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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Fri Jul 24, 2020 8:49 pm Post subject: YS637 Carburetor Air Horn Question |
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I am in the process of testing out a rebuilt L134 engine with a rebuilt YS637 carburetor. Engine starts fine but carburetor floods after a couple minutes of running.
I have been working through the troubleshooting guide as well as Wes's list to solve.
Fuel pump pressure is 6 1/2 psi at carburetor - I know this is higher than the spec of 4 1/2 to 5 psi. Is that difference material?
Float is is sealed - no cracks - no leaks
float setting is 1/4 inch per spec.
Float lip is smooth no burs or grooves
To see if the float needle is sealing I removed the air horn and tested float circuit by connecting it to the pump. I can stop the fuel flow when the float is raised to the proper position however fuel continues to pour through a small pinhole in bottom of the air horn casting that houses the inlet screen.
Is that pinhole a defect in my air horn casting or is it some form of minimum flow bypass?
Thanks,
John _________________ John
https://1952m38cdn.wordpress.com
1952 M38CDN F-101165 CAR 52-31204 |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16256 Location: Wisconsin
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Sat Jul 25, 2020 8:33 am Post subject: |
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Thank you for responding Wes.
Yes I have downloaded TM9- 1826A and have not found any mention of this hole nor a figure showing it. In particular I would have expected it to be labeled in Figure 56 on the float circuit. Pinhole is located in the bottom of the casting that encloses the fuel inlet screen. Hopefully it is visible in the following photo of the base of the air horn casting. Its located at the transition of the first and second concentric cylindrical sections that enclose the strainer.
Again my thanks for your help. _________________ John
https://1952m38cdn.wordpress.com
1952 M38CDN F-101165 CAR 52-31204 |
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mdainsd Member
Joined: Oct 20, 2017 Posts: 444
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Posted: Sat Jul 25, 2020 10:18 am Post subject: |
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That pin hole doesn't seem right. It looks to be so small that it might take a bit of time to overfill the float bowl.
I have an airhorn in my hand as I write this as one of todays tasks is to put together another M38 carb. There is no hole there in mine. _________________ '52 Dodge M37, '42 GPW, '48 FrankenJeep CJ2A/M38, '50 CJV-35(U), '51 M38, '42 WC-57 Command Car, '44 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlights, John Deere M-gator, '44 White M3A1 Scout Car |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16256 Location: Wisconsin
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Sun Jul 26, 2020 8:05 pm Post subject: |
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I rechecked pressure and confirmed its 6 1/2 psi. I noted I have motor oil in my fuel especially the first few strokes.
Looking through your archive now, Wes.
Thanks,
John |
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wesk Site Administrator
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Mon Jul 27, 2020 3:27 pm Post subject: |
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I have a rebuilt AC Series CU or CY fuel and vacuum pump (no primer handle) and I have a 9/16" thick spacer between pump and block.
Thanks,
John |
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wesk Site Administrator
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Tue Jul 28, 2020 2:06 pm Post subject: |
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Wes,
Four digits on flange are 9585.
Some photos of fuel pump installed for reference.
Thanks _________________ John
https://1952m38cdn.wordpress.com
1952 M38CDN F-101165 CAR 52-31204 |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16256 Location: Wisconsin
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Tue Aug 04, 2020 9:09 pm Post subject: |
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Wes,
Thank you again for your assistance.
I disassembled the pump to see if the technical bulletin has been complied with. There is a 1/8" diameter hole drilled in the deck of the body and the oil seal has been removed.
The diaphragm looks to be in good condition - no rips or cracks.
I noted the spring retainer was missing on the diaphragm side although I don't see how that would contribute to higher fuel pressure or oil drawn into fuel.
Last photo shows oil on fuel cover.
Your guidance welcome.
Thanks, _________________ John
https://1952m38cdn.wordpress.com
1952 M38CDN F-101165 CAR 52-31204 |
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L84dinner Member
Joined: Jul 06, 2014 Posts: 25 Location: Mississauga, Ontario
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Posted: Mon Aug 17, 2020 3:19 pm Post subject: |
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Just wanted to follow up and state that I was able to effectively plug the pinhole in the airhorn and it now starts and runs smooth without further flooding. Still have not resolved the fuel pump pressure question although have confirmed rebuild was done correctly. I am going to check my gauge before I take any further action.
Thanks for the help.
John |
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