Phishook
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I've got an older John Deere with an issue that needs resolved soon.
It'll start and idol fine. Put it on jack stands and it will run 4-5000 rpms smooth, with a few boosts higher in the 6-7k range.
As soon as you put in on the ground I can get maybe 100yrds and it starts cutting out at speeds over 1/4 to 1/3 throttle. If I let off soon enough it catches itself, but I have to run it just above idol back to the shop.
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Took the carb off (again) and it looks clean, but we cleaned it again. I was thinking the main jet had some dirt but that wasn't it. 130 and 135psi in the cylinders, new fuel lines and clamps, new fuel pump, new plugs, new trac, rebuilt the suspension, fresh paint) So you see, I'd really like to get this out of the shop.
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TheguN
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hard to say for sure! sounds like everything is good until you put a load on it! maybe a few things! I assume it is a points system! try cleaning and checking clearances there! that is where i would start then check your coil!
this is under the assumption you have checked to see all the fuel related items are good!
is the diaphragm good in the lift pump?
Air fuel mixture good! not to rich and the motor is loading up!
hope this gives you some ideas on things to check! cant really say for sure without running it for myself!
lots of smart people here! hope some one can help!
Good luck! 
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Hard Water addict
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What kind of carbs are on it???
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backlasher
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I would start by checking the fuel pick-up line. They usually have a weighted filter on the end, so check if it's plugged or off and not staying down in the tank. Also I would check the carb vent lines to make sure they are clear. It sounds like a fuel starvation problem, so if these don't do it, one of the carb passages are plugged. Maybe the nozzle or needle and seat. Good luck.
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Phishook
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1980 JD trailfire with a 440 (ta440a)
Sorry, I should have said it has a CDI box. Is there a way to check the ignition coil?
Single Makuni VM slide carb. But I really want to say the carb is OK
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johnie walleye
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sounds like your cdi box to me or a coil. But I'm leaning towards the cdi. I had a dirtbike that did the same thing! You could ride it around warming it up and even trail riding but when you needed the juice like climbing steep hills it acted like a fouled plug just no beans.
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Pain heals
Chicks dig scars
Glory lasts forever
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mallard_militia
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I see you were in the carbs. How did the needle and seat look on your float? You could be loading up with fuel. Are you plugs really wet? Does it run half choked? Does it backfire?
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Never take life too seriously.
Nobody gets out alive anyway.
Edited by mallard_militia (02/02/09 05:18 PM)
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Phishook
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Quote:
I see you were in the carbs. How did the needle and seat look on your float? You could be loading up with fuel. Are you plugs really wet? Does it run half choked? Does it backfire?
no backfire at all, new plugs haven't been ran long enough to show color but the old ones were dark tan and dry after running.
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Hard Water addict
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When it starts to bog with it keep running if you choke it?? If so you have a plugged jet in there.
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big G
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Its been awhile since I tackled a bogging sled issue, but I would definitely lean towards a carb issue. In the jack stands, if you pin it, it will run fine ? Why it does not bog down on the jack stand does not make sense. If it did, then its time to get the starting fluid and see if that keeps it running instead of bogging. Good luck
big G 
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You can tell how big a person is, by what it takes to discourage them! "Hooks"
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trumar
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Just fix a polaris with the same EXACT issue ....
water in the fuel, removed tank and cleaned, now runs as good as a Polaris can 
Just a thought
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"When it comes to family-Sometimes it not all about fishing" ~Trumar 2009
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Phishook
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Quote:
When it starts to bog with it keep running if you choke it?? If so you have a plugged jet in there.
tried this, it didnt change.
I'll check the tank filter and fuel tomorrow. Be nice if this was all it was. If not my guess is the cdi or ignition coil. I've read mixed things about the cdi boxes. Some say that they are either bad or good.
Edited by Phishook (02/02/09 07:28 PM)
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Jack Pine
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I am not a mechanic but I had a similar problem with an old Aortic Cat. The fuel line had broken down into pieces. The hole in the line allowed debris to bypass the filter. It would start fine but when you revved it up it would suck the little chunks of fuel line in and plug the line. If you let it sit a few minutes, the suction would release the debris and it would start again but only at low speed.
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Sled Cutting Out
