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Allis Chalmers Discussion Forum
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AC B carb

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Terry DeBoer

02-05-2006 13:06:14




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I am restoring an Allis B for a school project. When I started working on it the pistons were stuck and there was full of water. I am to the point now of trying to get it to start. It is just setting on a running gear and it no longer with the tractor it was in. It has a PTO shaft on it and was used to run augers. It is a crank start. When I tried starting it you can hear the magneto cliking. I checked all of the spark plugs and wires for spark, which they all had and they are in the correct firing order. When you turn the crank you can feel air coming out of the muffler but it won't fire. I got to thinking that the gas wasn't going from the carb to the pistons. THere is a leak in the carb where it can be split into two pieces because the gasket is bad. Would that bad gasket be the cause of the gas not getting past the carburator or is it something else related to the carburator? Any help would be greatly appreciated.

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jeffalex2

02-07-2006 03:14:50




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 Re: AC B carb in reply to Terry DeBoer, 02-05-2006 13:06:14  
If it's not drawing a vacuum thru the carb, you may have an intake or exhaust valve stuck open or not seating properly. More than likely an exhaust valve. Easy check is to take spark plugs out of each cylinder, put finger over hole, and crank a couple of revolutions (with switch off of course). You should get good suction and enough pressure to push your finger away from hole.



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Terry DeBoer

02-10-2006 17:14:54




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 Re: AC B carb in reply to jeffalex2, 02-07-2006 03:14:50  
I've been working on my engine trying to get it to run. I can get it to pop some but that's all. Tonight my dad helped me check the compression. Cylinders 2, 3, and 4 all had around 30-40 pounds of compression. However we couldn't get any compression out of cylinder number 1 by cranking it. We checked the valves and they were seating right. So tomorrow after I get home from work I get to start the fun process over and start taking the head and oil pan off to get the piston out to replace the compression rings. That's what happens when you have a low budget for the rebuild. Oh well. So then once I get it put back together I'm pretty sure it will run.

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Terry DeBoer

02-11-2006 18:47:07




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 Re: AC B carb in reply to Terry DeBoer, 02-10-2006 17:14:54  
I was able to get compression in the first cylinder without having to take either the head off or the piston out. All I had to do was set the valves and then I had compression in the cylinder. The downside is all we got out of it was a pop and 2 inches of flame shooting out of the exhaust. My uncle and I messed with the timing some more and then we got it to sound like it was gonna start. We shot some ether into the air intake on the carb. Then we took the torch and shot some acetylene into the carb. I cranked it a few times and then boom, it ripped the crank right out of my hand. Unfortunalty he had shut the gas off so it didn't run that long. So now I am gonna look for a different carb since this one isn't working. So once I replace it then I should be set.

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jeffalex2

02-06-2006 03:16:45




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 Re: AC B carb in reply to Terry DeBoer, 02-05-2006 13:06:14  
If it's leaking at the bowl gasket, the float valve is letting too much gas in, so, 1st you have to fix the carb. The float should be adjusted such that there is 1 5/32" from the bottom of float to top of bowl, or 7/16" gas in the bowl when it closes. Yes, the gasket needs to be good, but, it wont create a significant enough loss of vacuum thru the throat of the carb to keep it from running unless it's a huge hole. Double check your timing and make sure you're firing at the top of the compression stroke, and not the exhaust stroke (common mistake). To check your vacuum, put your hand in front of the air intake for the carb and crank slowly, it should pull pretty good. Usually if you close the choke, you can hear it suck pretty good. Also, it's been my experience to find that these little B's will flood really fast when choked. Good Luck!

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Terry DeBoer

02-07-2006 19:13:40




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 Re: AC B carb in reply to jeffalex2, 02-06-2006 03:16:45  
I replaced the bowl gasket on the carb and now it doesn't leak anymore. When I closed the choke I could hear it sucking pretty good so then I should have a vacuum. It's timed right and I cleaned the jets and vents in the carb. So do I just have to keep cranking until it fires or is there something that I am missing? I checked to see how much gas was in the carb. It was 3/4" instead of 7/16". So how would I go about setting the float. Also the 1 5/32" from the bottom of the float to the top of the bowl is that with the float pushed up or hanging down?

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jeffalex2

02-08-2006 03:16:44




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 Re: AC B carb in reply to Terry DeBoer, 02-07-2006 19:13:40  
Set with the float pushed up. To adjust, you GENTLY bend the actual float arms, not the valve actuator, until you have the right depth. And yeah, and extra 1/4" in the bowl will make it hard to start...prone to flood. Mine's at about 1/2" of gas. From what it sounds like, if you're getting timed fire and gas, it should come to life for you...Things to try before frustration sets in:

1. If you smell alot of gas while cranking, you're flooded. Pull one or two plugs and see if they are wet, if not, you're OK. Don't leave choke closed while cranking. Close choke, crank once, open choke, crank at least three more times before closing choke again. Keep throttle at about two or three notches above idle.

2. If it floods, either wait a couple minutes or close the throttle all the way, and crank a few times.

3. Also, you can try tweaking timing 1/4" adv or ret by loosening mag.

Sounds like fun, wish I was there to help.

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Terry DeBoer

02-06-2006 18:07:20




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 Re: AC B carb in reply to jeffalex2, 02-06-2006 03:16:45  
I double checked the timing and it was firing on the compression stroke and not on the exhaust. I checked for a vacuum but I think that it isn't creating the vacuum. I took the carb apart and cleaned the junk out that was in the main jet. I haven't set the float yet. The bowl gasket leaks enough that gas drips out of it pretty fast so the hole might be big enough that it can't create the vacuum. I am going to replace the float, needle, seat and some other things and put a new gasket on. I am hoping that this will solve the problem.

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Dick L

02-05-2006 15:38:22




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 Re: AC B carb in reply to Terry DeBoer, 02-05-2006 13:06:14  
Air coming out the exhaust does not automatically mean you have vacuum at the carburetor. The gasket at the bowl could be the problem as well as any of the gaskets from the head down. Then the carburetor has to be clean with all the jets and vents clear.



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