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John Deere Tractors Discussion Forum

JD50B no start

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Joel Markwat

11-22-2003 19:27:26

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My 1950 B, which was restored about 10 years ago has been setting for a while. I start it and run it ocassionally but now it won't start. It has a magneto. I've cleaned the carb, checked timing and spark. The spark is what I'm questioning, it seems erratic and not strong enough.

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John T

11-23-2003 06:09:29

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 Re: JD50B no start in reply to Joel Markwat, 11-22-2003 19:27:26  
Joel, I pretty much agree with Ron there, the first thing I would do is check the ignition points to be sure they are gapped properly and then NOT gray oxide coated or burned, pitted, or carboned, and replace and gap if so. A fresh set of plugs, maybe Autolite 388, wouldnt hurt things, and those 2 things plus a good clean cap and rotor is what I would first try and see how she does. (ASSUMING SHE IS GETTIGN SUFFICIENT FRESH CLEAN WATER FREE GAS, SEE BELOW)


If you remove the plugs with their wires atatched and their sides against the tractor frame for a ground and crank her over, do BOTH produce a good visible blue and NOT a faint thin wimpy yellow spark??? If so, do the points thing above (if its a Wico C or XH Model, gapped at 0.015) and have new plugs and see what the spark looks like then. The mag should produce a good loud SNAP each 180 of flywheel rotation (when the plugs fire, if its NOT a gear reduction mag) and NOT a dull soft clunk. Until the mag snaps, the plugs cant fire at cranking speeds, so is it doing that?????

If shes NOT snapping over at crank speeds but would start and run if pull started, the mags rear spring wind and trip assembly may be gummed up and not working to wind and trip the spring. If so, a removal and clean and light lube and wd 40 etc. on the trip dogs and assembly might cure the problem. SHA HAS TO SNAP AT CRANK SPEEDS TO PRODUCE A SPARK.

The weak erratic spark you mentioned may also be moisture or cracks or carbon traces in the cap. Remove and clean and inspect it PLUS make sure the lil spring in the cap makes good contact with a clean coil side output button/terminal. Is it????? ????? The wires should be wire core and NOT carbon auto suppressor types. If the cap and contact spring and points are all good and she snaps loud, post back for more in depth troubleshooting. Corrosion on the rotor or coil core etc etc etc could be other problems. Does it have any external kill switch or kill wire??? Be sure they are not shorted and no points wires to the condensor or coil or kill switch are NOT freyed or shorted and any kill switch stud out the side is not shorted.

POST BACK THE MAKE AND MODEL OF THE MAG for more tips on troubleshooting a weak or erratic spark.


From long sitting, the rings and cylinders can drain off the oil and loose their seal and the compression and vacuum is low causing hard starting. If you remove the plugs and squirt some oil into the cylinders and crank her over to move the oil around and she starts then, you may have ring and cylinder wear. A compresssion check can diagnose that or if she blue smokes a lot out the stack and has excessive crankcase blow by, those are also signs of wear.

If she has a good spark and decent compression but is hard to start, be sure the choke is working and shes gettign plenty of fuel.

Remove the air inlet and make sure the choke butterfly plate is tight on its shaft and is closing fully and staying closed or opens relative to where the choke is set externally.

Open the carb bowls lower drain cock/plug and with the gas on at the sediemnt bowl or any shut off, make sure a stream of gas around 1/16 inch flows steady and continuous a couple minutes. if not, check for clogs in the sediment bowl or inlet pipe and any 3 way valve is set right and working properly.

Have you adjusted the carbs top needles to see if it helps??? Initial rough in settings are 3/4 to 1 out for load and 1 3/4 to 2 out for idle.

You may want to remove the air cleaner bowl to see if its clean and has NO water in it while yuore at it.

Theres lots more, but lets see if its a spark orrrrr rrr a fuel starving orrrrr rrrr a low compression problem before posting all those troubleshooting tips.


Check the plugs spark, the mags snap, the points, wires and cap n rotor, then insure good fuel to thE carb, check the chokes operation AND YOU GOTTA HAVE FRESH CLEAN WATER FREE GAS.

Post back those findings and try to isolate a fuel or ignition problem or low compresion (try the oil in cylinders trick, look for blow by or blue smoke) and we will go from there.

Do the plugs appear flat black sooty powdery coated (excess unburned fuel, weak spark or carb too rich) or a wet uneven shiny black gunk coat (maybe oil burner).

Hope this helps get her going and answers your question, Post back you findings or e mail jmn50@msn.com any question and we will go further if needed.

Good Luck n God Bless ya Joel

John T

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Joel M.

11-24-2003 18:50:46

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 Re: Re: JD50B no start in reply to John T, 11-23-2003 06:09:29  
Thanks John and Ron for your replies. Here is some more info for you.
I did adjust the points the other day, but I'm not sure about their condition. The cap is clean but I'll have to take another look at the spring inside. Actually the coandition of the rotor bothers me a little, it seems loose on the shaft. The mag is a WICO Model X, Spec #XH1042, SER # XC118117. I had it off to check the timing and found the drive retaining nut had backed off. I took it apart, cleaned it and reassbled it (backwards first, experience is a good teacher) and then reinstalled. It has a good snap and will produce a spark, even by han, but seems to get weaker and erratic the longer I crank.
I just had the tractor running about a week before she wouldn't start for me, so I don't think it it a compression problem. I've had the bowl off the air cleaner,ok, and had the carb off, did a quick cleaning job. Their is good, new fuel to the carb. And the plugs are wet and flat black.
I'll have to leave her alone over the holiday, taking a raod trip but I'll get back to you as soon as possible.

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11-22-2003 21:53:19

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 Re: JD50B no start in reply to Joel Markwat, 11-22-2003 19:27:26  
Check the points in the Mag, to be sure they are not corroded...they should be bright and clean... Make SURE the mag does not have any moisture at all, in the back side of the cap... I have a friend who has a perfectly good 620, and it tends to have negligible compression and won't start until he sprays WD-40 into the cylinders, before he trys to start it in the spring.. Mechanic said it helps wet, and seal the rings that have been setting all winter.. New Plugs, set to about .025 would help it start if the spark is a little weak... Good Luck...!! Ron...

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