B carburetor question
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Category: Allis Chalmers
Forum Name: Farm Equipment
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=15375
Printed Date: 04 Feb 2025 at 8:47am
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Topic: B carburetor question
Posted By: Scott in MA
Subject: B carburetor question
Date Posted: 18 Jul 2010 at 6:35pm
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Hi all- My reprint owners manual shows only two adjustment screws in the carburetor - one for air/fuel mixture and the other for idle adjustment. Both of these are on the tractor side of the carb (the side you can't unless its off the tractor). Mine has a third that isn't in the manual. Can anyone tell me what it is and how I should adjust it? It's the screw that my pen is pointing to. I have one guess. The carburetor in the manual had a shut off valve on the bottom, which mine doesn't. Could this be a fuel flow on-off valve? It doesn't have a whole lot of threads, so its range of adjustability isn't great. I appreciate any help!  |
Replies:
Posted By: Scott in MA
Date Posted: 18 Jul 2010 at 7:10pm
| There is an idle adjusting screw and an air/fuel mixture screw on the other side. |
Posted By: CTuckerNWIL
Date Posted: 18 Jul 2010 at 7:13pm
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I was looking at the zenith picture which has the idle mixture somewhere near that position. You carb is an MS so according to the book I'm looking at "the main jet adjusting needle is located on the front upper portion of the bowl", which is what you are pointing to.
------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: Rick of HopeIN
Date Posted: 18 Jul 2010 at 7:20pm
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Fuel shut off valve should be on the sediment bowl or under the tank. If you have trouble try eliminating that filter. I could not get mine to run right until I went back to a plain sediment bowl screen and no line filter..
------------- 1951 B, 1937 WC, 1957 D14, -- Thanks and God Bless |
Posted By: Dick L
Date Posted: 18 Jul 2010 at 7:36pm
| The screw your pen is pointing at is the power jet adjustment screw. That carburetor is not the one intended for your B but will still work. That is the reason the idle adjusting screw is not handy to adjust. With the throttle wide open you adjust the power jet to run the highest RPM and then turn it in until you get a very slight drop in RPM's. You set that after you have the idle adjusted normally. With the heavy spring holding the butterfly closed most likely means you have other adjustment problems that someone has overcome with the spring rather than make the proper adjustments. |
Posted By: CTuckerNWIL
Date Posted: 18 Jul 2010 at 7:40pm
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The screw on the back side that you can't see is the throttle stop screw and limits the travel of the throttle plate. The idle adjusting screw is an air fuel mixture screw for the idle circuit. There is no fuel "shut off" on the carb. I was going to suggest what Rick did too. Get rid of the rubber fuel line and the automotive fuel filter. The tractors worked fine for 50 years with a sediment bowl and a plain steel line. I just had to replace a rubber fuel line temporarily because the inside of it turned to mush and it collapsed. ------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: Scott in MA
Date Posted: 18 Jul 2010 at 8:31pm
| Thanks for the information. This B is a non-runner. How should that Power Jet screw be adjusted to get it started? Is the adjustment crucial to get it started? |
Posted By: CTuckerNWIL
Date Posted: 18 Jul 2010 at 9:53pm
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Turn it all the way in without forcing it to bottom and back out 1.5 to 2 turns. ------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: Scott in MA
Date Posted: 19 Jul 2010 at 9:01am
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Unfortunately, I don't have enough thread on the screw to back it out that far. Once you turn it in all the way, you have barely enough thread to turn it back 3/4 out.
I'm wondering if this strange little screw is responsible for the tractor's refusal to start.
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Posted By: CTuckerNWIL
Date Posted: 19 Jul 2010 at 9:08am
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Either the screw has missing threads or the casting is stripped out. I would remove the screw and see if it looks like it has threads on the full length and if not find a replacement screw. ------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: Steve in NJ
Date Posted: 19 Jul 2010 at 9:59am
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Another thing you want to take into consideration is that big ole' automotive type fuel filter hanging down off the carb. That particular fuel filter is used for fuel pump equipped engines, and can slow incoming fuel to that carb especially with that roller coaster fuel line attached to it. You have to remember, these engines are gravity fed for fuel, so fuel lines with whoop-de-doo's in them and large automotive fuel filters, are not the ticket for smooth flowing gravity fed fuel systems. Use a gravity fed type fuel filter that's found on small engines with a straight level steel fuel line from the tank or sediment bulb. This will give you a straight smooth fuel flow to the carb, so when the engine goes under load to work, there is enough available fuel in the fuel bowls to supply for your fuel demands. The engine will act the same way with a very low float level... HTH Steve@B&B |
Posted By: Dick L
Date Posted: 19 Jul 2010 at 11:49am
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If it were me and I sure know that you aint me, I would get a Zenith carburetor from some where that goes with the tractor. I would start going thru all the spec details while waiting on the carburetor. Make sure it is firing on time (TDC) when cranking it over slowly, check the compression, check valve clearance, check and set the cross over arm, make sure there is a good flow of fuel from the tank to the carburetor, ditch that heavy spring in the picture. A surge spring is very light weight and hooks up on a manifold stud not back like the one in the picture. Success is achieved by having the above spot on before you try to make smoke. You can check compression on a dead tractor by checking vacuum with the palm of your hand over the carburetor intake while spinning it over with the starter. Even if the carburetor is off you can check at the manifold where the carburetor bolts on. That is close enough to know if it will have enough compression to run. |