M151A2 has backfire sometimes

[Snoop]

Hi All,


first of all sorry for my bad english, I am from europe...


Since a couple of weeks I have a late model M151 A2
and every day I am learning more and more about that great vehicle.

Today I drove the MUTT and recognized that sometimes,
when I loosen the throttle in gear to shift or to break,
it starts backfiring in the exhaust.
In europe we say "it is in pushing mode" when it starts to backfire

Is this common for the MUTT?


Ciao
Snoop

 

[L1A1]

Today I drove the MUTT and recognized that sometimes,
when I loosen the throttle in gear to shift or to break,
it starts backfiring in the exhaust.
In europe we say "it is in pushing mode" when it starts to backfire

Is this common for the MUTT?


Ciao
Snoop

Snoop
First off, welcome to the site! Secondly no, backfiring is not common to the G838 series of jeeps. Wonder if your fuel mixture is too rich?
Matt

Just found this over on www.g838.org thought it might be of help. http://g838.org/viewtopic.php?f=3&t=1762&p=14195&hilit=mutt+backfires#p14195 So maybe it's your coil starting to go bad?

 

[steelandcanvas]

Welcome! Check your timing.

 

[rickf]

Welcome Snoop, I am one of the ones from that post that was referenced on the 838. Feel free to check them out. One thing you have to check is if you have any exhaust leaks. I would bet that the manifold is leaking where it meets the head and maybe at the junction with the exhaust pipe. If it is set to idle rich then these leaks will cause backfires when you let off the gas as air gets to the hot unburned fuel in the pipe. A bad coil will cut off like someone shutting off the switch while you are driving. Backfiring is a symptom of a bad coil but not the first symptom. The G838.org site has a couple of members in Germany. One from Munich and one from the North but I forget what town.

Rick

 

[Snoop]

Hi again,

thank you for the informations.

I already checked the exhaust system and the manifold for leaks and found nothing.
The carburetor is one of the newer typs with no possibility to adjust CO.

3 days ago I installed new belts and had to remove the air-filter.
Mine has 4 hoses and 1 tube, that I had to disconnect.
Maybe there is a leak now?

What is the right timing point for the late M151 A2?
I have a strobe and adapter wire for plug, but no timing idea...?

Ciao
Snoop

 

[Snoop]

Update:

Just found the timing informations at the decal on the valve-cover.
I flashed the crankshaft pulley with my strobe at idle 500-550 rpm
and the markings were precise in position.

Removed 2 spark-plugs, they were more white than brown - engine runs poor
like all late A2 models.

Also doublechecked all the connections at the air-filter, I removed 3 days ago.
Everything is tight.

Maybe this helps to declare, what I mean with "backfire":

It is not a big "bang-bang" noise,
it´s more or less such a "plop-plop-plop-plop-plop..." while loosen the pedal in gear.

Ciao
Snoop

 

[rickf]

Snoop, All of the carburetors are adjustable for idle mixture. The later model 13660 carburetor has a plug over the idle mixture screw. If you are looking at the engine from the driver side fender the plug is on the carb mounting flange just to the right of the upper mounting bolt. You can drill a small hole just through the the plug and thread in a screw a couple of threads and pull out the plug with a piar of side cutters grabbing the screw. Make sure that when you drill the hole and when you thread in the screw you do not go in very far because the mixture screw head is in there about 10 mm down. Once you get to the adjustment you will be able to adjust as usual for any carburetor. you will find it is turned in too far for emissions reasons. Have you checked the plug wires to make sure they are all good?

Rick

 

[steelandcanvas]

Since it is not a back-fire, and it is a plop, plop, noise could we have a burned valve? Valves out of adjustment? Snoop, have you pulled the valve cover yet?

 

[Snoop]

@ rickf:
THX for the informations about the carb adjustment.
The plug wires are checked. If the problem should be there,
it would also make trouble while accelerating.

@ steelandcanvas:
Also thx to you.
The plop-plop comes out of the exhaust end-pipe.
Maybe like Harley Davidson engines sometimes do.
I can not imagine, that the cause is a bad valve.
But I can lift the valve cover next week.

My german Volkswagen Iltis does this plop-plop in pushing-mode always

Ciao
Snoop

 

[JGBallew]

Most of the A2's I've seen, do this to one extent or another when decellerating. Never seemed to be an issue for longevity.

On accecelleration, that's a lean carb condition, then timing/misfiring, then burned intake valves (in order of potential).

 

[Snoop]

Most of the A2's I've seen, do this to one extent or another when decellerating. Never seemed to be an issue for longevity.

On accecelleration, that's a lean carb condition, then timing/misfiring, then burned intake valves (in order of potential).

Hi JGBallew,

thanks, that sounds good.

Ciao
Snoop