Fuel Pump spacer

[reddog]

I have a glass bowel pump on my M38 I am guessing it is off of a CJ? I was going to run it until I find the proper pump. Does this pump require a spacer or not?

Thanks Bruce

[wesk]

The M38 pump installation requires the spacer. The larger diaphragmed and heavier sprung dual vacuum pumps load the cam more than the smaller single diaphram pumps. Basic physics makes it very clear that the closer to the fulcrum's (pump lever) pivot point you move the cam lobe the greater the pressure on the cam lobe. Hence the spacer. There are several thicknesses of spacers used across the Willys dual diaphragm pump equipped engine models. They determine the output flow of the pump and using the correct spacer is necessary for the carb used on that engine model.