ZZ4 run-on...

4S FED · 03-20-2010, 04:14 PM

Hello all,

I have a 1967 with a ZZ4 crate engine. I'm having a run-on (dieseling) problem. I was wondering if any of you had any ideas of how to stop it.

Here's what I have installed:

ZZ4 350ci GMPP crate engine
Demon carb (crate engine model)
MSD 6AL ignition box
MSD Pro Billet Distributor (tach-drive)
MSD Baster 2 coil
Stock GM (2 wire) distributor
Stock(ish) ignition relay box

I've installed the little capacitor supplied with the 6AL box. I went back and double checked that it was installed correctly (soldered in-line on the green wire (4th pin on the ignition box), and that the line on the cap was closer to the plug going to the alternator). ... This didn't solve the problem.

My timing is set to dead-nutz "0"... should I advance it and see if that helps?

The carb is running a little rich, but all the floats seem to be set properly and the car runs fine....

Any help or suggestions would be great.

4S FED · 03-20-2010, 10:01 PM

Nobody???

warriorp · 03-20-2010, 11:20 PM

less timing and better octane fuel are your typical cures provided there is not a problem with vacuum leaks, carb poorly tuned, etc.

warriorp · 03-20-2010, 11:20 PM

how much total advace are you running on your distributor?

4S FED · 03-21-2010, 01:25 AM

Quote:

Originally Posted by warriorp

how much total advace are you running on your distributor?

The distributor is set on the spring they put in at the factory. They said in the manual it was best for most applications.... I'll have to look and see what color it is.

4S FED · 03-21-2010, 01:26 AM

Quote:

Originally Posted by warriorp

less timing and better octane fuel are your typical cures provided there is not a problem with vacuum leaks, carb poorly tuned, etc.

I'm using Sunoco 93 and have put through several tanks.

warriorp · 03-21-2010, 11:38 AM

double check tdc on the balancer...the outer ring can slip and cause some major headaches...also try a dial back to zero timing light...set on 32deg total advance...remove vacuum advance hose bring engine up to full advance (typically 3500rpm) and line up timing marks...good luck!

08 Crystal Red · 03-24-2010, 02:46 PM

Some others things that might come into play---

Fast idle
Overheating
Carbon deposits

Hope it all gets worked out!

4S FED · 03-24-2010, 04:59 PM

Checked the timing and it was 3deg retarded.

So, I went in steps, upping the timing until maximum vacuum was gained (about 15 inches at idle). Ended up with just a little over 9deg of advanced timing. Runs fine now (quite a bit more power too!

)

08 Crystal Red · 03-24-2010, 06:17 PM

Quote:

Originally Posted by 4S FED

Checked the timing and it was 3deg retarded.

So, I went in steps, upping the timing until maximum vacuum was gained (about 15 inches at idle). Ended up with just a little over 9deg of advanced timing. Runs fine now (quite a bit more power too!

)

I'm glad to hear that -- since my ZZ4 is due in about two weeks!