Idles high, why?
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Idles high, why?
My 79 2wd has a rebuilt 2150 motorcraft carb. Starts up first turn of the key, warm or cold, drives really nice, no flat spots but it idles really high. If I stop the truck, leave in gear with engine running and take my foot off the brake, the truck will drive forward, not a little, a lot ! Even after the engine is hot, its runs fast. Same in reverse.
I checked the curb idle screw and its almost out so thats not it, I need to check the fast idle setting per other posts in the forum but want to get advise on what could cause it to run fast when warm?
I checked the curb idle screw and its almost out so thats not it, I need to check the fast idle setting per other posts in the forum but want to get advise on what could cause it to run fast when warm?
More Turbo
Joined: Apr 2007
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From: Salisbury, PA
I am familiar only with Holley's but what comes to mind is to check how far open the primary butterflies are at idle. You may have some adjustments wrong that will not let them close the whole way. Possibly electric choke connection adjustment?
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From: Jordan Station, ON
+1 on this... Also, on my carb I have an electronically controlled diaphragm that's designed to reduce the amount of wear caused by the butterfly when it's closing by making it close slower. When I have that hooked up, it doesn't close all the way and the butterfly stays open all the time, causing high idle, so I don't use it.
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Yup, I will start with fast idle but before I adjust, which direction is rich and which is lean? The choke housing doesnt have a mark so I assume perpendicular is middle?
I dont think the fast idle is dropping through the cam as expected so I'll set tomorrow am when cold and then follow the steps per manuals etc.
I dont think the fast idle is dropping through the cam as expected so I'll set tomorrow am when cold and then follow the steps per manuals etc.
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From: Jordan Station, ON
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I think its the other way assuming you face the carb from the right side of the truck (also based on a 2150 carb pdf doc I found)
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Ok so I started the truck this am no issues, got it up to temp and pumped the throttle, no change, then I forced the fast idle cam to the next level and the revs dropped to where it should be. Killed the engine and tried to figure out why, never adjusted anything now it wont start. Give it an hour to cool down and will try again but why wont the cam drop when the accelateror is pumped?
I have 2 service manuals open, plus multiple forum posts and im bloody dumbfounded.
I have 2 service manuals open, plus multiple forum posts and im bloody dumbfounded.
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From: Jordan Station, ON
Oh, sorry... I'm thinking of my 1bbl YFA from facing forward (behind the carb)
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No worries, confirmed with a post by fmc400 on here.
Finally I find out whats happening, engine hot and running, its on fast idle and I pump the accelerator but the lever doesnt hit the cam to move to the next level so the revs drop. If I manually force the cam it drops. If I then pump the accelerator it resets to high fast idle again.
I see it but no idea how to fix it.
Update, some screw (kickdown screw?)between the choke and the carb, so I tweaked it and when pumped the gas, it stayed on idle. Yippee. Now to wait till it all cools and see if it sits on the cam high and then when warm pump da gas, see what gives
Finally I find out whats happening, engine hot and running, its on fast idle and I pump the accelerator but the lever doesnt hit the cam to move to the next level so the revs drop. If I manually force the cam it drops. If I then pump the accelerator it resets to high fast idle again.
I see it but no idea how to fix it.
Update, some screw (kickdown screw?)between the choke and the carb, so I tweaked it and when pumped the gas, it stayed on idle. Yippee. Now to wait till it all cools and see if it sits on the cam high and then when warm pump da gas, see what gives
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