Thread: Dang SBC won't stop!

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Hey Guys, I have an interesting problem, I hope it has happend to others so someone can explain it to me.

My small block chevy won't stop running, I know that happens sometimes to motors (detonation) but this thing is like "possesed". As for the internals of the motor I can't say. I got the SBC cheap and I was hoping it would do for a while till I build something else. At present it only has headers on it with about 3 foot of pipe. Once I start it it runs a bit rough but it still runs ( I haven't started tuning yet). Here is the fun bit
I turn off the key.....It runs
I unplug the power lead to the HEI.......It runs
I isolate the battery IT STILL RUNS.
I stick my hand over the carb and choke it to death....IT STOPS.

What is causing this?
Thanks
Andy.

What's your idle speed, Pickle??? You might have to put one of the idle shut down solenoids for A/C cars on it, when it's powered it will hold the idle at the correct RPM, when power to it is cut off (by the key) it lets the throttle plates go full closed.

That's it Denny, go to your room !!!!!

The Idle throttle jigger sounds interesting....I hoped it might be any easy fix....no more laughing Denny..!!

If only it ran without fuel....

I think it has pretty high compression, I am only saying that because the guy i bought it from said so.

Andy

yup, IMO it's one of the few parts that chebbierlay ever came out with that actually worked !!!!!

But whats actually making it run-on.....?

Is it hot spots in the head mixed with high compression "dieseling" the motor?

Does this suggest a problem with the motor?

Andy

i've had this problem before. put a different alt on or replace the diode in the one you have. what happens is when you turn the key off the alt will not shut off because the diode is not working and the current is backfeeding through it and therefore you alt is keeping the whole thing going. the only thing that doesnt make sense is that you said that you unplugged the dist and it still did not shut off, not sure but i think that should have killed it. next time just unplug your alt and see if it quits, if it does- bingo.

Thanks guys.

could be electrical, usually just a case of the throttle blades not going full shot and allowing fuel to be drawn thru the idle circuit.

Posted by gherkin:
"I unplug the power lead to the HEI.......It runs"

This is a dead giveaway that it's not alternator feedback, it's hot spots in the chambers and the throttle blades being cracked open a hair at shutdown. It's getting fuel and air from the slightly open blades and ignition from the hot spots.
Fixes:
1. Advance the timing a little.
or
2. Adjust the throttle blades to completely closed. Mount a 70's GM dashpot at the throttle lever so that when the dashpot gets 12v ignition juice, it opens the throttle blades to the idle position, otherwise, without any juice the dashpot is dead and the throttle blades are competely closed. The motor CANNOT run on without fuel and air.
or
3. take a friend and a gallon of water to a secluded area. With your friend on the accelerator to keep the motor revs up, pour the water down the carb throat (not too much or you can hydraulic the motor and break things). Feed it all you can without killing it with your buddy workin' the pedal at about half-throttle. You won't believe the crud that comes out the tailpipe, so be sure and don't do this in a congested (with people) area.
or
4. Shut if off in gear.
or
5. All of the above.

Yet again You guys Rock!

Closed up that pesky holley butterflys and the liitle bugger stops like a champion.

Next stop twin Strombergs! Just finished assembling them and should be putting them on this weekend. The gasket kits came from MACS Autos and I found only one small gasket missing from one kit, I suppose thats pretty good. Have had worse.

Andy.

dang, i was wrong again