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Old 01-20-2003, 09:14 PM
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Hey guys. I have been racking my brains trying to figure out my rochester Q-jet. I recently rebuilt the carb. Now the engine runs like crap, but when I open the secondary valve towards the rear of the carb the rpm's rise and it sounds cleaner. When the secondary is closed the engine bogs down. What I do not understand is how do the secondary valve open on its own.. there is no linkage to operate. The only way I can get it to open is by hand. Totally lost. Please help. Thanks

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Old 01-20-2003, 09:25 PM
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the secondaries open by an air valve, the fact that your engine runs better when they are slightly open indicates either bad idle circuit or the rods aren't in the jets, making for rich fuel mixture, sticking power enrichment system?
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Old 01-20-2003, 09:50 PM
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How does the air valve actuate the butterfly valve? Where should the valve be at idle and at higher rpms?

Thanks
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Old 01-20-2003, 10:24 PM
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The secondary baffle acts like a Holley vacuum secondary. It only opens as engine demand increases and it is difficult to do that bt popping the throttle inh te shop. Only way to get them to work is under load so you can't see it. As BOB says, your problem is in the primaries, not in the secondaries. You are running rich so the problem is either metering rods or idle circuit. Jan 2003 Rod & Custom magazine has an article on Q-jets that may answer your questions.
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Old 01-21-2003, 04:47 PM
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I am going to disassemble the carb tonight. I had a mechanic tell me to check the needle or metering rod for correct location. Can you damage the metering rod by putting it into the wrong spot? Will the airhorn even fit onto the main body if they are not in their correct spots.

thanks for all the info so far. You gauys are awesome.
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Old 01-21-2003, 05:31 PM
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Wait, whoa, stop! Before you take the carb apart again, lets get a little scientific and check some things. There is a vent tube near where the air cleaner stud screws into the carb. At the bottom of that "vent tube" is where the power valve is located. "Fashion" a paper clip with a "T" on the end and place it inside of that "vent tube". With the engine off, notice the amount of paper clip that is sticking out of the vent tube. Are you with me so far? Anyway, when you start the engine the paper clip should sink about a quarter of an inch because the power valve has been sucked down with manifold vacuum. Incidently, you can gently push the paper clip down into the vent while the engine is off and you'll feel the spring action of the power valve. Ok, back to work. Start the engine again and this time quickly give the engine alot of throttle by hand and if everything is working ok in the power system, you'll notice the paper clip move higher because the vacuum is less because you BRIEFLY gave the engine full throttle. If you don't understand what I mean then by all means forget what I said because I don't want you to get hurt revving the engine too high. Just bring your credit card with you and go to Pep Boys! Oh yes, one last thing. Do your idle screws effect the idle when you turn them in or out? If you find that you can turn the idle screws in all the way and it still runs then look into the primaries with a flashlight and with the engine IDELING look for fuel "dripping" down. That means the float level is too high. There are a couple of other checks but lets see how the above checks go for you and please, be careful! Good luck
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Old 01-24-2003, 09:53 AM
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Great info. Everything works as you described. I believe float level is too high. It was the only thing that I really drastically adjusted. I thought I had done it to specs, but I guess not. B4 I take it apart this time, anyother suggestions? Thanks again.
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