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Thread: the infamous rough idle question!!

  1. #1

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    the infamous rough idle question!!

    Ok, so I am curious as to what causes a carburated engine to idle differently when it is cold OUTSIDE, and Idle completely different when it is warm OUTSIDE. My truck idles perfect when its like 58 degrees or colder outside, as soon as the temp outside gets above like 58 it idles really low and sorta rough. It does this regardless of the engine temp, only as a result of the outside air temp. What would cause this?

    ** I have a aftermarket air cleaner installed. its just a chrome circular one, which means the air cleaner no longer has the tube from the heat shield on the exhaust manifol putting hot air into the air cleaner assemby.**

  2. #2



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    Could be the choke is sticking mostly closed, but open enough to give it decent airflow. the open air cleaner is helping to mask the problem in the cold weather, by leaning it out.
    Pennyman1
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  3. #3

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    is there a way to adjust the choke? I know i have a throttle postion screw, a idle adj screw, and my air/fuel screw. adjusting those is about all i can do on a carb!... lol... when i rebuilt my engine, we took it off, and my buddy started stripping it down, cause he KNEW what he was doing, but i quickly learned he did not, when he we turning it around in his hand half taken apart, and had the what the hell is this look on his face.

    **UPDATE**
    I might have fixed this issue.... somehow my fuel/air mixture screw had vibrated all the way loose, and was just kinda sitting there, not sure how it didnt fall out! So i put it back in readjusted it, idle, distributor timing, runs stable.... for now.
    Last edited by Ram50Man; 04-14-2011 at 07:22 PM.

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    I'm glad to hear you fixed the problem. The only thing I know about carbs idle is what I experienced on my truck. The idle quality is lower when you have a vac leak. My truck had other problems with it like a coolant leak and a bucking between 2.5k and 3.5 k rpm. Might have been related, but I wanted to swap the motor to get rid of the headache of a learning experience and just drive it.

  5. #5


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    Quote Originally Posted by 4doorciv View Post
    I'm glad to hear you fixed the problem. The only thing I know about carbs idle is what I experienced on my truck. The idle quality is lower when you have a vac leak. My truck had other problems with it like a coolant leak and a bucking between 2.5k and 3.5 k rpm. Might have been related, but I wanted to swap the motor to get rid of the headache of a learning experience and just drive it.
    great choice...:D

    ram50man
    yeah glad to see you getting it fixed...

  6. #6

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    i think its fixed, took it on the freeway for a short 5 miler test, seems to be ok now. Still going to have the problem again if i cant get a retainer spring or something to put in there, cause it will just keep vibrating back out.

  7. #7



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    use blue thread locker on it - it will stay in place but can be moved without major effort.
    Pennyman1
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  8. #8

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    very good advice.... is Blue Thread Locker the brand?

  9. #9



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    Permatex is the brand - any parts store will know it by blue thread locker
    Pennyman1
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  10. #10

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    Quote Originally Posted by pennyman1 View Post
    Permatex is the brand - any parts store will know it by blue thread locker
    Sweet, thanks. I will have to go grab some tomorrow.

  11. #11


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    +1 on that thread lock. The red is a medium strength and the blue should work for your application. I used the stuff at work and on my car/truck.

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