M38a1 keeps fouling plugs?

oreo3156 · Post by **oreo3156** » Sat Aug 22, 2009 5:55 pm

I'm running 12 v with standard plugs. Jeep runs great for about an hour, but then fouls a plug. Replace with 4 new ones, then seems to run great. Timing is dead on. Doesnt seem to be running super rich or anything. Any thoughts?

Post by **wesk** » Sat Aug 22, 2009 10:11 pm

What is fouling your plugs? Oil, gas, metal? You need to inspect them closely as soon as they fail. The fouling agent will lead you to the cause.

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 8:07 am

really dark, quite black. Jeep doesn't smoke. I'm thinking fuel, its running too rich. I've set the float height and its perfect. How can I lean it out a bit?

linx310 · Post by **linx310** » Sun Aug 23, 2009 8:22 am

really dark, quite black. Jeep doesn't smoke. I'm thinking fuel, its running too rich. I've set the float height and its perfect. How can I lean it out a bit?

Could you have a vacuum leak of some sort throwing off the mixture? I think that would make it run to lean though....

Post by **wesk** » Sun Aug 23, 2009 8:37 am

Too Rich means too little air or too much gas. If you are running the stock YS950S carb and Carter dual action fuel pump then here are a few possibilities.

Too much gas:
1-Float too high.
2-Float needle not seating correctly.
3-Metering rod wrong one.
4-Metering rod diaphram leaking.
5-Metering rod and accelerator pump springs reversed.
6-Accelerator pump diaphram leaking.
7-Fuel pump pressure too high. (this can cause #2)

Too little air:
1-Choke plate not full open.
2-Air cleaner oil level too high.
3-Restriction in induction path.

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 11:23 am

I'll take it apart and post a few pics, see if I'm missing anything

Post by **wesk** » Sun Aug 23, 2009 12:18 pm

D the easy itmes first IE Too Little Air

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 12:59 pm

Was just out messing around with it, now its not getting any fuel and won't start, plugs super dry. Fuel gets to carb, and float is not stuck. Lots in the bowl.

any ideas?

also, the check ball drops down in first, then the weight, correct?

Post by **wesk** » Sun Aug 23, 2009 1:17 pm

Get a little squirt oil can. Fill it with gas. Disconnect the air in hose from the carb. Make sure the choke is wide open. squirt an ounce of gas in there and start it. If it fires and runs then you hav trash in the metering port/tube or the rod is stuck. You have confrimed you have spark and compression?

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 1:22 pm

wesk wrote:Get a little squirt oil can. Fill it with gas. Disconnect the air in hose from the carb. Make sure the choke is wide open. squirt an ounce of gas in there and start it. If it fires and runs then you hav trash in the metering port/tube or the rod is stuck. You have confrimed you have spark and compression?

yes, 120 lbs and fire is great.

Got the carb all apart, everything look in order. Ordered a rebuild kit for good measure, but gonna try it again.

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 3:21 pm

got it running but idles rough and runs super rich when idling. (Black smoke) Once its reved up it works awsome.

Are the two springs on the two diaphrams supposed to be the same?

After you let it sit and cool down, it doesnt like to start again unless you hold it to the floor.

Post by **wesk** » Sun Aug 23, 2009 3:42 pm

You probably shouldn't do the carb "Monkey do Monkey see" since theres several ways to get the parts in there wrong. Mixing up the two diaphram springs is the biggest BooBoo followed by getting them on the wrong side of the diaphrams.

Use the Carb overhaul manual sections here:

http://www.willysmjeeps.com/v2/modules. ... tit&lid=71

But be sure to note on page 3 spring “BB” is shown in the wrong location. It belongs between the cover FF and the diaphragm DD.

Use this 1952 manual exerpts that cover the YS series but was published before the YS950S came out. Just use the YS950S spec sheet with this manual.

Carter YS Carbureter No. 950S

CARBURETER SPECIFICATIONS
For Willys 4 Cylinder Engine: 3 1/8 Inch Bore, 4 3/8 Inch Stroke
Dimensions:
Flange size, 1 1/4 inch S. A. E.
Primary venturi, 11/32 inch I. D.
Secondary venturi, 19/32 inch I. D.
Main venturi, 1 1/4 inch I. D.

Float Setting: Distance from seam of float to float chamber
cover, with weight of float on needle and spring: 9/64 inch.

Vents:
Balanced thru air horn to air cleaner via tubing external to carbureter.
Vent: Bowl chamber to carbureter bore, size No. 68 (.031 inch) drill.

Gasoline Intake:
Square vertical (spring loaded) needle No. 53 (.0595 inch) drill size in needle seat.
Bleeder tube, assembled over idle tube, with 2 side holes--No. 65 (.035 inch) drill.

Low Speed Jet Tube:
Jet size, No. 70 (.028 inch) drill (in end of tube).
Auxiliary jet (on side of tube) size: No. 75 (.021 inch) drill.
By-pass (in air horn) size: No. 52 (.0635 inch) drill.
Economizer (in body) size: No. 54 (.055 inch) drill.

Idle Port: Upper port: slot type, length, .165 inch. Width,
.030 inch.

Idle Port Opening: Top of port--.125 to .129 inch above top
edge of valve with valve tightly closed.

Lower Port (For Idle Adjustment Screw): Size, .053 to .057
inch diameter.

Set Idle Adjustment Screw: 1/2 to 1 1/2 turns open. For richer
mixture, turn screw out. Idle engine at 700 R.P.M. with deep
fording vents open.

Main Nozzle:
In primary venturi, angle 20°.
Discharge jet size, .0935 inch inside diameter.
Main nozzle bleed (tube in air horn) Size: No. 70 drill.
Metering Rod (Diaphragm operated):
Economy step, .070 inch.
Power Step .054 inch diameter.
Vacuum passage restriction, size: No. 50 (.070 inch) drill
Vacuum passage bleed to bore, size: No. 65 (.035 inch) drill.

Metering Rod Jet: Size: .096 inch diameter.

Accelerating Pump:
Diaphragm type, vacuum operated.
Discharge jet size, No. 72 drill.
Intake ball check size: No. 40 drill.
Discharge ball check under needle, size No. 50 drill.
Vacuum passage restriction, in flange size: No. 52 (.0635 inch) drill.
Vacuum passage air bleed to bore, size: No. 62 (.038 inch) drill.

Pump Stroke: No adjustment.

Choke: Manual--Offset, butterfly type with poppet valve.

Vacuum Spark Port: None.

Specifications come from a one page bulletin from Carter Carburetor Form 4960B released March 1953, revised March 1956. I have tried to keep the layout of the form. However, it should be in two columns.

Also be sure to use the new production $55 carb kit from MWM and AJP. This is a complete kit that covers both carbs and comes with modern rubber parts that are compatable with todays gas. Also be carefull with parts that look similar but are for one or the other carb.

oreo3156 · Post by **oreo3156** » Sun Aug 23, 2009 4:56 pm

ordered one from MWM Does it come with instructions?

I wonder if the guy that had it before me screwed it up, I'd say yes because the two housing covers are the same and so are the springs. I'd say I just found the problem......

Post by **wesk** » Sun Aug 23, 2009 6:03 pm

No the kit does not come with instructions nor does it come with a parts illustration.