willysmjeeps.com

Hi I have the correct military fuel vac pump on my M38. For a bit of fun I mounted a see through fuel filter so I could see the fuel flow through and was surprised how little fuel flows into and out, obviously enough as she keeps running.
So I connected the outlet on the pump to a pressure gauge and found it produced 4.5 PSI which according to TM 9-8012 would be correct.
Then I applied pressure with my mouth to the pump outlet as I read you should not be able to blow down the line, again all good I could not.
The instructions on the pressure gauge said the pressure should hold on the gauge for a few minutes mine did not. Would this be a sign that all is not well?
The other point is that the arm on the pump does not pump the fuel up into the little filter which would be handy as it would save cranking if she is left a couple of weeks and she needs petrol into the carb.
The more gauges you have the more things to worry about. Would the fact the pump arm does not work have any connection with the pump not holding pressure?

The clear filters usually do not run full.

I’m not sure exactly where you have the filter installed.

The clear filters usually do not run full.

I’m not sure exactly where you have the filter installed.

Hi Brian.
I have fitted it as a temporary measure between the fuel pump and the carburettor. I understand that it will not be full of fuel other than if the filter was becoming blocked.
At least it showed me that the lever on the fuel pump was not working.
Are these fuel pumps supposed to hold pressure for a few minutes after shut down or is that for for modern units?
Thanks. Jonathan

Hi Jonathan,
I don’t know about holding pressure.

Where I’ve normally seen the glass filters installed is usually between the tank and pump. The filter inside the tank is upstream of the pump also.

I have no idea if it makes any difference.

Your lever should prime the bowl on the carb. That’s the reason for it.
I know you have to get everything aligned correctly during assembly. Take a look at the diagrams. Maybe something wasn’t put together just right.

Weird I have two posts. I hit submit twice by accident but deleted one. I looked back. It was gone. Now it’s back.

Hi Brian.
Strange things sometimes computers.
I do have a spare rebuilt pump from Greece and the handle on that is much firmer, so when time I may do a swap.
The gaskets on the rebuilt pump looks like a leather type material but when I asked the supplier he said it was not.
In the meantime I am keeping an eye on the clear filter, after two days standing no drop in the amount of fuel in the bowl. I will see after a week at work.
Jonathan