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Re: 620 carburetor problem

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Mike Aylward

03-15-2013 20:00:06

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Ron, quite possibly your idle circuit still has a small amount of debris in it. A piece of dirt or rust the size of a piece of pepper will mess up these carburetors. It's also possible the metering valve "umbrella" has stuck to it's seat and is limiting the fuel flow to the two sides. I have also seen the seat get turned which blocks off the holes in the seat. Mike

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55 50 Ron

03-16-2013 07:27:17

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 Re: 620 carburetor problem in reply to Mike Aylward, 03-15-2013 20:00:06  
Mike, You mentioned metering valve "umbrella". I'm not familiar with that description. Would you explain that a little more in terms of the parts breakdown in the parts book? Thanks.

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Mike Aylward

03-16-2013 11:00:27

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 Re: 620 carburetor problem in reply to 55 50 Ron, 03-16-2013 07:27:17  
Ron, the center metering valve on a Duplex carburetor has a riveted-on tapered stem I call an umbrella. This fits down into a tapered seat in the carburetor body. This seat is commonly made of brass and has two holes that are "square" to the carburetor. These holes feed additional fuel to the main nozzles in addition to the fixed jets. The book suggests to bottom the tapered metering valve in it's seat and then back it off an appropriate number of turns (commonly in the range of 2 to 2.5 turns out). The "umbrella" is made of steel and as mentioned is riveted to the metering valve. It is not uncommon for the seat to be turned in too hard and the umbrella sticks to the valve. It then comes apart from the metering valve and then you have a mess. I have seen this happen many times and have also noticed the seats turning in the carburetor bodies. The seat has two marks on it that look like a screwdriver slot (they aren't). If the seat is indexed correctly in the body these slots will be "square" to the carburetor as well as they line up with the holes. If the seat has moved the carburetor will not allow the tractor to run or pull like it should. This is a very often overlooked item on a Duplex carburetor. Hope this helps. Mike

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03-16-2013 06:07:02

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 Re: 620 carburetor problem in reply to Mike Aylward, 03-15-2013 20:00:06  
I agree with Mike on the idle circut as being the most likely problem if just choking a little makes it run alright, and to do a good job cleaning them out,you need to get the steel balls out for each circut. By trying to blow air through,you should be able to tell if it is just one side or two you need to clean, and which one. Good luck

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