Why's it doin this?
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New User
Joined: Apr 2006
Posts: 14
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Why's it doin this?
Hello all, I'm a newcomer with not a whole lot of mechanical know-how, I recently bought a 72 f250 with a rebuilt 390 in it. She runs strong, even though she's a gas hog, but she just started doing something funny. When I turn the key off, the engine turns off, but sputters a little bit, sometimes for 20 or 30 seconds, as if there was still spark and gas going into the cylinders. I know that's not normal, what can I do about it? A friend suggested rebuilding the carbs, is he correct?
Elder User
Joined: Dec 2003
Posts: 610
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From: socal
It's called dieseling or run on I think it has to do with timing. Is it running hot? How long ago was it rebuilt? the distributor may be in wrong(I know I always had a hard time with that) I am sure by this weekend you will have plenty of responses from knowledgable people so hang in there help is on the way!
Senior User
Joined: Nov 2004
Posts: 223
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From: Yelm,Washington
I think it has to do with carbon build up in the head chambers and/or on top of the pistons...This carbon glows red hot while your engine is running and when you turn off the ignition it acts as an ignition source for residual fuel/air...Atleast thats what I have been told...I believe there are products on the market that will help remedy this..One is called "sea foam".. Sold a NAPA...Pour about 30% in your crank case. Pour the rest in the fuel tank.Run your engine for twenty minutes then change your oil and filter...Amazing how much black carbon will blow out thru the exhaust..Worth a try anyways.
Posting Guru
Joined: Jul 2003
Posts: 2,222
Likes: 1
From: East Central Florida
wulfage,
1st
Welcome to the information bank on FoMoCo F series trucks here at FTE 
Assuming you do not have the premium fuel version of the 390 FE engine running 87 octane fuel;
1 Turn your Idle rate down a little.
2 if you have a dashpot on the linkage make sure it backs off at shut down,
3 check & reset your timing at the OEM Spec.
4 check for vacuum leaks or a cracked/ bad/ loose vacuum line.
If that doesn't rectify the problem, check your centrifigul advance weights in the "dizzy" to make sure they are not hanging and/or do not have a fatigued/ broken return spring[s].
If none of these help get back to us and we'll come up with more things to check out
FBp
1st
Welcome to the information bank on FoMoCo F series trucks here at FTE Assuming you do not have the premium fuel version of the 390 FE engine running 87 octane fuel;
1 Turn your Idle rate down a little.
2 if you have a dashpot on the linkage make sure it backs off at shut down,
3 check & reset your timing at the OEM Spec.
4 check for vacuum leaks or a cracked/ bad/ loose vacuum line.
If that doesn't rectify the problem, check your centrifigul advance weights in the "dizzy" to make sure they are not hanging and/or do not have a fatigued/ broken return spring[s].
If none of these help get back to us and we'll come up with more things to check out
FBp
Last edited by FordBoypete; Apr 14, 2006 at 07:33 PM.
