M38 Puffing black exhaust, little power, won't idle well

Jim · Post by **Jim** » Fri Oct 02, 2009 2:31 pm

Whilst out with the missus the other day, our M38 began to
quit while idling. We got it home OK with the throttle. Now it
"puffs" black exhaust and has hardly enough power to go
around the block.
I replaced the fuel filter bubba had put under the frame on
the fuel line. It was full of crud. I then removed the upper part
of the carburetor and ran carb cleaner though every orifice I
could find, and wiped small bits of crud out of the float reservoir.
That hasn't helped. Should I go to the distributor next, starting
with the spark plugs?
It seems to get enough fuel, but doesn't combust it properly.
Removing the gas cap doesn't have any effect.

Jim in Darkest Arkansas

Post by **wesk** » Fri Oct 02, 2009 10:31 pm

Black smoke usually means running rich (Too much gas).

Crud in filter usually means not enough gas so it runs lean.

Your symptoms are contradicting each other.

Is the jeep stock with original fuel system?

Is the roughness and smoke only an at idle thing?

Have you inspected both the accelerator and metwering rod diaphrams for a leaky one?

Have you confirmed the choke butterfly is wide open?

Have you confirmed the heat riser valve is functioning correctly?

oilleaker1 · Post by **oilleaker1** » Sat Oct 03, 2009 8:46 pm

Bad idle after it did run OK, 1st place to look is carburator base gasket leaking due to loose carb. I had to put star washers under the nuts on mine to keep it tight. Everytime it got loose, it wouldn't idle. If that doesn't work, check all your valve clearances. Too tight gives popping in the exhaust at idle or no idle at all cause there is no vacuum if the valves don't go shut. I'm saying all this if it used to idle and run fine before. All that crud you talk about could cause a mess inside the carb. It needs to be clean and funtional. Try for the base being loose and sucking air first!

John

oreo3156 · Post by **oreo3156** » Sun Oct 04, 2009 3:36 pm

how good are the plugs firing?

Jim · Post by **Jim** » Sun Oct 04, 2009 5:30 pm

Appreciate the tips. I've pulled the carb to get it
rebuilt. I ran the Willys first to make sure it was
still doing the same, which it was. I noticed after
removing the carb a pool of fuel in the intake manifold,
which obviously shouldn't have been there. So, off it
goes Monday. Hope this fixes the problem, but if not,
there's still some tips to follow. Thanks, guys!!

Jim in Darkest Arkansas

Jim · Post by **Jim** » Sat Oct 17, 2009 7:00 am

Update: Sent the old carb off to Midwest Military
for an exchange. Excellent return time. Installed
and started it up (took awhile as the new carb
refilled) and she ran. Then I noticed fuel all over
the garage floor.
Bubba or someone at the Kiowa Technical Instute,
for some unknown reason, had cut the fuel line from
the pump to the carb and inserted some type of
flex line from the carb to the cut. It burst.
Shut everything down, mopped up all the fuel
before the War Department got home, and called
John at Midwest. He expressed incredulity at the
flex line, and shipped a correct line out that same
day. It should be here Monday the 19th or so. Still
in time for the National Park's Time Line at Judge
Parker's Courtroom NHS in Fort Smith on the 24th
and 25th. Cautious optimism here.

Jim in Darkest Arkansas

skyjeep50 · Post by **skyjeep50** » Sat Oct 17, 2009 7:45 am

Don't forget to clean out the fuel tank. If that was the source of the crud it can still gum up the new carb. Check to see if the original fuel filter is still in the tank and if it is coated with crud - clean or replace. The original fuel filter is much larger and likely more effective than any of the dinky aftermarket in-line filters. Good luck!

M38 Puffing black exhaust, little power, won't idle well

M38 Puffing black exhaust, little power, won't idle well

Won't idle