315C V8 run on when shut off

[digithead]

I did recheck vac at idle yesterday. About 11". I tried both ports on carb. Made diff as far as RUN ON problem goes. I checked for leaks couldnt really find anything. Used carb cleaner spritz as test as welll. Cupped both hands over carb and it stalled pretty quick when starved for air. See pixs. I put on the AC idle solenoid from EDelbrock. Kit is #8059. Pretty pricey for little solenoid. Runs about $160. Simple 12V deal. Apslaply 12V and it extends. Does not have the oomph power I thought it would. I thought when +12 applied it would extend (with engine off key on) and bump up idle. Doesnt work that way. It has enough balls to hold throttle "up" (eg not close all the way) but it cant bump up on its own. So basically you go to key on, usually pump 2-3 times anyways. once you've "pumped' you lifted all pressure off it and its full extended. Then your foots off pedal and throttle arm is in its "idle rest spot" if you will. SUPER EASY to set idle now with 1/2" wrench from drivers side. Can easily do it with air filter on. Much easier then before with screwdriver. When I turn car off solenoid closes throttle slams completey shut and she dies. I got my +12 power for solenoid right of +12 hot of coil nearby. FYI, BEFORE I INSTALLED solenoid, I got bright light and backed the idle stop screw fully out so it was not making contact. So I KNEW that throttle body was fully closed and not getting any air via that path and only mechanical opening movement would ALL be from this new solenoid.

2nd picture shown of course is KEY OFF so no power to Edelbrock solendoid. BTW really well made and super easy to install.

 

[mjlan]

Glad that you were able to solve your problem, that's a very good feeling!

So do you think your issue was that the carb butterflies were too far opened at idle and it was siphoning fuel after you turned off the ignition?

I would have thought that the engine would have to be really hot for that to be a run-on culprit, but maybe your compression is high enough to light off the siphoned fuel.

Interesting.

 

[digithead]

Glad that you were able to solve your problem, that's a very good feeling!

So do you think your issue was that the carb butterflies were too far opened at idle and it was siphoning fuel after you turned off the ignition?

I would have thought that the engine would have to be really hot for that to be a run-on culprit, but maybe your compression is high enough to light off the siphoned fuel.

Interesting.

I literally have to "guess" so. I did not do engine and guy I bought car from didnt know much about what was done when it was rebuilt. its got balls I'll say that. It just seemed any amount those butterflies were open were enough for the run on. I have struggled with it for 3 months now. Reading, tweaking and trying. This was first glimmer of hope. I mean it make sense, you kill power to coil and butterflies snap fully shut. Thats that. No other leaks shes gonna die. Embarrassing as all hell to have this awesome car and pull in places turn it off, and have it bucking and running like a hoopty.

 

[Don C]

At least it doesn't sound like it did the shotgun blast when it died, like John Candy's car in Uncle Buck

 

[71fast]

I installed the same solenoid and that fixed my run on problem. You indicated your solenoid was connected to the coil 12v nearby. There is a 12v plug for this at the firewall and I used that. If you hooked to coil I think it's only around 7 volts.

 

[mach1000]

I had a similar dieseling issue with my 71 mach (restoration in waiting) I tried different carb, dizzy, ignition coil, running type f trans fluid through her to help any carbon build up it might have, adjusting timing etc... Couldn't get it. Would only run on when hot. Pretty embarrassing I might add at the car shows... Never tried replacing the solenoid. I should have. Cars not on the road anymore but will make sure I replace it when it comes out.

 

[Don C]

I installed the same solenoid and that fixed my run on problem. You indicated your solenoid was connected to the coil 12v nearby. There is a 12v plug for this at the firewall and I used that. If you hooked to coil I think it's only around 7 volts.

Good catch. You are correct, the voltage will probably be even less than that, due to the additional load on the resistor wire. It may even over heat the resistor wire, depending on how much current the solenoid draws. This also may be why the solenoid doesn't have enough power to raise the idle.