Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Thu Nov 22, 2012 5:44 pm Post subject: YS950 S carb question
OK - I got my hands on a nice Carter YS carb. It had been rebuilt by the fellow who sold it to me but never run.
I installed it according to the manual, including running the vent line to the port on the crossover tube. The fuel / vacuum pump is the military type, recently rebuilt, installed with the correct spacer and plumbed with the pressure port connected to the fitting on the manifold below the carb thru a Tee attached to the PCV as shown in the manual. The vacuum port is only connected to the wipers inasmuch as I don't have the military distributor.
The engine a F head "Hurricane", however it is from a 1962 CJ5 not a M38A1. It runs great with a Carter YF.
Anyway, I installed the YS, started the engine and it appeared to run OK. I took it down the road for about 2 miles at 25-30 and it ran smooth. Giving it the gas I accelerated to about 50 and it started bucking, backfiring once. By letting up on the throttle I managed to get it home where it stalled when I took my foot off the gas. It would not restart.
Investigation showed: 1.) Fuel in the bowl 2.) plenty of fuel pressure 3.) Spark 4.) Black and wet plugs that had to be cleaned before they would fire. Cleaning the plugs and reinstalling the YF Carb and the Jeep ran normally.
Anybody have any suggestions for me?
Happy Thanksgiving!
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
Certainly sounds like it was running too rich. Since we know it runs fine with the YF both before and after that pretty much tell us the problem is in the YS.
What can make the YS too rich?
1 - Just how experienced was the rebuilder?
2 - Are the correct springs on the two diaphragms in the correct side and the correct place?
3 - Are the diaphragm rubbers late type ethanol resistant?
4 - Is the metering rod the correct Part #? (75-826S)
5 - Was the bowl full or overfilled?
6 - Was the float needle and seat sealing or not?
7 - Are there any cracks in the bowl?
There are only two connections on the carb for plumbing. The bowl vent to the crossover tube and the fuel pump pressure line to the bowl inlet fitting. So I am curious what "Pressure line" you connected to the intake port below the carb? Or are you referring to the manifold vacuum line that goes to the PCV valve plumbing at the lower left side of the block? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Fri Nov 23, 2012 11:58 am Post subject: YS950S
Wes,
You always nail me on the terminology, especially when we are talking about the fuel / vacuum pump. The other line I referred to is the manifold vacuum line that goes to the PCV valve, etc.
I'm not at home but I can answer a few questions.
1.) the rebuilder has a lot of experience rebuilding carbs. He goes thru them and then resells them.
2.) how would I know if the springs were correct? Are they different lengths?
3.) I asked this question and he said they were of recent manufacture so he assumed they were. I can't verify that at this time.
4.) will ask PN of rod
5.) when I removed the top of the carb while still on the engine, the bowl was not overfilled.... At least I didn't have gas running all over.
6.) the million dollar question.
7.) none that I can see.
Whatever it was doing quickly fouled out the plugs. I was not nearly so quick to realize that fouled plugs may have been why I couldn't restart it. I'm tempted to check what I can and put it back on for another try. Just maybe something was interfering with the float valve sealing. It was very clean inside with no visible debris so I'm at a loss to explain why the float wouldn't seal unless being bounced around in shipping caused something to hang up.
From what you've said, I take it there is no reason the carb shouldn't work on a civvy F head with the crossover and etc. installed. You can tell by this question that I'm a real mechanical whiz.
Thanks for giving me some ideas...
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
1-Perhaps I should have asked: How many YS series Carter carbs has the fellow rebuilt?
2-The ORD 9 shows the difference in size and which goes where. The TM 9-1826A in our downloads section also offers some of this info. Be sure to use the corrected drawing. My photo album has dozen of detailed photos: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album115&op=modload&name=gallery&file=index&include=view_album.php&page=1
3-You can simply remove the two diaphragm covers and if the diaphragms are deteriorating and leaking (wet on both sides) then they are not late enough. An experienced YS rebuilder will know which kits are current production diaphragms.
4-Pull the rod yourself and check the number. Just 4 screws and slide it out.
5-To ascertain weather the bowl is overfilling or not you will need to apply 3 or 4 pounds of pressure fuel flow to the float valve while observing the bowl upper area for overflow.
6-See 5.
7-Warm the carb body up with a heat gun then inspect for cracks.
Either carb will function just fine on either engine. The differences one needs to be aware of are the operation and adjustment of the accelerator pump systems and the correct application of the choke during starting. The YS carb with the vacuum operated accelerator pump must be started with the choke fully applied. This ensures adequate venturi vacuum to operate the diaphragm. Pumping the pedal on the YS carb does not help in squirting gas in to help with starting. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
1-Perhaps I should have asked: How many YS series Carter carbs has the fellow rebuilt?
2-The ORD 9 shows the difference in size and which goes where. The TM 9-1826A in our downloads section also offers some of this info. Be sure to use the corrected drawing. My photo album has dozen of detailed photos: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album115&op=modload&name=gallery&file=index&include=view_album.php&page=1
3-You can simply remove the two diaphragm covers and if the diaphragms are deteriorating and leaking (wet on both sides) then they are not late enough. An experienced YS rebuilder will know which kits are current production diaphragms.
4-Pull the rod yourself and check the number. Just 4 screws and slide it out.
5-To ascertain weather the bowl is overfilling or not you will need to apply 3 or 4 pounds of pressure fuel flow to the float valve while observing the bowl upper area for overflow.
6-See 5.
7-Warm the carb body up with a heat gun then inspect for cracks. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Sun Nov 25, 2012 6:00 pm Post subject: YS950 S Carb issues
OK Wes, time for another lesson. I took my carb apart and found a couple of issues.
First, the float does not appear to be properly adjusted. At rest with no extra weight on the float there is a distance of 32/64" between the float and the top casting. Before you ask, I found and downloaded a copy of TM 9-1826 and read the part about setting float level. My understanding was that with only the weight of the float itself setting it's position, the float should be adjusted to allow 9/64ths of an inch clearance between the lowest seam of the float and the top casting. Is that correct? If so, mine is way off.... possibly a victim of rough handling during shipment. Also, am I correct that adjusting the float level should be done by bending the attachment point indicated by the black arrow?
Thanks to the info in your album that you shared in an earlier post about a YS637 S carb I also determined that I have the wrong metering rod installed. A replacement is on the way but by chance do you know what effect using a YS637 metering rod in a YS950 carb would have?
I've said it before and no doubt will say it again but I REALLY appreciate you sharing your knowledge and experience with those of us who are still learning.
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
The float setting of 32/64's which is 3 times the correct setting would leave you a wee bit lean in cruise. Although 9/64" is what is called for many gurus will proclaim that the same setting as the 637S of 1/4" is correct. I have run both settings and see no measurable change in performance.
The smaller metering rod would leave you significantly rich.
A really good lesson learned here is: Never assume. We assume the rebuilder knows what he is doing with no real evidence. We assume the correct parts are installed. And we assume the adjustments are correct.
Tim,
Were the correct springs in the correct location? _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Sun Nov 25, 2012 6:38 pm Post subject: YS950S
I agree about making assumptions. I have no illusions about buying used parts but for the most part have lucked out. The fellow I got the carb from has been very helpful and I think I'll still end up with a decent carb for a good price.
Just to be clear, my description of the procedure for adjusting the float was correct?
Regarding the springs, going by your pictures they looked correct. The spring on the pump side matched the dimensions you published in your album. There wasn't dimensional information given for the spring on the metering rod side but eyeballing it looked correct when compared to your photos.
I believe the rebuild kit came from Omix-Ada. Do you have any experience with them? Would you recommend replacing the installed parts with a kit from MWM, Debella or the like?
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Mon Nov 26, 2012 8:51 am Post subject: YS950S
This is for Wes or anyone who can help me out.
I'm still confused about setting the float level. I'm told that not all float valves used in these carbs have a spring in them.... some rely only on gravity and the rise and fall of the float for their position. The valve in my carb has a spring which holds the float high enough above the inverted horn casting that it will take a fair amount of tab bending to bring the float to within 9/64 inch of the face if you don't depress the valve stem by pushing down on the float. In the picture a couple of posts before this one you can see the tip of the valve stem protruding above the blue arrow. When the float is depressed the stem moves into it's housing, closing the valve.
I've been told that in my case, when setting the float level I must gently depress the float enough to close the valve and then take the measurement. is that correct?
Sorry to be such a pest but I'm trying to do this right.
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
Yes that is correct. The spring was added after the carbs first came out to improve seating of the valve during hard off road bouncing around. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Fri Nov 30, 2012 7:32 pm Post subject: YS950 S Update
I'm flummoxed. I installed the correct metering rod and adjusted the float level but I'm still having problems. Bear in mind that the Jeep ran great with my YF carb and that I confirmed spark and fuel pressure.
Anyway.....
•I installed the YS on my Jeep today, double-checked the connections, pulled the choke and hit the starter. After gas got to the carb it fired right up. I used a little throttle to keep it going but very quickly had to cut the choke to half when the engine began to stumble.
•Wanting to warm it up, I let it sit for a minute or so and suddenly the rpm dropped and the engine note became a little ragged. It sounded like it wasn't firing on all cylinders.
•I climbed in and took it out on the grass runway next to my house. I ran it back and forth a couple of times and covered a couple of miles while waiting for some temperature to show on the coolant gauge. I kept it in low and gave it about 75% throttle during this period. It ran OK, no stumbling or bucking although I suspect it wasn't always hitting on all four.
•Driving back to the polebarn, I pulled it into it's spot, let off on the gas and it died. Efforts to restart it were unsuccessful.
•Remembering what happened last time, I pulled the plugs to take a look. This is how they looked after only a few minutes of run time....

•The YS pretty much behaved the same way last time I tried it, fouling the plugs. When I reinstalled the YF carb I had to clean the plugs to get the Jeep to start. FWIW, after driving the Jeep about 20 miles with the YF I pulled a plug and it showed evidence of a clean burn.
•Anyway, I had some new plugs so I installed them.... still won't start, which is a real puzzler. Right now it's on the charger while I try to figure out what to try next.
•I'm inclined to think that since the plugs still fouled out and the engine won't start after being run for awhile, (same as before), the problem has yet to be discovered. I tend to discount the fuel metering rod as being the major cause although I wonder whether there could be an issue with the actual float valve itself. After it died I did loosen the top of the carb a bit and had a little gas seep out around the gasket so there is fuel in there....maybe too much? I tried blowing gently through the fuel inlet as I moved the float fully up and down but noticed that neither position seemed to shut off the airflow. The top of the carb was upside down at the time if that makes a difference.
• The carb is so simple that it would seem that problems like this should be easy to diagnose, but then I'm not a carb guy. Suggestions are welcome
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
No fuel should seep from the bowl to air horn flange when you loosen it. You have a way too high fuel level in the bowl. That can be from a failure of the needle to seal against the seat, it could be a heavy float, it could be an internal fuel leak to the bowl (ie a crack around the seat threads). The problem is clearly in the carb and it could even be plugged passageways from inadequate cleaning during the overhaul.
I would suggest returning the carb for a refund and purchasing a rebuilt carb from a reliable vendor. Midwest Military and The Carburetor shop come to mind. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jun 27, 2011 Posts: 262 Location: "Thumb" of Michigan
Posted: Sat Dec 01, 2012 12:30 pm Post subject: YS950 S Update
Wes,
Good advice. I may just have to go that way. However, being stubborn and having some spare time, I decided to do a little more investigating.
I pulled the carb horn off, removed the float and inspected the needle valve. There was a little crud near the seat which made me think maybe I had found the problem. When cleaned the valve seemed to seal.
To test it, I gently blew through the fuel inlet. The valve appeared to function normally but I noticed that there was air escaping elsewhere. Close examination showed a tiny hole at the base of the threads in the fuel intake casting. I looked at the drawings I had but could not determine conclusively whether that hole was supposed to be there.
Bearing your advice in mind, I carefully inspected all of the carb that I could see with a magnifying glass looking for cracks, but it looked good other than the questionable hole.
Feeling hopeful, I drained some fuel from the bowl, put the carb back together, and hit the starter. It turned over a few times but didn't catch until I pushed the choke off (temp 34°F!) It ran for about a minute before the rpm suddenly dropped and it sounded like it was missing. I shut it down and pulled one of the brand new, never used plugs, I saw that it was already blackened and wet.
Could that tiny hole I mentioned be the trouble or does it belong there?
Tim _________________ Tim Juhl
1952 M38A1
1946 Aeronca L16A Army Liaison Aircraft
To test it, I gently blew through the fuel inlet. The valve appeared to function normally but I noticed that there was air escaping elsewhere.
With finger pressure on the needle pressing it tight to the seat there should be no leakage when you blow in the fuel inlet port.
Quote:
Close examination showed a tiny hole at the base of the threads in the fuel intake casting.
That is about 1/8" to 3/16" in diameter and leads to a hammer in passageway plug. It is a cleanout access point and the hammer in plug may be loose. This will dump fuel under pressure from the fuel pump directly into the bowl irregardless of needle seat position. This plug is illustrated in the M38A1 ORD 9 in figure 03-1 item NN. Only the top shelf rebuild kits come with replacement plugs so that all the cleanout plugs can be removed by drilling and pulling to properly clean the carb's many passageways.
The simple blow test you performed is a "Should have known that test" for your rebuilder. Again all you have found points to a sloppy amateur rebuild of the carb. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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