Since I put the weber on, my car sometimes diesels a couple of times when I shut it off. I put in a colder set of plugs, which has almost eradicated the problem, but it still happens every now and then. Any ideas?

Any of the following will cause Dieseling.

1. Too fast of idle

2. Too Lean of mixture

3. Timing is advanced too far

 

there are a few other causes but those are the only ones I can think of at the moment.

Hmm... I am running my timing at 14 degrees BTDC (stock is 8). But with the ignition off when the car is turned off, it shouldn't affect that. Or does it?

 

Idle speed doesn't seem to affect it.

 

Mixture is possible. I have been tweaking it a bunch to get it to run right, and it could be a bit lean.