Preventing Run-On

[Yellow Truck]

The 445 is running very nicely. Idles around 800 very happily, starts easily and the manual choke works very well. It just likes to keep running after I shut it down. I don't have it open too much, so time to try something else.

I know Barry R suggested a solenoid to close the throttle completely, and my neighbour tried to get a shut off solenoid for a Holley (he is the local go-to guy for carb tuning), but the autoparts place never came up with the part.

Looking for a specific suggestion on what part we can adapt most easily for this purpose. I have switched 12v available (unused electric choke wire), and a handy fabricator (my neighbour), just need a good starting point.

[Joe-JDC]

Suggest phenolic or plastic spacer under carb, adjust secondary butterflies slot down a little to decrease idle speed, readjust four corner idle screws to best idle, and make sure the primary throttle blades are closed.  Wrap fuel hose to cool down any heat source to carb fuel.  Joe-JDC

[351crules]

try higher octane,

[Yellow Truck]

Thanks for the suggestions. Have a 1 inch spacer, truck is at a near perfect idle (it has a lot of cam so lumpy as hell), four corners are very even, as I mentioned, my neighbour is Mr Holley here on the island, and I run it on 93 octane, pure gasoline from Chevron.

[390owner]

timing?

[frnkeore]

Since you have a manual choke, have you tried pulling it full on, just before you cut the ignition?

It should cool any hot spots and make it to rich to burn.

[GerryP]

This method will cost you nothing:  If an automatic, leave the trans in gear and turn off the engine.  If it's a manual, leave it in gear and load the engine when you shut it off.

For your electronic method, go to Rockauto and look at a GM idle solenoid for a 1972 Corvette.  Nothing magical about that one.  It's just than I have one and I am familiar with the part.  Alternatively, you can google:  gm thottle idle solenoid holley  You will find both the solenoid and the carb bracket.

[Joey120373]

One trick i used to do "back in the day" when i worked on cars for a living, was to poor or spray water ( with a squirt bottle ) down the carb.

Obviously you have to poor it slowly, keep the trickle of water about the size of one of those little coffee stirrer straws, maybe a little larger. You have to open the throttle a bit while you do this to keep the engine running.

Rev it up to ~1500-2000 rpm and SLOWLY start pouring the water in the carb. This does a great job of cleaning the carbon build up off the pistons and chamber, and usually gets rid of the problem for awhile YMMV.

Just don't be that guy who turns the garden hose on and shoves it down the carb....

[1964Fastback]

I'd suggest ruling out both the ignition switch and fender solenoid first.  It's unlikely but I believe both of these can cause sporadic run on problems if they are flakey.  Does it have an electric fan?  I think under the right circumstances that can back feed the ignition for a second or two under the right conditions.  Again, another long shot.

Pat

[cjshaker]

What Gerry said. Sounds like it's tuned good. Sometimes it's just something you can't get away from completely with a performance built engine. My Mach only does it on warm days and the car is pretty warm, so I just leave it in gear and load the engine when I shut it off (standard). Leaving it in gear in an automatic usually draws the rpms down enough to stall it also.

[Ranch]

Back in the day I had the same problem with over run because to much of the transfer slot is exposed to try to smooth out the idle some (900).  I was doing the turn off as I loaded the engine with the clutch but didn't like that and tried about every thing but drilling holes thru the primary throttle blades, even cracking the secondaries wasn't helping much.  So what worked was the solenoid and I fabed a bracket and that did the trick.  I think the were used on Air Conditioning cars, to step up the idle when the AC was switched on.

[rockhouse66]

The Boss 302 of 1970 used a throttle solenoid.  It had a bracket designed for the Holley carb.  Search for reproductions of these parts and you will have a ready made installation.  Having said that, I also vote for adjusting the secondary throttle plate to close down the transfer slot.

[wayne]

Allstate carb has the solenoid kit bracket and all look under base plates and parts i get all my parts on line from them.

[My427stang]

You need air for run-on to happen.  One technique to counter is to add a little initial, take away a little total in the curve, and close the throttles tighter for the same idle speed.

That being said, the solenoids work

[cjshaker]

Seems like a lot of work and gadgets for something that's easily cured by leaving it in gear..lol  My Dad actually started me doing that years ago, when the gas turned crappy and the older engines were really having issues with stuff like this. Although thinking about it, it may not work as well on an automatic with a really loose convertor.