Need some carb help

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Feb 15, 2011 | 05:45 PM

MikeKrock

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Need some carb help

I can not seem to get it to idle correctly...have a 79 with 302....after inspection it looks to me like the throttle solenoid is either not working or not set up correctly. With the throttle at idle I thought the solenoid would be in contact wioth the throttle...there is about half an inch of space even with the solenoid plunger fully extended.

What am I missing?

Feb 15, 2011 | 06:39 PM

rdweathers

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From: Florida

I think the solenoid in question will only increase the idle when the AC is on, this is the way mine is set up. There is an idle adjustment screw on the carb it self near the base plate.

Feb 15, 2011 | 09:58 PM

fmc400

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From: Austin, TX

Quote:

Originally Posted by rdweathers

I think the solenoid in question will only increase the idle when the AC is on, this is the way mine is set up. There is an idle adjustment screw on the carb it self near the base plate.

Incorrect. On these era engines, the solenoid is not related to AC as was the case for later years. This is a common misconception. If yours is set up that way then it was modified at some point.

This solenoid is called an "idle stop solenoid." This solenoid is powered from hot-in-RUN, meaning it's powered (and engaged) the entire time the engine is running. When the engine is running, the idle speed is maintained by the solenoid - meaning the throttle tab should rest on the solenoid plunger. When the engine is shut off, the solenoid retracts, and the throttle plates are allowed to close (almost) completely. This was done to prevent dieseling on later model smog motors that tended to require a higher idle speed, yet ran at hotter combustion chamber temperatures (which is the perfect recipe for dieseling).

On this kind of setup, the idle speed is adjusted by a long screw that moves the entire idle stop solenoid bracket toward and away from the throttle stop. With the engine OFF and the solenoid retracted, the throttle plates should be able to nearly close. You don't want them to close completely, otherwise they will bind in the throttle bores. Instead, adjust the standard curb idle screw (on the carburetor base, driver side) so that with the solenoid retracted, the throttle plates are open ever-so-slightly.

Feb 23, 2011 | 12:51 PM

MikeKrock

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If I understand this correctly the solenoid plunger should be touching the throttle plate when the engine is off and cold..since it is not I should use the long screw and move the entire assembly until the plunger touches the plate.

Thanks for your help.