Dieseling, can anyone help?

Hey everyone, got a question. I have an '89 H.O. switched over to a carb. I used to have a Holley 670 Street Avenger on it, but i could never jet it lean enough, it was always rich. The car always ran great even with it running rich all the time, so i left it on there. For about the last 8 months the damn thing diesels every time you shut it off when it's warmed up. I have just recently put a Holley 600 on it and the plugs are now light brown. I have ran cleaner through the gas and down the carb, but it still diesels, how can i correct this? The timing and idle are all set correct. anyone got any ideas?

I'm currently running 89 octane fuel. My fuel line comes from the pump on the driver side lower front, below the balancer and back up by the alternator, all steel except for the last 6 inches before the carb inlet. My timing is set at factory specs, 10 degres initial and 28 degrees with centrifigal and vacuum advance activated. The car used to run fine with this setup, no dieseling or anything when i first built it. I have rebuilt this motor twice so far, the first time because the oil pump driveshaft gave out on me during a race. Then, about 6 months after the rebuild the thing slowly starts dieseling. I have to use the clutch to kill it everytime now. I think it's just extremely carbond up inside, as it's been running extremely rich ever since it was put together, the plugs have always been black. Now that I got the Air/Fuel ratio correct, i still can't shake the damn dieseling. It's got to be getting ignition from somewhere when i shut it off, the only thing i can think of is carbon deposits in the combustion chamber. thanks for the help so far guys, anyone else got some ideas?

zenboy99 said:

Heres the quick and dirty way I shut my 74 pos Nova off. Put the car in second gear, hold the brake, turn off the car and dump the clutch. May not be great for the car but it works if you're on a date and don't want the lady thinking your car is junk.

Click to expand...

Ya, i already do that....

I would prefer to get it back to normal.