A lot of times the cause for dieseling is too low of octane used. A lot of performance engines require more octane. If you put 92 octane in it, i bet your dieseling goes away.
However, you state it didn't occur with the old carb. My guess is air is getting through somewhere. A vacuum leak, carb gasket leak--something like that is the culprit.
For a quick rememdy, turn ignition off when you are still in gear. It will stop immediately. Then with key half way off (auto trans) put it in park then take key out.
Grab some WD40 and spray around vacuum lines and gaskets with engine idling. Just be careful with the stuff, it is flammable. If rpms go up, you found a leak.
Also, double check your timing and set idle rpms to where they should be--around 750.
SgtDel
aka "Andy"
www.delbridge.net
1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4
Edited by: SgtDel 
at: 2/24/07 7:14 pm
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