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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: ian75c10 on April 19, 2014, 09:05:18 PM
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Mt 75 c10 ( 327 ) runs pretty good but for the life of me I cannot figure out why she fluctuates between 600 & 700 rpm when at idle. I dream of a smooth steady idle and just can't find the problem. Love to hear if others have solved this and how. I have fresh new plugs today. timing is perfect. no vacuum leaks around the carb. Not sure about the intake and also I have headers so could I have a slight vacum leak there? I dont hear any whistling or hissing at idle or driving. I want to say maybe its electrical but i don't know where to start to look. Maybe the dizzy is of or bad? Looking forward to hear some feedback from the pros. thanks guys.
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whats "perfect" in timing?
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With respect to ignition: What plugs are you running? What wires are you running? How old are the wires?
As Irish_Alley asks, what is your ignition timing set at? Where is your vacuum advance connected, manifold vacuum or "ported" vacuum?
What carb is it?
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Sounds like there maybe some clogged air bleeds in your idle circuit in your carb.
What carb do you have?
Vacuum leak was my first thought but you say no, so idle circuit is my next thought.
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Yet another question, do you have a stock cam ?
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How much slop is there between the distributor gear and the cam gear? If the bushings in the distributor shaft are worn, the shaft could be riding up & down. Just a slight lift could cause an advance in timing.
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I have good fairly new MSD plug wires. New accel header plugs. Mild comp cam. 2 month old 600 edelbrock 1406. I have tuned it and retuned it to as perfect as I can get. I am very interested in the distributor comment. Also I do know that before when I let the tank get super low I got stuff in my other carb. That could be a possibility. Would it be a good idea to run some seafoam in the gas tank or would that make things worse?
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Are your plugs gapped? What distributor are you running? What about the cap and rotor? Did you inspect the distributor when you had the cap off assuming you did? You think you got crap in the carburetor why? Do you have a good fuel filter installed? After you verify the integrity of the ignition system, pull the airhorn off of the carburetor, empty the bowls and clean out the jets.
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you have an aftermarket cam and you are bothered by a 100rpm lope at idle?
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you have an aftermarket cam and you are bothered by a 100rpm lope at idle?
As far as I know he never said he has a after market cam. I asked if he had one though and he has not responded yet.
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YES I do have an after market cam. comp cam. 277/282, 470 lift at 50.
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Mt 75 c10 ( 327 ) runs pretty good but for the life of me I cannot figure out why she fluctuates between 600 & 700 rpm when at idle. I dream of a smooth steady idle and just can't find the problem. Love to hear if others have solved this and how. I have fresh new plugs today. timing is perfect. no vacuum leaks around the carb. Not sure about the intake and also I have headers so could I have a slight vacum leak there? I dont hear any whistling or hissing at idle or driving. I want to say maybe its electrical but i don't know where to start to look. Maybe the dizzy is of or bad? Looking forward to hear some feedback from the pros. thanks guys.
YES I do have an after market cam. comp cam. 277/282, 470 lift at 50.
This is why