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1947 8N CARB. PROBLEM

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ROBERT RIGGS

07-24-2006 19:23:52




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Hi, everyone I finally got my 8N running great. The problem is it only runs great with the main carb. adjustment srew totally out. CAN ANYONE TELL WE WHY AND WHAT TO DO THANK YOU.




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Jerry/MT

07-25-2006 10:13:56




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 Re: 1947 8N CARB. PROBLEM in reply to ROBERT RIGGS, 07-24-2006 19:23:52  
Yout carb is a balanced pressure deigned carb. There is a small hole in the air horn casting near where the choke is at That's the balance tube that vents the fuel bowl to the air horn and allows the fuel/air ratio to be independent of the air cleaner restriction. Make sure that the balance passage is clear and your problem will be solved. You can also notch the gasket but you're better off to get the ballance tube open.

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ZANE

07-25-2006 03:54:42




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 Re: 1947 8N CARB. PROBLEM in reply to ROBERT RIGGS, 07-24-2006 19:23:52  
The carburetor bowl vent is plugged.

Unplug the vent or drill a tiny hole in the top of the carburetor or cut out a 1/4" place in the gasket between the two halves of the carburetor.

Only thing that causes the symptoms you are having.

Zane



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ROBERT RIGGS

07-25-2006 07:27:30




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 Re: 1947 8N CARB. PROBLEM in reply to ZANE, 07-25-2006 03:54:42  
Thank You, I had not thought about the vent going to try taht now. As far as the bad batch of carb. rebuild kits I had taken mine apart again and did notice differnt size jets came with the kit. Did not get it runninng good till i put the old parts back in. Except the main adjustment screw.



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ron,ar

07-24-2006 20:25:08




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 Re: 1947 8N CARB. PROBLEM in reply to ROBERT RIGGS, 07-24-2006 19:23:52  
Would you like to have another one like it:^)



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K.LaRue-VA

07-24-2006 20:19:18




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 Re: 1947 8N CARB. PROBLEM in reply to ROBERT RIGGS, 07-24-2006 19:23:52  
Second one of these in a week, I am beginning to wonder if there is a bad batch of rebuild kits out there with the wrong parts??? Look for questions posted by ron,ar currently on page 2 and page 4 for lots of information.

If this started with a recent rebuild, I am starting to think you might want to try swapping some of your new parts with the original ones, especially things like jets and the main metering screw.

I bought a used carb off ebay a while back and rebuilt-it for my 8N. It worked great and I rebuilt the original one to keep as a spare. If anything like this happens to me at least I can swap carbs to see if the problem goes away.

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ron,ar

07-24-2006 20:59:18




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 Re: 1947 8N CARB. PROBLEM in reply to K.LaRue-VA, 07-24-2006 20:19:18  
I did not change the jets, just the throttle shaft, seals, float needle valve/seat and gaskets. I did a little more checking this afternoon. The actual seat that the long high speed needle contacts in the bottom appears to be just a brass/bronze tube pressed into the housing. There is no slot for a screwdriver to remove it with and it is almost flush with the bore it goes in. I would like verification on this from someone here, maybe they could tell me what that little tube looks like as far as any seating/contact area is concerned. I suspect that the needle has been run down too hard, expanding that tube/seat. When this happens the needle goes down into this tube acting more like a plug than a tapered valve and seat. It is only when the needle is backed out almost to the max that it lifts OUT of the tube instead of gradually tapering off a seat. Then the engine recieves enough fuel to run right but it leaves no room for adjustment, it becomes an open or shut, all or nothing valve instead of a metering valve. This is just my opinion after measuring the depth of the little tube down in the carb and the length of the needle, while observing how far the needle sits in the top half while screwed all the way down. I see no way to get that brass/bronze tube out of its bore as there is no access from the bottom even with the drain plug out.

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Farmer(Ga)

07-24-2006 22:55:50




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 Re: 1947 8N CARB. PROBLEM in reply to ron,ar, 07-24-2006 20:59:18  

Ron, Thats the way i've been thinking ever since you first posted,My first thoughts was the neddle screwed down to far and tight. May have to be drilled out. James



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Dixon

07-24-2006 23:26:01




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 Re: 1947 8N CARB. PROBLEM in reply to Farmer(Ga), 07-24-2006 22:55:50  
Ron,heres an idea from a friend of mine.Run the tractor on a different gas tank (gravity
feed). If the carb is clean he is not getting enough
fuel feed. It could be collapsing fuel
line or a problem with his tank. Tom
also Ron check the actual rod to see if it could be bent thereby not seating properly until raised up.



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