got this from another site:

reasons for dieseling:
1 idle speed to high
2 ignition timing incorrect
3 incorrect spark plug heat range
4carbon build up in combustion chamber
5 valves sticking
6 bcdd or ficd system not operating correctly
7 valve clearance incorrect
8 intake air leak
9 egr system not operating correctly
10 fuel shut off system not operating correctly

1986 Montero 2.6l
31X10.5 BFG MT - Weber carb with custom intake
Rear LSD - RCI seats - Oil cooler - Manual hubs
Custom bumpers front and rear + rock sliders