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I've recently rebuilt the carburetor on my M38A1, and I have a question about the one-way valve that replaced the vent line that ran to the transfer case, after vehicle No. 23359. I have assumed that this vent would be one way into the vacuum pump -- in other words, it would allow air to be sucked into the pump, and not allow air to be pushed out.

However, as an experiment, I blew in and out of the original valve that came off my carb before the rebuild, and I've found that I can blow air out of it, but cannot suck air into it (don't worry - I cleaned it up before doing so, mostly).

That seems backwards to me. I have assumed that the original set up before vehicle 23359 would have created negative pressure in the line that led to the transfer case. Am I missing something?

Thanks all, and Happy Friday!

I assume you are referencing the valve on the fuel pump. It flows outward away from the pump on early M38A1's. This allowed the fording system when closed for fording to pressurize the transfer/tranny thru that valve as the engine crankcase pressure rose. The late M38A1 uses a simple vent with shield that also flows away from the pump. I am not sure why you were attending to this valve while rebuilding your carb?

Thanks Wes! That answers my question - and clearly I was having a "senior moment" -- I meant fuel pump, and for some reason typed carb.