73 mustang won’t shut off

[Walter1973]

So right now I’m running a 347 out of my 73 mustang. It only sometimes happens but it has gotten worse. Once it has warmed up and has ran for a while I go to shut it off and everything is off but it’s shaking real bad trying to keep turning over. So I have to turn the key back on and try shutting it off a few times before it finally works. It has new wiring, new fuel lines. Only thing I haven’t replaced is the ignition switch, and fuel pump. I’m wondering if it’s the ignition switch. Anyone else run into this issue or know what it might be?

 

[giantpune]

Is it dieseling? Too much timing can lead to that.
High idle speed can do it, too. I have a car that does it, and I'll cheat by turning off the engine while its in gear which adds load to help slow the motor down. Then once the motor is off, put it in park.

 

[cv_72mustang]

Could be the anti-dieseling solenoid. It should cause throttle plates to close completely when ignition is off. Maybe?.

 

[giantpune]

Could be the anti-dieseling solenoid. It should cause throttle plates to close completely when ignition is off. Maybe?.

I assumed when he said an oddball engine size, its already been pulled out and stroked, he's probably running an aftermarket intake and carb. And then the anti-dieseling solenoid would be long gone.

 

[jpaz]

Sounds like you have the throttle plates open to much. Carb needs to be pulled off and reset the plates to have the proper opening of the transfer slots.

 

[Walter1973]

Sounds like you have the throttle plates open to much. Carb needs to be pulled off and reset the plates to have the proper opening of the transfer slots.

I’m coming close to that same conclusion. I am just trouble shooting before actually pulling stuff apart. I screwed myself a couple weeks ago and had to take it somewhere cause my fat grimy fingers managed to pop the distributor out and throw off everything while I was installing a sensor plug.

 

[giantpune]

Sounds like you have the throttle plates open to much. Carb needs to be pulled off and reset the plates to have the proper opening of the transfer slots.

I set the throttle plates and transfer slots adjustment just using a vacuum gauge connected to the ported vacuum. I adjust it so the gauge shows zero vacuum, but it starts to read something as soon as the throttle plates move. Easier than pulling the carb off.

 

[Stanglover]

Believe it or not, it could be fuel. Back when fuel prices went stupid here in Ontario, I thought I'd try to run my 351C4V with 10:1 compression on regular 87 octane, 10% ethanol crap fuel. It would run on it somewhat ok, but when I went to shut it down, it ran on (dieseling). Fortunately I didn't fill the tank, so refilling with premium improved the run-on until it was on full premium. Never done it since, just costs a lot to drive!!
Timing is also critical. I'm not familiar with 302's, stroked or otherwise, but again from my own engine settings, these cars were made to run to emission standards at the time. As soon as we start playing with modifications, it all changes. My car for instance, originally had 6 degrees of initial timing, but as an early 71, only had an EGC on the exhaust manifolds, long gone by the way. After a mild rebuild, actually lowering the compression and with a mild cam upgrade, I now run it at 14 degrees initial and 34 all in @ 3K rpm's. The stock distributor is recurved for only 20 degrees crank timing. The factory setting was 6 initial and 36 all in, so 30 degrees on the crank.
It seems to me that today, people like to go buy those fancy new distributors that are supposed to do it all electronically, so you have no idea what the hell the settings are. A well rebuilt and curved Autolite of Motorcraft dizzy or better yet, a properly tuned DuraSpark will do the job and even look as it should, original.
Or it could just be as others have described. Good luck.

 

[Walter1973]

Believe it or not, it could be fuel. Back when fuel prices went stupid here in Ontario, I thought I'd try to run my 351C4V with 10:1 compression on regular 87 octane, 10% ethanol crap fuel. It would run on it somewhat ok, but when I went to shut it down, it ran on (dieseling). Fortunately I didn't fill the tank, so refilling with premium improved the run-on until it was on full premium. Never done it since, just costs a lot to drive!!
Timing is also critical. I'm not familiar with 302's, stroked or otherwise, but again from my own engine settings, these cars were made to run to emission standards at the time. As soon as we start playing with modifications, it all changes. My car for instance, originally had 6 degrees of initial timing, but as an early 71, only had an EGC on the exhaust manifolds, long gone by the way. After a mild rebuild, actually lowering the compression and with a mild cam upgrade, I now run it at 14 degrees initial and 34 all in @ 3K rpm's. The stock distributor is recurved for only 20 degrees crank timing. The factory setting was 6 initial and 36 all in, so 30 degrees on the crank.
It seems to me that today, people like to go buy those fancy new distributors that are supposed to do it all electronically, so you have no idea what the hell the settings are. A well rebuilt and curved Autolite of Motorcraft dizzy or better yet, a properly tuned DuraSpark will do the job and even look as it should, original.
Or it could just be as others have described. Good luck.

I’m thinking maybe it’s alternator feed back. It has a new carburetor so I don’t think it’s that. Gotta love the trouble shooting after putting everything back together,

 

[Sheriff41]

Either the throttle plates aren't set right or there's a leak in the base gasket and letting in too much air.

 

[cv_72mustang]

Alternator feedback?????

 

[pedstagn71]

Believe it or not, it could be fuel. Back when fuel prices went stupid here in Ontario, I thought I'd try to run my 351C4V with 10:1 compression on regular 87 octane, 10% ethanol crap fuel. It would run on it somewhat ok, but when I went to shut it down, it ran on (dieseling). Fortunately I didn't fill the tank, so refilling with premium improved the run-on until it was on full premium. Never done it since, just costs a lot to drive!!
Timing is also critical. I'm not familiar with 302's, stroked or otherwise, but again from my own engine settings, these cars were made to run to emission standards at the time. As soon as we start playing with modifications, it all changes. My car for instance, originally had 6 degrees of initial timing, but as an early 71, only had an EGC on the exhaust manifolds, long gone by the way. After a mild rebuild, actually lowering the compression and with a mild cam upgrade, I now run it at 14 degrees initial and 34 all in @ 3K rpm's. The stock distributor is recurved for only 20 degrees crank timing. The factory setting was 6 initial and 36 all in, so 30 degrees on the crank.
It seems to me that today, people like to go buy those fancy new distributors that are supposed to do it all electronically, so you have no idea what the hell the settings are. A well rebuilt and curved Autolite of Motorcraft dizzy or better yet, a properly tuned DuraSpark will do the job and even look as it should, original.
Or it could just be as others have described. Good luck.

I have the same problem with 87 octane fuel. I have to run 91 or if no station around has 91 I get octane boost and dump in

 

[will e]

Has OP been clear if it is 'running' or 'dieseling'?

 

[mach1sc]

IF it is dieseling, dieseling is caused by combustion chamber being too hot. as discussed above could be a timing issue, vacuum leak, or just carbon build up in cylinder head . or way way too high compression ratio.