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Allis B rough idle

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Allan Noyes

03-21-2005 16:43:11




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I am working on an Allis B . Carb and mag have been rebuilt and timed correctly. Valve clearences are right. Engine runs fine other than it won't idle smooth without the choke nearly shut and the idle adjustment screw closed. It has a Zenith 62 carb and Fairbanks FMJ mag. Anyone have any ideas?




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Texas Denny

03-22-2005 10:41:56




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 Re: Allis B rough idle in reply to Allan Noyes, 03-21-2005 16:43:11  
Everyone is right. Your problem can be any of an assortment. Bad valves will cause rough idle. Bad plugs, even though brand new, can cause such a problem (happened to me with new Champions on a WD with M&W pistons and sleeves right after rebuild). But my first effort would all tend to gas and the intake manifold. First, are you sure all of the channels in the carb are clean. Rebuilding is more complicated than putting a new kit in it. Those channels all must be open if the carb is to wotk correctly. Since you say it runs fine at high rpm and bad at idle, I'd suspect the idle circuit as being faulty. I'd also look over the intake manifold where it mounts to the block. If any of the gaskets are leaking, it will run better at higher rpm than low. Also, is the gasket between the carb and mainfold good?

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Steve,Ga

03-22-2005 10:38:26




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 Re: Allis B rough idle in reply to Allan Noyes, 03-21-2005 16:43:11  
that choke needing to be part closed always meant the valves were not sealing,in my experience,there isnt a vacuum on the intake stroke strong enough to make the carb work 100%.I have used em for years that way.



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Dick L

03-22-2005 07:52:04




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 Re: Allis B rough idle in reply to Allan Noyes, 03-21-2005 16:43:11  
Way more questions than answers. Has the valves been reground and well as the seats? Does it have new plugs? If it has new plugs do you have another set to see if all the plugs are firing properly? I have in the past fought an idle problem only to find a new plug was the problem?
The other questions are valid things to check. You can have three or more tractors with the same idle problem and a different solution for each tractor.

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steve(ill)

03-21-2005 19:17:34




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 Re: Allis B rough idle in reply to Allan Noyes, 03-21-2005 16:43:11  
if you need the choke on to idle, then you are not getting enough gas. shutting down the air supply causes it to suck more fuel. how does it run at 1600 rpm? i am guesing you still have a carb problem. how about the float level? was the bowl soaked to clean out the jet holes?



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Russ1

03-22-2005 07:18:05




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 Re: Allis B rough idle in reply to steve(ill), 03-21-2005 19:17:34  
Could be an intake manifold leak allowing air into the engine after the carburator.



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Allan Noyes

03-27-2005 09:32:09




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 Re: Allis B rough idle in reply to Russ1, 03-22-2005 07:18:05  
Thanks to all who replied. Seems to be a combination of all problems combined. Replaced manifold gasket, moved the throttle plate futher away from idle port in carb. It runs better but a head overhaul would probably do the trick.



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