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JD-50 HELP!

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Bob

02-18-2002 11:49:52




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Have a JD-50 that slow idles fine but runs rough or one one cylinder under fast idle or load. The original Wico distributor(stopped running)was replaced several years ago with a Delco system. I had just finished washing an attached tiller after tilling the garden. I got on the tractor which was idling and gave it throttle only to hear it run on one cylinder. It had been running under load just fine. I've changed spark plugs (both Champion D-21s and AC C88s), cleaned the carburetor (DLTX-75), and checked the valve lash settings (.022 hot). I've tried a DLTX-81 carburetor and the distributor from a running JD60, and also tried another coil. It starts and runs great at idle speed but runs rough with no power (will hardly pull itself) at speeds above idle. The carburetor idle screws will alter the idle but the mixing screw seems to have no effect at all with either carburetor. I've also tried the timing from full retard to full advance. Nothing I do seems to make it run better. The valve springs seem to have equal tension (I have not taken them off to test them - can these be taken off without removing the head?)and the cylinders show 80 - 90 PSI. I don't claim to be a mechanic, just a tinkerer. I would appreciate any suggestions anyone has.

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Clooney

02-18-2002 13:41:24




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 Re: JD-50 HELP! in reply to Bob, 02-18-2002 11:49:52  
Bob, you have covered most of the bases.
~First pull the drain plug on the bottom of the carb & then open & hold down the knurled knob on top of the fuel strainer (oil pressure fuel shut off only) & see if you have a pencil sized stream of fuel for at least 30 seconds, if so then install new spark plug & coil wires (solid core wires), if not clean the tank fitting & or strainer screen.
~If still no improvement, try a new dist cap & rotor, unless you used the cap & rotor from the 60 to test. ~It sure sounds like spark plugs but if you have tried 2 NEW sets it must be something else & you have eliminated most common things like carb, distributor & spark plugs.
~You can remove the valve springs with the head on if you put an air supply on the spark plug hole to hold the valves closed, but you should be able to feel a real weak valve spring without pulling them.
~The compression sounds a little low unless you have an all-fuel tractor or ran the compression test with the throttle closed.
~If nothing else gives you an improvement, try running with the air cleaner disconnected.
~It might not hurt to sniff in the oil fill to see if the crankcase is full of gasoline from a leaking diaphragm in the fuel shut-off.

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Bob

02-19-2002 16:49:05




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 Re: Re: JD-50 HELP! in reply to Clooney, 02-18-2002 13:41:24  
I took a compression ckeck with the throttle open and with a guage that screws in - both cylinders read 105 PSI. Disconnecting the air filter shows no improvement. Both spark plugs show really bad carbon deposits after running about 10 - 15 minutes. The choke on both carburetors open as they should. I've also tried fresh fuel. So far I think I've eliminated electrical and carburation but the fouling certainly indicates a rich mixture or poor spark. Is there anything left?? What about a hotter plug? If so what number would a hotter plug be? I MUCH appreciate all your time and advice!

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Clooney

02-20-2002 14:37:26




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 Re: Re: Re: JD-50 HELP! in reply to Bob, 02-19-2002 16:49:05  
Bob, you don't have much left to try.
~You might try removing the exhaust pipe from the manifold & muffler then bolt it back on with the pipe not in the muffler to see if there is a blockage in the muffler like a cocked baffle or other restriction.
~I suppose it's possible you have a heavy build up of carbon on the valve stem/valve head area blocking the intake or exhaust flow. I have seen that so bad on automobiles that the carbon completly fills the valve pocket but have not seen it on a 2-cylinder tractor (it is very possible though)
~Probably wouldn't hurt to pull the rocker cover & see if the valves are all opening the same amount (a worn cam could be affecting the valve lift on one or more valves)
~Be absolutely sure the heat valve is turned to either hot or cold & not in between as that will block exhaust flow.

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Bob

02-21-2002 13:48:39




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 Re: Re: Re: Re: JD-50 HELP! in reply to Clooney, 02-20-2002 14:37:26  
Thanks for your follow-ups, especially about the heat valve. It's a little embarassing to admit, but the heat exhaust valve clamp was loose and allowed the valve to turn slightly. It was only about 15-20 degrees off but apparantly enough to cause an exhaust block in the left cylinder. The 50 runs great after straightening it. Another lesson learned! Sometimes I think my head isn't big enough to learn all I need to know. I now have a JD B and a JD60 to put back together after cannabalizing for parts. Thanks again for your GREAT advice!!!

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Clooney

02-21-2002 16:28:26




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 Re: Re: Re: Re: Re: JD-50 HELP! in reply to Bob, 02-21-2002 13:48:39  
Bob, I'm glad you have it up & running correctly as we were running out of suggestions.



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Ron

02-18-2002 19:43:30




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 Re: Re: JD-50 HELP! in reply to Clooney, 02-18-2002 13:41:24  
Yes, as Clooney says....dis-connect the air cleaner....I have had problems with "Mud Dauber" nests pluging the air inlet.. Makes the engine pull engine oil into the intake.....Then they can drive you Crazy....!!!!



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Bob

02-18-2002 16:24:00




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 Re: Re: JD-50 HELP! in reply to Clooney, 02-18-2002 13:41:24  
The fuel flow is good. Different plug wires, rotor cap, distributer cap, points, and condenser were changed. I did the compression test with the throttle closed and also with a tester that you hold on rather than screw in (I did this while my wife cranked as I don't have a 18mm fitting for my tester - this may also account for the reading!?!?) Disconnecting the air cleaner sounds good! I'll try this tomorrow. No gas in the crankcase. I agree that it sounds like spark because the plugs get carboned up after running for awhile. I also tried Autolite 386s. I much appreciate all the info I'm receiving!!

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Rod

02-19-2002 07:06:21




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 Re: Re: Re: JD-50 HELP! in reply to Bob, 02-18-2002 16:24:00  
Pull the pot metal choke lever off and make sure it is installed correctly and spring is not broken,since you say the plugs get black you must be getting plenty of fuel. Maybe the choke is not coming off all the way?



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Rod

02-19-2002 07:05:59




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 Re: Re: Re: JD-50 HELP! in reply to Bob, 02-18-2002 16:24:00  
Pull the pot metal choke lever off and make sure it is installed correctly and spring is not broken,since you say the plugs get black you must be getting plenty of fuel. Maybe the choke is not coming off all the way?



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Bob

02-19-2002 17:04:03




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 Re: Re: Re: Re: JD-50 HELP! in reply to Rod, 02-19-2002 07:05:59  
The chokes on both carburetors work as they should. I checked when I had the air cleaner disengauged. This one has me completely stumped. The carboned up plugs indicate a rich mixture or weak spark but I think I've eliminated those. I'm beginning to think valves but they also seem to be working properly. I MUCH appreciate your time and advice!



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G Taylor

02-18-2002 13:05:09




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 Re: JD-50 HELP! in reply to Bob, 02-18-2002 11:49:52  
What is the coolant temp, is the manifold set hot or cold & where are the main & idle mixture screws set to?



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Bob

02-18-2002 16:13:55




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 Re: Re: JD-50 HELP! in reply to G Taylor , 02-18-2002 13:05:09  
Coolant temp is OK. Manifold set to heat. Both the idle screws and mixture backed off 1&1/2.



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G Taylor

02-18-2002 17:22:54




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 Re: Re: Re: JD-50 HELP! in reply to Bob, 02-18-2002 16:13:55  
Two out of three trouble makers covered. What is the actual coolant temp in degrees F, better yet measured temp with a candy thermometer at the rad filler? What is the actual voltage on the coil when the points are closed? Some tractors just seem to need the electronic converion to fire the plugs even in stock configuration. How old is the fuel & what temp was it stored at?



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Bob

02-19-2002 16:57:43




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 Re: Re: Re: Re: JD-50 HELP! in reply to G Taylor , 02-18-2002 17:22:54  
I tried fresh fuel - no change. The temp runs about 175 in the radiator after idling awhile. The voltage on the battery side of the coil is 12v running, or stopped with either the points open or closed. Voltage on the distriberator side is about 7.5v running. The tractor does not have the 6v/12v overide at start. It has a straight 12v from the battery with a 12v coil. The plugs get pretty sever carbon deposits after idling a short time. I MUCH appreciate your time and advice.

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G Taylor , clue from Clooney

02-19-2002 19:44:45




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 Re: Re: Re: Re: Re: JD-50 HELP! in reply to Bob, 02-19-2002 16:57:43  
Was just thinking of Clooney's description of the Deere spec carb using a port from the carb throat to the fuel bowl. At light loads this reduces pressure forcing fuel up the metering jets/ports, leaning the mixture as required. The next step would be a fresh float bowl gasket after a through check for cracks,dents old gasket material etc.If the bowl is under full atmospheric pressure this would explain the situation. Do the plugs stay "cleaner" longer if the idle is leaned out to occassional misfire or almost hesitating when the throttle is advanced?

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Bob

02-21-2002 14:00:44




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 Re: Re: Re: Re: Re: Re: JD-50 HELP! in reply to G Taylor , clue from Clooney , 02-19-2002 19:44:45  
Your comment on where was the exhaust valve set was right on target. I checked it out and it was on hot but slightly cocked about 15 - 20 degrees but apparantly enough to cause an exhaust restriction in the left cylinder. Your comment really rang bells when Clooney commented that the valve had to be set just right. The 50 runs great now. Many thanks for your input.



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Guy

02-18-2002 12:41:24




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 Re: JD-50 HELP! in reply to Bob, 02-18-2002 11:49:52  
Check your fuel flow. My 50 had same problem. Took sediment bowl off and removed strainers only to find heavy corrossion which was preventing adequate fuel flow under load. Something worth checking anyway!



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Bob

02-18-2002 16:09:59




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 Re: Re: JD-50 HELP! in reply to Guy, 02-18-2002 12:41:24  
I'm a little embarassed that I didn't check this before!!! I did check it this afternoon and both the sediment bowl and the strainer in the carb were clean. Thanks!



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JACK

02-19-2002 17:48:58




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 Re: Re: Re: JD-50 HELP! in reply to Bob, 02-18-2002 16:09:59  
Did you check for a restriction in the exhaust system?. Slight possiblity that it is it, but an engine must be able to breath correctly to run right. if air can get in and not out, it will act like this.



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Bob

02-21-2002 13:52:09




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 Re: Re: Re: Re: JD-50 HELP! in reply to JACK, 02-19-2002 17:48:58  
You were correct about the restriction! Turns out the exhaust valve got turned about 15 - 20 degrees and was enough to cause the restriction. The 50 rune great now! Thanks much for your input!



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