willysmjeeps.com

hello folks,my m38a1 have a idle problem,
when engine run at idle speed,the sound is very nice one moment and a second after it became like miss firing and after few second against normal,(something like up and down),
my jeep is fully done with proper stuff ,couple mounts ago I've change a new carburetor not rebuild but original ,and since a couple of days ago was wonderful riding,.
this make me crazy,today I've change the condenser and gap,check an clean carburetor but all is fine,and nice blu spark ,noting happen same idle, up and down..
I've notice when engine stall down popping and black smoke come out from the exaust pipe,...sad...
please help me

You said this started after replacing the carb so we can assume the problem is the carb and not ignition.

A variation in idle can be caused by several items.

1-Carb throttle shaft has excessive clearance at bushings.

2-Dirt in fuel causing flow issues at float needle.

3-Choke plate loose and closing part way off and on.

4-Intermittent blocking of the lo speed circuit passageways.

Download and review the manual sections for the carb at:
http://www.willysmjeeps.com/v2/modules. ... tit&lid=71

no sorry Wes ,I run the jeep with this carburetor for a couple of mount,
and carb,950s it's a new unit,no rebuild,brand new,so I assume all the specification are correct,like spring length,jets etc

I was follow the motor tune up specification came with the carburetor box as form 4960B,
-spark plug gap,breaker point and idle adgjustment,done,only remain to check the float setting,

I was thinking about the diagram from accelerating pump,so ten minutes ago I've remove and check,the diagram was a bit wet so I decide to replace with another one,put back in position an try to start, same problem,up and down,.,.
mhh ...
thanks for helping me
regards
Gian

If this carb was a NOS unit. (new in box but manufactured many years ago) I would check all rubber parts. 10 to 12 years is a maximum shelf life for the rubber parts.

Was the carb interior flooded with a preservative oil as it should have been? If dry this preservative oil may have dried and is now breaking down to particals that are intermittently plugging up passageways, jets and valves.

No carburetor was not covered by preservative oil,just dried stuff ,

I don't understand why i drove 2 months without any problems,and all of a sudden this problem happened

do you think I have to blow the passage in carb

I try to describe the prob in different ways,
jeep run at minimum rpm,after 10 seconds rpm goes down and popping from exaust,after that it's comes up at normal rpm
when popping I've notice black smoke come out from exaust

likely just took this long for the solvent action of the fuel to break down whatever was on it.

Like a rubber old style black diagram,I have ready replace but noting change,tomorrow I will try to put a new set of spark.,.
this problem make me crazy,but I like It because I love my jeep..

I had something similar happen.... the center wire on the distributor (from coil) was not shoved in all the way with the result that one minute is was fine, the next it ran rough, backfiring and the like. I had unintentionally disturbed the wire when doing other things to the engine.

I spread the contact area of the wire a little to give it a better grip and pushed it all the way in and the problem went away.

Otherwise, it's probably what the other guys have suggested.

Tim

That deteriorated black rubber diaphragm that you replaced most likely already sent many small particles throughout the carb's passageways.

As I have already posted if the jeep ran fine before you swapped in the new carb don't waste your money on ignition parts and spark plugs.

If it's proof you want remove the new carb and put the old back on.

Problem goes away then you will know there's no reason to play with parts replacements in all the other systems!

The run up at high RPM, hold for a while, and then the crapping out sounds like a fuel problem. Have you checked for contaminants in the tank itself ie:water? The backfire at high RPM could indicate this.

The black smoke tends to indicate rich mixture. Water would result in lean mixture.

Ok,Ok guys I found the problem,
it was a loosen bolt holding a carburetor to the intake manifold,.
in some cases the problem is very stupid ,and I have learn to love more my A1......(no comment please)
I'm very happy,and my boys to and tonight I can show a big smile to my wife....
thanks a lot everybody