Carb rebuild info

Kaiser59 · Post by **Kaiser59** » Thu Sep 28, 2017 7:15 pm

I have a YS 950s carb on a 1953 M38A1 jeep and am having trouble locating a carb kit in Canada for it. I can get my hands on a kit for a YS637S but I do not think or know if this kit is compatible or not. Also I need to know if the metering rod pin is supplied within the kit whereas the one for my carb is missing. any or all info to this query would be greatly appreciated thank you.

4x4M38 · Post by **4x4M38** » Thu Sep 28, 2017 8:12 pm

Great Jeep name!

Start here:
http://www.willysmjeeps.com/v2/modules. ... de=results

Scoutpilot here also rebuilds carbs and fuel pumps
for a fee.

Take care,

Post by **wesk** » Thu Sep 28, 2017 9:31 pm

The two carbs are very different yet the most popular carb kit out there services either one leaving a few left over parts. John at Midwest Military here in Minnesota and George at Army Jeep parts in Pennsylvania and Ron Fitzpatrick Jeep parts in Oregon all offer the kits.

You will find a lot of help in my technical photo album:
http://www.willysmjeeps.com/v2/modules. ... _album.php

The AJP or MWM kit.

Currently Fitzpatrick G503 is out of stock on the M38A1 YS950S Kit.

Kaiser59 · Post by **Kaiser59** » Fri Sep 29, 2017 7:56 am

Thank you very much wesk for your prompt response and most valuable info in regards to my problem. With this detailed info I am assured that i can refurbish this carb properly to its original performance capability. I have acquired this task through an ex brigadier general of whom I now feel confident that I will be able to complete this without a problem for your info has helped shorten a quest we were having trouble to resolve. Again many thanks and take care.

Post by **wesk** » Fri Sep 29, 2017 10:48 am

One more small issue you will run into. Tech publications. There is no civilian equivalent for that YS950S carb. Therefore the only pub available for it's overhaul is the US Army TM 9-1826A dated 1952. Due to it's publication date it only contains instructions and specifications for the YS637S. It's parts illustration on page 114 has a very important error. It places the metering rod spring on the incorrect side of the diaphragm. We have a corrected illustration but I recommend that folks with the YS950S use a copy of the ORD 9 or Canadian parts manual for reference during overhaul. I also located an original Carter Carb specifications sheet for the YS950S so folks now have sufficient data to properly overhaul the YS950S.

These manuals and manual excerpts are found on our"Downloads" page:
http://www.willysmjeeps.com/v2/modules. ... =Downloads

This is the specific link for the TM 9-1826A exerpts and spec sheets:
http://www.willysmjeeps.com/v2/modules. ... it&lid=165

This is the YS950S spec sheet.

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.

This is the corrected illustration in TM 9-1826A. I have moved the item BB to it's correct position.

This is the YS950S illustration from the M38A1 ORD 9 parts manual.

Kaiser59 · Post by **Kaiser59** » Fri Sep 29, 2017 10:58 am

Good day Sir and thank you for the update material. Approximately 20 mins ago after i spoke with the gentleman that owns the jeep thanks to your info he spoke with a colleague of his and low and behold acquired the proper carb kit from him that you had specified to do the job correctly your help is this matter is very much appreciated.