73-4 SD-455 Q-Jets had a bigger primary throttle bores for more air flow, but kept the 2 booster rings. I have no idea why yours runs badly when you get on it. When you say adjustment screw, could you mean the air valve? There's a "vacuum pot" that tries to hold the air valve closed when you're at a high vacuum condition, like idling or light accelleration. When you mash it, the vacuum drops, the pot can't keep the air valve closed, and it drops open, allowing air thru the carb and thru the bottom throttle plates to make POWER! With the car running at idle (have someone hold the brakes on) take the air cleaner lid off and try to push the air valve down (open) it should resist but you should be able to move it and the car will probably try to die. If you can't open it, shut the car off and try to open it. See if you have a mechanical binding problem or what..... also the 2nd-ary rod hanger should rise up as the air valve comes open. This brings the 2nd-ary metering rods up and allows fuel flow for the secondaries. It the rods don't come up, no fuel flows...... With a good light (Car 0ff) hold the air valve open, and have the friend push the gas pedal down and hold it. Hold the choke open and look to see if the primary throttle plates are completely open and point straight up and down. Do the same (look thru the air valve) at the 2nd-ary throttle plates. Not quite sure how you adjust the primary plates if they don't completely open, but the 2nd-ary ones have a adjustment rod on the driver's side rear bottom of the carb- you should be able to figure out how to bend it to get the throttle plates straight up and down (allows full flow). Also check to see if the throttle cable travel is full enough to cause a wide open carb condition. John J |