Help! with m38a1 carb?

[tjmilitary]

OK guys I need help trying to figure out whats going on with my jeep. It just started running rough and too rich. So I rebuilt the carb and no change. It seems like when it sits and idles its ok for a while then loads up bad. On the other hand when you take it for a ride I seems like it is starving for fuel. Has no power, wil sipt and sputter and sometimes even die. I need some help to figure it out.

 

[dougimes]

Bowl level can cause what you are seeing. Start by checking fuel pressure at carb inlet, then look at the float action.

 

[tjmilitary]

Thats what I was thinking. I could not find anything about how to adjust the float. How do I go about doing that and also how do I check the fuel pressure?

 

[ARDUECE]

i just sent one to american carb in florida. for 125 they make it new. they bebulid,rebush the throttle shafts, replate it, flow test it and gaurentee for a year. 145 they gaurentee it for life. check your floats and pressure like dougimes said. also check to see if your throttle shaft has alot of wear.

 

[tjmilitary]

THe throttle shaft does not have very much wear and I just replaced the seal. Can someone tell me how to properly adjust the float and check the fuel pressure and what pressure should it be set at?

 

[idiocrates]

I'm guessing you have the original YS carb....if not....this does not apply. With the airhorn removed from the body of the carb.....invert the air horn and hold it level so that only the weight of float is on the needle. The distance from the lowest point on the seam of the float to the machined surface of the bowl cover should be one-quarter (1/4") inch. If you do not have level gage CAR-T109-81 I have founf that a 1/4" drill bit will work equally well. Simply lay the drill bit on the machine surface of the air horn and slowly roll it under the float. If the float is lifted at any time or if the float clears the bit excessively you will need to adjust the needle acuating tab accordingly. Always adjust the level by bending the lip of the float. Do not bend the float itself. Also, this procedure is done without the fuel bowl to air horn gasket in-palce.
As to the desired input fuel pressure.....the book says the fuel pump should be able to supply 4 1/2 to 5 psi at 1800 rpm. Hope this helps.

Jim

 

[tjmilitary]

Thanks Jim

I will try that tomorrow. Rebuilt the pump today. Held the lever in to tightin the screws like everyone says. It did not work. I guess I will take it off again and try it without holding the rod in.

 

[modified]

I'm guessing you have the original YS carb....if not....this does not apply. With the airhorn removed from the body of the carb.....invert the air horn and hold it level so that only the weight of float is on the needle. The distance from the lowest point on the seam of the float to the machined surface of the bowl cover should be one-quarter (1/4") inch. If you do not have level gage CAR-T109-81 I have founf that a 1/4" drill bit will work equally well. Simply lay the drill bit on the machine surface of the air horn and slowly roll it under the float. If the float is lifted at any time or if the float clears the bit excessively you will need to adjust the needle acuating tab accordingly. Always adjust the level by bending the lip of the float. Do not bend the float itself. Also, this procedure is done without the fuel bowl to air horn gasket in-palce.
As to the desired input fuel pressure.....the book says the fuel pump should be able to supply 4 1/2 to 5 psi at 1800 rpm. Hope this helps.

Jim

If I may correct you Jim, the TM's state; 9/64" clearance of float ..also, I'd check for vacuum leaks and loose connection along your fuel line from tank to carb. If you need further help .. I suggest you join willysmjeeps.com ....the site also provides the manuals needed to troubleshoot and proper maintenance procedures as required.

 

[idiocrates]

hmmmm.......well......my info comes from the TM9-1826 manual (although I have no date on the document)....Chapter 9, Section 95 - Data, Pg. 112, Table VIII shows.....Float Level (in)........1/4. And again in Section 102 - Float Level Adjustment, Pg. 118, Ref. Fig 61......one-quarter inch. Either we're talking two different carbs......or we're within 1/64 of an inch from agreeing.

 

[jhooah]

Just replaced the Accelerator Pump pistion (Rubber) in my WWII GPW, then found the one in my 3/4t Dodge Zeinth was frozen inside the well (Bronze).
Been away in Afghanistan for a year, no one drove them and seems the new crappy 10% fuel messed up the innards.
Might check the accelerator piston to see if it's frozen or destroyed. Engine wll start, idle, but upon acceleration cough sputter and act like there's no fuel.
V/R W. Winget
www.VMPA.us

 

[modified]

hmmmm.......well......my info comes from the TM9-1826 manual (although I have no date on the document)....Chapter 9, Section 95 - Data, Pg. 112, Table VIII shows.....Float Level (in)........1/4. And again in Section 102 - Float Level Adjustment, Pg. 118, Ref. Fig 61......one-quarter inch.

Either we're talking two different carbs......or we're within 1/64 of an inch from agreeing.

Jim, you are correct as to what tm9-1826 states, but the army never updated the manual for the M38A1. the manual was originally written for the M-38's YS-637 S.(Very similar in design and outer appearance, yet different body casting entirely) This manual carried over with scarce detail amendments that outlined the M38A1's YS 950 for provided larger metering rod, larger diam throttle port , and decreased float clearance towards the higher fuel capacity in the carb for the larger (albeit, not that much) displaced Hurricane F-134. motor found on M38A1.

Either we're talking two different carbs......or we're within 1/64 of an inch from agreeing.

...Yes we are talking about two diff carbs. and no, 9/64" is far from "1/64 of an inch from agreeing........were almost at half(.125 or 1/8" ) the argued distance!!!!!
read below as I had borrowed this info from WesK on the "G503":



by Cuz » Mon May 19, 2008 3:58 pm

Although the YS950S is not specifically covered in the TM 9-1826A the overhaul procedures listed there for the YS637S can be used together with the spec sheet below to complete a proper overhaul. If you don't have this manual I have the data posted on our M38.M38A1, M606, CJV35 specific web sites. You are welcome to visit them and join.
Willys M Jeeps
M38-M38A1-M606 : Willys/Kaiser M Series 1/4 Ton Jeeps

Carter YS950S 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
over, 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 (.021inch) 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 valv

Vacuum Spark Port: --------------------------------------------------------- None.


Specifications copied from a one page bulletin from Carter Carburetor Form 4960B released March 1953, revised March 1956.

 

[idiocrates]

well, jeeeeeez.......no wonder I can never get my checkbook to balance.....you are correct, sir.....and thanks for the great info. So is it still correct to say that the only real adjust ment on the carb during an overhaul is the float level? I mean, all those other numbers listed are derived from machined needles and seats and preformed bodies.....right? Just curious.....cause I will surely forget the answer once I've had a chance to take a short nap.......zzzzzz

 

[Maverick1701]

well, jeeeeeez.......no wonder I can never get my checkbook to balance.....you are correct, sir.....and thanks for the great info. So is it still correct to say that the only real adjust ment on the carb during an overhaul is the float level? I mean, all those other numbers listed are derived from machined needles and seats and preformed bodies.....right? Just curious.....cause I will surely forget the answer once I've had a chance to take a short nap.......zzzzzz

This video has great how-to about 950ys carb float adjustment. 9/64s