willysmjeeps.com

'54 M38A1 just about all stock with stock carb. The motor runs just fine, seems to have plenty of power (for an F-head) and really don't have any complaints. Here's some specifics:

-54 A1
-stock carb/air cleaner/ etc
-12 volt system
-rebuilt carb 18 months ago with Midwest Mil kit
-have about 1000 miles on the rebuild
-motor runs well on and off road
-plugs show normal color, porcelain is mostly white and electrodes -brown/gray.
-tailpipe is sort of black, which led me to wonder if it was running a tad rich
-but the float level is right on where I set it during the rebuild (1/4")

Because of the look of the tailpipe, I wondered if it was running a tad rich. I pulled the top of the carb off and all looks good except that the fuel level in the bowl was low. The jeep hadn't run in 3 days.

If I have not used the jeep in, say, a week, it takes a bit of cranking to get it going. Considering the jeep starts up almost immediately if it is used regularly, I suspect that the fuel in the bowl is leaking out.

I took a flashlight and looked down the carb to the intake manifold and it is damp down there- it's obviously fuel. There is no fuel leaking outside the carb.

So, my suspicion is it's got a problem with fuel draining out of the carb into the intake. So long as the jeep is used regularly, and especially if used at higher speeds, it seems fine. But if not used for awhile, it definitely takes longer to fire up.

I have the manual for the YS 637 (M38) and the only thing it says if fuel is leaking out is to tighten the bowl plug. I'll eventually take it back apart, I suppose, but thought I'd first ask here to see if anybody else has had this problem.

Check the entire bowel interior surface closely for fine cracks in areas that would be covered with gas.

Evaporation is a common enemy of storage or prolonged parking of the jeep. That is why the military fuel pump came with a manual pump handle on it so you can hand pump the bowel full before you attempt a start.

Wes, what would be your expectation for evaporation out of the bowl? How long for it to drop halfway down, for example?

I live in a pretty cool and damp climate- it's not like the jeep sits cooking in the sun. In fact, that gets me thinking that might explain the tailpipe looking a bit blacker than I'd like- namely that the jeep gets to operating temp no problem, but I never drive more than about 10 miles in any direction (consequence of living on an island). Maybe it just never gets the chance to get that soot out of there.

I'll take another look at the bowl for any fine cracks, but I did not notice anything like that the first time I took the carb top off to re-check the float.

If no cracks I would say the wee bit of fuel stain in the manifold would be from the last run and the shortage of gas in the bowl to evaporation if jeep is sitting for a week or more. This would have been the average sitting time for spare jeeps in the military and was probably why the Army wanted the hand operated pump handle on the fuel pumps.

Short runs like yours usually result in a bit of soot in the tail pipe and an inordinate amount of moisture in the oil.

Thanks for taking the time on this, Wes. It's a big help in trying to understand what it is I'm seeing with the jeep.

The jeep runs well, but I'll monitor it all the same.

Something I neglected to ask on the prior post: is it inherent in the waterproof YS series carbs that they tend to allow evaporation of the fuel in the bowl at greater rates than you'd see with a more conventional carb?

Also, my fuel pump is stock and has the handle; is it recommended to use it or just rely on the starting procedure to fill a (partially) drained bowl?

I usually suspect dirty or damaged check valves in the fuel pump might be causing fuel to drain back down from the carburetor. If the jeep sits for a while and you don't manually prime the system then it takes quite a bit of cranking to get a good supply of fuel back up to the carburetor. ... Brian