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Allis Chalmers Discussion Forum
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AC 1939 B

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B confused

08-25-2007 10:11:50




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This a crank start model that progressively got harder and harder to start. To a point now where I cannot start it without towing. Then it starts right up.
Replaced points and condenser.
cleaned carb 3 times
set and rechecked timing.
Carb is Zenith, not sure of settings, starting at 1 1/2 turns out on both main jet and idle. Which way is lean/rich?
Any ideas on what I am missing?




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greatwest

08-27-2007 20:55:10




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
I've got a ca that I have to choke occasionally to get going via hand cranking... If it starts and quits first crank I have to choke it once or it will not start. Try cranking with choke on first time then with choke off check to see if choke is drawing fuel into cylinders. otherwise as mentioned before,could be mag or valve settings/intake manifold gasket? Maybe check compression too and do a leak-down test. A belt is also a handy thing for starting between two belt pulleys!

Good luck, Great west

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J.C.in AZ.

08-26-2007 07:41:04




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
I remember when I was a Kid[long time ago].My Dad had a MM U which did the same thing for quite a while and it caused a lot of problems for every one involved. It was a new 1952 U and he had it only a couple of months doing chores etc. as it was in the summer and field work was over. He had several fights with the MM Dealer [who was his friend] had the tractor back to the Dealership several times and one day my Uncle came by and got to fooling with it,took the sediment bowl unit off the gas tank and only half a stream of gas came out.Took the tank off and dumped the gas in a big wash tub and several Oat heads came out with the gas. He figured that some time when the Tractor was in the Crib drive some one[me] put gas in it with a 5 Gal. Can and Funnel and these Oats must have dropped from the overhead bin into the Funnel and then into the Tank. These Oat Heads would float around and some times would fill the Tank outlet and stop the flow of Fuel. Problem fixed. I never got in trouble but I always remembered that and any time a tractor of mine ran bad I always checked the Gas Tank outlet first.

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Ted_in NE_ OH

08-25-2007 21:49:59




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
A flooded carb will do this.



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JMS/MN

08-25-2007 16:46:45




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
Time to rebuild the magneto, if so equipped. We had the same problem decades ago on two tractors when I was growing up. Could turn the starter all day long and not start, pull it 3 feet and it's running! WC and a C.



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B confused

08-25-2007 10:46:22




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
Thanks,

Spark appears hot and blue, will recheck.

How about carb adjustments, which way for lean/rich?



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CENTAUR

08-25-2007 13:21:33




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:46:22  
First get it started again.Then adjust the throttle stop screw to a low idle.THEN TURN THE IDLE ADJUSTMENT IN AND OUT TILL YOU GET THE MAXUUM RPMs.You will go back and forth till you get it dowwn to idle speed you want.The main jet or what is called the high speed circuit is not doing anything while you are doing the idle.Now you are ready to adjust the main jet.Open your throttle to a high working speed and again adjust for maxuum RPMs.This procedure will work on anything(updraft or downdraft)The magneto articles also apply. CENTAUR

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old

08-25-2007 12:52:49




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:46:22  
On the hand crank types if the impulse isn't working as it should you will not get it to start by hand. On the carb. The top screw is idle and as you turn it in it gets richer out leaner. On the main jet as you turn it in it gets leaner and out to make it richer. Also when you took off the cover/cap of the mag to do the points are you sure you got the gears lined up correctly if not then that can be your problem. Do you have the manual for the mag?? If not send me an e-mail and I can send you one I have in my computer which may help you figure out the problem

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cbp

08-25-2007 11:18:22




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:46:22  
The impulse coupler will gives it a kick at very low RPM, such as cranking speeds but below idle speed. That's more than just having a good running spark. It's what makes crank starting work well. If you have the mag off you'll be able to hear the click as it winds up and releases, even turning slowly by hand. If it's not actuating, I'm not sure you could crank start it.
I believe you turn out for more air to lean the mixture but it's been a long time, someone else should confirm that.

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cbp

08-25-2007 10:37:00




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 Re: AC 1939 B in reply to B confused, 08-25-2007 10:11:50  
Could be your impulse coupler in the mag is not functioning anymore. It would be very hard to crank start without that hot initial spark.

Valve adjustment can also create the same sort of problem but you'd have to pull it around in circles quite a bit before the attempts to fire warmed them enough to enough to expand the steel. In other words, it wouldn't kick right off if that were the problem. If it fires instantly when you pull start, I'd bet on the mag issue.

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