run-on?
Junior User
Joined: Jun 2002
Posts: 67
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From: SpringfieldMissouri
run-on?
my 78 400 did the same thing but worse it would stop dieseling unless i let out the clutch in geer (thats bad on it) so i just played around with the adjustment screwes on my carb a little bit and tuned it down and it wont diesel anymore but sometimes it will if i dont tap the gas pedal and make the idle go down a little before i shut it off
New User
Joined: Jun 2003
Posts: 15
Likes: 0
run-on?
on carb engines carbon build up on the valves would cause your problem after running and getting hot the carbon would get hot enough to fire the cylinders. i know this will sound crazy to everyone but you could pour a 12 oz can of water thur the carb to clean the valves. you have to keep the engine at a high rpm and pour the water slow but it will do the job. i have done my 96 f150 this way i used a sprayer it works good.but i would check my timing first and for bad gas if the timing and gas are ok the water will do the trick. my father worked for a auto dealer ship this is where i leaned to do this they done this real often. but like i said keep the rpms up and pour it slow.
Upper Case Edited Out by FTE
Upper Case Edited Out by FTE
Last edited by Gwrenchplus; Jun 17, 2003 at 08:06 PM.
Postmaster
Joined: Jun 2001
Posts: 2,809
Likes: 3
From: Loveland, CO.
run-on?
Yeah, GW has an old trick there. We used to do that, although I never tried it for a run-on problem. They say that transmission fluid works too. I remember once, I had someone keep my car running while I poured a quart of tranny fluid in the carb! I don't know if it did anything, but it sure made a lot of smoke!
New User
Joined: Jun 2003
Posts: 15
Likes: 0
run-on?
transmission fuild works but it takes more of it and having to put up with all the smoke but water is best. carbon will also cause a engine to ping like the timing is off when under a load.
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Elder User
Joined: Sep 2002
Posts: 503
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From: Edgewood, NM
run-on?
Thanks for the responses! I will start with the timing and go from there, I have a feeling that is probably the cause.
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Posting Guru
Joined: Sep 2002
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run-on?
I have an easy solution. Get that engine up to red line. Drive it hard like that for a day!! That will always shoot that carbon out of the tailpipe.
No, seriously. When I bought my 1990 Bronco it had sat for a long time in the garage. It still had the original engine when I bought it. I did replace it for a bigger one later on though!! $8,000 worth of big engine.
Anyway. I put the truck in park. I ran the RPM close to 5500, for about 2 seconds!! I did this three or four times. When I got out of the truck. The tail pipe had shot out a bunch of black carbon chips!! It ran better after i did that!! That's my 2 cents!
No, seriously. When I bought my 1990 Bronco it had sat for a long time in the garage. It still had the original engine when I bought it. I did replace it for a bigger one later on though!! $8,000 worth of big engine.
Anyway. I put the truck in park. I ran the RPM close to 5500, for about 2 seconds!! I did this three or four times. When I got out of the truck. The tail pipe had shot out a bunch of black carbon chips!! It ran better after i did that!! That's my 2 cents!
Posting Guru
Joined: Aug 2000
Posts: 1,984
Likes: 2
run-on?
Shane, your 78 should have had an idle control solenoid on it from the factory. It allowed for a normal idle when the engine was running, and then closed the throttle when the key was switched off. This prevented the run-on.
If yours is gone, you can get another one at a parts yard. Another solution would be to advance the timing slightly (thereby reducing the throttle opening at idle), and leaning out the idle mixture screws as much as possible.
If yours is gone, you can get another one at a parts yard. Another solution would be to advance the timing slightly (thereby reducing the throttle opening at idle), and leaning out the idle mixture screws as much as possible.