Carter YS M38 diagnosis help please

oilleaker1 · Post by **oilleaker1** » Tue Jul 30, 2013 5:18 pm

Well, phase one of the first running and testing of my '51 M38 is complete. Now to fix the small issues. My engine idles fine. The vacuum gage shows a steady 11 inches. No wild erratic movement. I find no vacuum leaks. I never run out of gas, even at full throttle. The problem is that I have to pull the choke out half way to get it to accelerate and run down the road without bucking and snorting. I can push the choke in and it idles fine, but won't pull up off idle very well, stumbles and can die. My thoughts are to go back in and check all the springs, metering rod areas that I just put in with a kit from Midwest Military. Did I get the springs wrong or the incorrect one is my thought. I've read the smaller weaker spring goes on the metering rod side. In the kit were springs different from the ones in it originally. I bought the carb off ebay so who knows if it was correct to begin with. Anybody been here before with these symptoms? Thanks for any pointers for me to check------and I will!

John

Post by **wesk** » Wed Jul 31, 2013 1:02 am

It only takes a few minutes to check the springs. Just pop the diaphragm covers off and make sure the springs are on the cover side side of the diaphragm.

I believe the heavier spring goes in the accelerator pump.

oilleaker1 · Post by **oilleaker1** » Wed Jul 31, 2013 5:49 am

Thanks for the reply. I'll let you know if I get it found and figured out today. I was shocked at how nice it drives. Smoother than my A1. I'm very impressed with the difference between a NDT and a NDCC tire. The NDCC is like a ballon tire when you talk about bicycle tires and ride. John

oilleaker1 · Post by **oilleaker1** » Wed Jul 31, 2013 12:28 pm

Took the two diaphram assemblies off and popped the top off too. All clean and nice, no plugged or dirty passages. Went back to the leftover parts and found the metering rod and accelerator springs much lighter. I put the lighter on the metering rod and slightly heavier on the accelerator side. buttoned it back up and woom. Runs like a kitten. This means to me that the kit springs are wrong!!!!!!!! My advice is to re-use all the jets, springs and rods that are not worn out in your rebuild from now on. John

Post by **wesk** » Wed Jul 31, 2013 12:58 pm

John,

You know what you forgot to do????

Measure the ones that you used!!!!

Here's an example showing what I found in a 950S vs a 637S accelerator pump spring.

oilleaker1 · Post by **oilleaker1** » Wed Jul 31, 2013 5:44 pm

Well, I didn't forget, because i didn't know I needed to. My TM had no directions other than replace it if it didn't work or have the motorpool fix it. The kit had no directions either. Thought of calling John B. next to see if he has a TM for the 637S. Would it be in your sites download section and where? Thanks, John

oilleaker1 · Post by **oilleaker1** » Wed Jul 31, 2013 6:00 pm

OK, found info. in the drivetrain, engine section for the carburator. The new springs in the kit sure look like the pictures in the TM. They do not work in my carburator while the old ones do.

I also used my old metering rod and jet again since they looked fine. In the kit were two different #'d metering rods. Again, no instructions for those. My Jeep now needs the choke to start cold, idles extremely well, no choke once warmed up, just push the floor starter button and it's running. A slight hesitation when pulling off idle and after that pulls fine all the way up to full throttle. No flooding, no back fireing up the carb or in the exhaust. My engine is brand new and needs some miles to break in. The springs are a mystery. John (PS, I'm copying off your excellent diagram and will measure the new springs and compare)

oilleaker1 · Post by **oilleaker1** » Wed Jul 31, 2013 6:10 pm

Did you measure the metering rod springs in a comparison also? Wondering if i got a A1 kit for the M38. John

Post by **wesk** » Wed Jul 31, 2013 8:05 pm

John,

I meant you should have thought kindly enough of the rest of us to measure your old ones, not that it was a required thing.

I've got a comparison photo for the metering spring somewhere.

In this one they look the same but the angle of view differs between them.

The Carb kits sold by Midwest and AJP are all parts necessary to rebuild either a 950 or a 637 but not two. The metering rods that came from Carter have the part numbers on them. If you look closely at the kit you'll see the gasket set has both 950 and 637 gaskets as well.

If you have no part numbers on your metering rods then just use the dimensions I have recorded here.

This is the Midwest & AJP kit.

This is Ron F's kit. This has the correct springs.

Here's the A1's 950S dimensions.

All the above photos are in my albums under M38 &/or M38A1 fuel system.

oilleaker1 · Post by **oilleaker1** » Thu Aug 01, 2013 5:10 am

That is allot of info. to wade through. Reminds me of the instructions booklet that covers all the different models at once when you buy a appliance and are assembling it. All that is left is to throw in 6 foreign languages with it. You forgot to show the correct metering rod jet sizes!

Then there is elevational changes that require different jets and metering rods. Man what a maze. Actually the carburators are very simple to work on and work well with the right parts in them. For now I'm happy mine is working. Thanks for your expertise and photos. John

Post by **wesk** » Thu Aug 01, 2013 7:53 am

You forgot to show the correct metering rod jet sizes!

Actually that is not very important since both are the same part, ORD# 7372519, Carter # 120-157. If you read the spec sheets for the two carbs it is .096 for both.

The springs can be determined by size or PN. They both use the same metering rod spring ORD# 7372534 (Carter # 61-356). For the accelerator pump spring the 637 uses ORD# 7372535 (Carter # 61-304) and the 950 uses ORD# 8329834 (Carter # 61-460)

The ORD 9 parts lists solve any questions on which parts are different between the two. It just takes a little patience, time, research of the readily available documents and some measuring skills to use the Midwest/AJP kits.

artificer · Post by **artificer** » Fri Aug 02, 2013 12:32 pm

oilleaker1 wrote:My engine idles fine. The vacuum gauge shows a steady 11 inches. No wild erratic movement. I find no vacuum leaks.

That is a very low vacuum reading & all being correct should be in the 17-21 range. Check the intake manifold for security plus look @ scenario number 10 http://www.secondchancegarage.com/public/186.cfm

oilleaker1 · Post by **oilleaker1** » Fri Aug 02, 2013 4:49 pm

I think my old cheap vacuum gauge is off, but I was wondering if it was erratic or steady. Was looking for a leak that way. I attached it to where the rubber hose takes off to the wiper system, and it has to go throught the vacuum side of the fuel pump to get back up the the intake manifold port. Thanks, John

artificer · Post by **artificer** » Fri Aug 02, 2013 6:24 pm

You need manifold vacuum not vacuum pump.

Carter YS M38 diagnosis help please

Carter YS M38 diagnosis help please

Re: Carter YS M38 diagnosis help please