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Statcoy

Well-known member
Joined
Dec 1, 2019
Messages
57
Reaction score
1
Location
Oregon
My Car
302 1971 Mustang Coupe
Just tryna restore it
So I was messing around with the project car and the alternator light was wasn't really paying attention and I startrd the mustang up and I went to turn the key off and it was still running it tool a good 30 secs to turn off. Never really had to deal with this before, so I really do not know where to start on this. I have not turned it on since! 71 Coupe 302 if that matters. Thanks

 
Was it running because the power did not turn off or because it was dieseling, running from heat in the cylinders?

Some of the cars have a solenoid on the carb that closes off the throttle plates completely to cut the air flow off to prevent dieseling. If the car has carbon build up in the cylinders that can cause it to diesel. Check with your auto parts store and see what they have for putting in gas or pouring down carburetor while running. Short runs and no extended runs on interstate build up carbon. Also pull spark plugs and look for carbon build up on tips. I bad replace or clean.

 
Was it running because the power did not turn off or because it was dieseling, running from heat in the cylinders?

Some of the cars have a solenoid on the carb that closes off the throttle plates completely to cut the air flow off to prevent dieseling. If the car has carbon build up in the cylinders that can cause it to diesel. Check with your auto parts store and see what they have for putting in gas or pouring down carburetor while running. Short runs and no extended runs on interstate build up carbon. Also pull spark plugs and look for carbon build up on tips. I bad replace or clean.
Im pretty sure the power did not turn off

 
Ignition switch sticking or not adjusted correctly.

The other possibility is the starter solenoid is sticking, keeping the "I" terminal on the solenoid hot. That's easy to check, disconnect the "I" terminal wire, start the engine and then shut it off. If it shuts right off with the wire disconnected the solenoid is your problem, if not I would start with the ignition switch. I would try it a couple of times with the wire connected and with it disconnected. It might be an intermittent problem.

When was the last time you had it running?

 
Ignition switch sticking or not adjusted correctly.

The other possibility is the starter solenoid is sticking, keeping the "I" terminal on the solenoid hot. That's easy to check, disconnect the "I" terminal wire, start the engine and then shut it off. If it shuts right off with the wire disconnected the solenoid is your problem, if not I would start with the ignition switch. I would try it a couple of times with the wire connected and with it disconnected. It might be an intermittent problem.

When was the last time you had it running?
You might not be able to start the car without the I terminal wire attached to the starter solenoid.  Better to keep it attached, then start the car, then remove the wire from the starter solenoid, then turn the key off.  If the car continues to run, the ignition switch is probably faulty; it is stops immediately, the starter solenoid is bad.

 
Did it continue to run at a full idle, or was it dieseling? If dieseling, is mentioned, carbon may be a culprit. However,I have also observed that incorrect idle speed along with insufficient ignition timing is also a common cause of this. Were you doing anything, or have you done anything recently that would result in increased idle speed and decrease initial timing settings?

 
Ignition switch sticking or not adjusted correctly.

The other possibility is the starter solenoid is sticking, keeping the "I" terminal on the solenoid hot. That's easy to check, disconnect the "I" terminal wire, start the engine and then shut it off. If it shuts right off with the wire disconnected the solenoid is your problem, if not I would start with the ignition switch. I would try it a couple of times with the wire connected and with it disconnected. It might be an intermittent problem.

When was the last time you had it running?
Ok for sure Ill check the solenoid! And I've I only started it up a handful of times , it idles super high where I'm kind of scared it'll blow up or something . I'm assuming the carb needs to be tuned but I've never tuned any carb and it doesnt have the original Holley

 
Did it continue to run at a full idle, or was it dieseling? If dieseling, is mentioned, carbon may be a culprit. However,I have also observed that incorrect idle speed along with insufficient ignition timing is also a common cause of this.  Were you doing anything, or have you done anything recently that would result in increased idle speed and decrease initial timing settings?
It idled how it regularly does which is really high. And the only thing I've done was have someone clean/rebuild the carburetor. I'm like 99% sure its not tuned

 
Did it continue to run at a full idle, or was it dieseling? If dieseling, is mentioned, carbon may be a culprit. However,I have also observed that incorrect idle speed along with insufficient ignition timing is also a common cause of this.  Were you doing anything, or have you done anything recently that would result in increased idle speed and decrease initial timing settings?
It idled how it regularly does which is really high. And the only thing I've done was have someone clean/rebuild the carburetor. I'm like 99% sure its not tuned
I want to be careful to say this is not the only reason a car might diesel - I am not an expert, but have dealt with this, so this is just based on my own experience.

You may want to try looking into proper idle and timing settings. Your engine specs (ie, camshaft duration, compression, etc) can play a role here. Fora mildly built  engine, I try to get into the 600-800 RPM range and anywhere from 14 to 20 degrees initial timing - engine specs will influence this, so knowing what you have under the hood is helpful.

I had dieseling issues with my 79 corvette after building a stroker.  I had 1025:1 compression and the cam was about 230+ degrees @.050. Once I got it to idle at 800 RPM and set the timing to about 20 degrees initial, that went away. No pinging at cruise, the engine seems to like it.

IF you go this route, only make small changes and check the result. If possible, try test drives not just start it up. I would reset your idle speed, then go cautiously with timing, especially with the timing. Start conservative with the timing, and just bump it up maybe 2 degrees at a time until the dieseling stops. Pay attention to total timing at around 3000 RPM, you probably don't want to go more than 36-38 (not counting if you run a vacuum advance). More efficient heads can lower this total advance, so these are things you will want to make sure you know about your engine.

If you have a really aggressive cam, you will probably need more timing to get it to idle at lower speeds. If this is the case, this can also help low-speed drive-ability.

Then make sure you don't experience any detonation (pinging) at cruise. You may find it helpful to incrementally drop idle speed as you advance timing, but I prefer to get one where you want it and try to tune the other till you solve the problem.

Just  one approach to consider - if you are not sure what you have under the hood, make sure you do a bit of research first.

 
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