MG Car Repair: 1978 MGB Distributor cap, dieseling, distributor cap

Question
Hello Howard, David with the dieseling issue. First thank you for the recommendation’s, I will follow them and let you know my findings. I have a question about my distributor cap. When I bought the car I noticed when I replaced the distributor cap that it does not fit 100% proper on the housing. I put the old one on and it fit the same way. It just doesn't seem to seat correctly. Have you heard of this before?  Any thoughts?

Answer
The cap should fit correctly with a "tooth" that locates it in the correct direction and at that time the two clips should snap into place. When installing the cap and you locate it in the "tooth" you should be able to hold it down hard and not be able to rotate it and it should not rock in either direction nor rotate. (providing it still has the Lucas distributor)

I have at times found aftermarket caps that didn't look right so I did another test. I put a small dab of modeling clay (kids toy clay) on the rotor and put the cap in place and then removed the cap to see the clearance between the cap and rotor. A distributor cap can not have anything to do with dieseling though.

Howard