YS 637s rebuild kits

davem201m38 · Post by **davem201m38** » Tue Jul 14, 2020 4:32 am

Hi all,
I've been on the usual dealer web sites and I'm struggling to find an Ethanol proof rebuild kit for the M38 YS carb from a Military dealer, I just don't see one in the lists.
I have found one from a Carb parts dealer but I'd prefer to fgo with somebody known.

I'm in the UK so it will need to come from the US.

Ta, Dave.

G740 · Post by **G740** » Tue Jul 14, 2020 5:06 am

Midwest Military has a good kit. Nothing is "proof", but resistant is the operative word. The kit is made from current material used with today's fuels.
John

davem201m38 · Post by **davem201m38** » Tue Jul 14, 2020 7:42 am

I couldn’t find it on The site, where? I didn’t see it under fuel.

davem201m38 · Post by **davem201m38** » Wed Jul 15, 2020 4:32 am

Ah, found it, no picture, I see.

G740 · Post by **G740** » Wed Jul 15, 2020 5:38 am

Full overhaul kit. Everything needed to rebuild your housings.

davem201m38 · Post by **davem201m38** » Wed Jul 15, 2020 6:04 am

OK folks. I have 2 x 637s to rebuild. And have ordered the kits up from a Midwest.
Apart from the hic up of the spring being shown in the wrong position On Fig 60 of chapter 9 of the manual is there anything else I need to be aware of? Wes?...
Thank you,
Dave.

Post by **wesk** » Wed Jul 15, 2020 11:33 am

Mainly use the full panel of technical manuals available to you.

Disassembly should always be done on a clean work bench with good tracking (photographs etc) of the process and good inventory of parts. Tiny check balls have a tendency to vanish!

davem201m38 · Post by **davem201m38** » Wed Jul 15, 2020 1:23 pm

Yes thanks Wes, I’ve got the manual and I remember from years ago your warning about that spring, I bought Midwest kits assuming quality, if they turn out to be the same as the kits I can get over here I’ll kick myself.
Cheers, Dave.

Post by **wesk** » Wed Jul 15, 2020 1:57 pm

Remember I said:

Mainly use the full panel of technical manuals available to you.

For the M38 that would be TM 9-1826A, TM 9-8012, TM 9-804, TM 9-1804A, ORD 9 SNL G-740 and Carter YS637S Spec sheet.

John at Midwest and AJP sell the same kit as I recall. It is a covers both kit since it has the items for both the YS637S and the YS950S. Be carefull which parts you use. Also the thick manifold insulating gasket with built in diverter is not in that kit.

Be sure to take advantage of my M38 fuel system photo album:
http://www.willysmjeeps.com/v2/modules. ... _album.php

Midwest & AJP Kit.

Ron Fitzpatrick's kit.

This is the correct carb to manifold gasket for the M38.

Carter spec sheet pg 1

Carter spec sheet pg 2

davem201m38 · Post by **davem201m38** » Wed Jul 15, 2020 2:06 pm

Thank you Wes. John doesn’t actually show a picture on his website so I missed it at first. We’ll see how this goes.

Post by **wesk** » Wed Jul 15, 2020 3:12 pm

The photo I posted was of one of his kits I used in 2006.

This is AJP's ad for their kit which is the exact same kit used by Midwest.

davem201m38 · Post by **davem201m38** » Sat Jul 18, 2020 1:43 pm

OK, used Seal Tested kits from Midwest Miltary, seem good kits with everything you could need plus more, arrived in 2 days to the UK, excellent.
But 2 things, now I've rebuilt the first carb.

Nice thing is the springs are bagged with the diaphrams so there's less chance of getting them mixed up.

1. Does anybody know why the kit that seems 637s specific has 2 metering rods? Nothing to say that they are different in the packaging and the numbers on them are too faint to read.

2. The kit comes with a Bleed Tupe Inner as well as the Bleed Tube assembly.
No way could I figure out how to get the inner bleed tube out of the carb body so I left it. Removing it isn't metioned in the TM. So how does one extract the Bleed Tube?

Ta, Dave.

4x4M38 · Post by **4x4M38** » Sat Jul 18, 2020 8:29 pm

Then and Now also sells rebuild kits, fyi.

davem201m38 · Post by **davem201m38** » Tue Jul 21, 2020 2:10 am

Hi Wes,
OK I've now rebuilt one of the carbs, pretty easy just follow the manual, mine was missing pages some so read the dismantling instrucions in reverse.

How ever there is a problem with Seal Tested kits, the kit seems excellent with the parts in it, more than you will need BUT....

In one kit, the first I opened there are 2 metering rods, though the pack says it's for 637s (the kit mentions no other carb) it also does the 950. The metering rods are very poorly etched / marked and the numbers are unreadable and both metering rods look identicle. The vendor told me that the 637s metering rod has slightly rounded corners. These are darn hard to see with the naked eye.

Looking in the second rebuild kit, one of the metering rods is unreadable, and luckily one can be read, 75-826S does seem to have slightly square shoulders so the unreadable metering rod is the one to use for the M38 carb.

I imaging if out of 2 complete kits there are 3 metering rods that have unreadable numbers other folks might have the same problems occasionally,
Cheers, Dave.

Post by **wesk** » Tue Jul 21, 2020 9:57 pm

The AJP & Midwest Mil kits are for both the 637S & the 950S so they use different metering rods. As I said earlier, take advantage of my M38 and M38A1 fuel system sub albums they have illustrations of the two metering rods with measurements.

The inner bleed tube is not threaded and it is not a press fit. It is a light interference fit and is easily removed by gripping gently wit a pliers and twist back and forth as you pull it out. You insert it by hand and the threaded outer tub retains it.