negative air pressure???

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Dec 14, 2006 | 05:54 AM

BIIman

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From: Boca Raton, Fl

negative air pressure???

I have a 3.3 L6 from a '78 Fairmont in my '63 eco/PU everyone helped me decode. Just put an identical new carb on it. It runs fine except for the air pressure hissing and run off when I shut it off. PCV valves need replace or what??? Thanks...

Dec 14, 2006 | 06:59 AM

Jimbare

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From: oklahoma

is it the carb hissing, or something else leaking? seems lke i remember a bunch of fairmonts haveing the "run off" problem. lower the idle, lean it out a little, and check for airleaks!

Dec 14, 2006 | 07:16 AM

BIIman

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From: Boca Raton, Fl

It's the vac line running to the oil filter cap. Since you mentioned it, I'm not getting it to idle down. Thanks

Dec 14, 2006 | 06:17 PM

Jimbare

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From: oklahoma

line from oil filler cap goes to the side of the breather, not the pvc line.

put a straight splice or a new peice of hose on the pvc line and i bet it will run much better!

Dec 24, 2006 | 01:43 PM

Roger Carter

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From: Corbett, Oregon

Run on (dieseling) was a problem with a lot of the 70's cars. Factory cure was to use an idle speed solenoid. The curb idle was set by adjusting this solenoid and not by the "usual" idle speed screw. The idle speed screw was actually a throttle stop. When the engine was "on" there was power to the idle solenoid and when off, the solenoid retracted, allowing the throttle to close, resting against the stop. These idle solenoids were usually an add on part, mounted to a bracket mounted on the carb. The use of solenoids allowed the throttle plate(s) to be open far enough to give an acceptable idle and at the same time letting the throttle plate(s) to close on shutdown, to prevent run on.
Another thought, adding to what Jim brought up. There should not be a vacuum line running to the oil fill cap. The line to the oil cap should be a filtered air line running into the air cleaner. This line supplies clean air for the PCV system.
Good luck,
Roger Carter

Dec 24, 2006 | 01:58 PM

BIIman

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From: Boca Raton, Fl

My real craziness here is I replaced a filthy carb with absolute identical. The only change I did was to leave the automatic choke on the new carb. This is a 200CUI from a '78 Fairmont. Don't know if the choke set-up affects the pressure? Also, when I removed the old carb, there were two(2) carb gaskets. I am only using one new one. I'm trying to think of every angle I can. Thanks

Dec 24, 2006 | 02:15 PM

Jimbare

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From: oklahoma

calm down! itll be okay!
now, get some wd40, or some sort of spray lube. start the motor and spary it around the carb base, and then up around the carb body. if it idles down, you have a vacum leak. make sure the choke plate is open all the way, it will have a fast idle hooked to a rod that will keep it idled way up even if the plate is partialy open.

try that and post back what happens, i will stay on line for a while.

and hey, if it gets to be too much for ya, i will come down and haul it away for you! [heh heh heh, JUST KIDDING!!!!!]

Last edited by Jimbare; Dec 24, 2006 at 02:17 PM.