Won't idle when warm.
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Won't idle when warm.
I've got a 73 F250 with a motorcraft 2100 on top of a 390. Runs great when cold but won't idle when warm. As long as you are on the throttle it stays running but wants to die once stopped. So far I have replaced plugs and wires, fuel filter, fuel pump, timing is set at 12* (I've advanced it trying to find a sweet spot but that didn't work either), pulled all vacuum lines one at a time found nothing. With a vacuum gauge hooked up it it jumps between 12 and 14 in/hg at idle and stays steady at 22 with acceleration. I've tried propane to find a leak as well as wd40. I'm not sure where to go from here. Did I miss something simple?
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The choke is working, when the plate opens that is when the stumbling of the idle starts. I haven't thought of an internal leak. I bought the truck about 2 months ago, the carb has a remanufactured tag on it from about 8 months ago. I haven't gotten into it too much other than maling putside adjustments. Mixture screws are out 3.5 turns, started at 2 turns out but would not idle.
Postmaster
Joined: Mar 2011
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From: Taxachusetts
Your vacuum readings at idle suggest you're between 4000 - 6000 feet in elevation...
"Normal" engine vacuum readings should be 17 - 21 inches Hg at idle, at sea level......presupposing the engine is in fairly good shape.
If you're sure your carb is not the culprit and vacuum leaks cannot be found - as in brake booster, booster check valve, brittle/cracked vacuum lines and even the vacuum advance can (the diaphragm can go south and cause a vacuum leak) - I might consider incorrect valve timing (timing chain has too much play), ignition timing is too retarded, vacuum leaks (again), poor compression.....not to mention yer plug gaps being correct and points (if you have 'em) not being timed right - dwell....
Whatever is easier to check for you....mebbe the carb first as mentioned above, then a compression or leak-down test.
"Normal" engine vacuum readings should be 17 - 21 inches Hg at idle, at sea level......presupposing the engine is in fairly good shape.
If you're sure your carb is not the culprit and vacuum leaks cannot be found - as in brake booster, booster check valve, brittle/cracked vacuum lines and even the vacuum advance can (the diaphragm can go south and cause a vacuum leak) - I might consider incorrect valve timing (timing chain has too much play), ignition timing is too retarded, vacuum leaks (again), poor compression.....not to mention yer plug gaps being correct and points (if you have 'em) not being timed right - dwell....
Whatever is easier to check for you....mebbe the carb first as mentioned above, then a compression or leak-down test.
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
That's a lot of turns out for a "re-manned" carb. Have you checked for vacuum leaks at the throttle plates? Also, how many turns out is yer curb idle screw? The reason I ask is if the transition slot is open too much, you're into the main circuit and not the idle....which will cause idle speed/mixture problems as well as vacuum leaks.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
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From: NorCal
Check fast idle cam setting when warm. It should point to the stamped "V".
Check float level.
Choke piston sticking.
Missing gasket between the choke housing and the carb. It's supposed to seal a vacuum passage.
Yer vacuum is low.
Check float level.
Choke piston sticking.
Missing gasket between the choke housing and the carb. It's supposed to seal a vacuum passage.
Yer vacuum is low.
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Postmaster
Joined: Sep 2013
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From: Pasadena, Ca
Your PVS may not being opening or closing when it should. You won't find that vacuum "leak" with propane.
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Freshman User
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I had taken it off to plug the port to isolate the booster. I've got a new line and clamp for it. The fitting on the tree for that line is actually about 2 inches long!
Postmaster
Joined: Sep 2013
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From: Pasadena, Ca
