John Deere MT

Gene Davis · Oct 1, 2008

I have a 1952 JD MT that ahs been been converted to 12 volt prior to our acquistion. I don't know if this tractor is supposed to be a Positive ground and that we have wried correctly. We have installed a 12 volt coil and condensered without a resistor. It is hard to start and seems to struggle to run. Any suggestions would be apprecaited.

Bob · Oct 1, 2008

Since it's converted to 12 Volts, you might as well make it (-) ground. (Must be a generator, rather than an alternator if you have the choice to go with either polarity?)

Connect the coil's (-) terminal to the distributor.

NOT sure what you mean by a "12-Volt condensor", as 'most all ignition condensers are rated in the 300 to 600 Volt range.

Did you install a REAL "needs NO external resistor" 12-Volt coil? Got a part #?

Is the timing correct?

John T · Oct 1, 2008

Well, it was originally Positive ground but no telling what it is after the changeover. Look n see if the batterys + or - is tied to frame, theres your answer. If it used an alternator most all are Negative ground. It originally had a 6 volt coil but at the now 12 volts you need a full true 12 volt coil NO BALLAST USED.

The coil needs to match polarity i.e. if at Neg ground its lil + terminal gets voltage from the ignition switch while its other lil - wires to distributor,,,,,,,if at Pos ground the - wires to switch and + wires to distributor.

It needs good plugs, good points n condensor, and timed correct, after that it takes good compression and correct carburetion

John T

Gene Davis · Oct 1, 2008

Have to check and let you know.

But, what"s the deal either way?

In otherwords, if it has a resisitor what the correct way of wiring or if it doesn"t?

Gene Davis (Ga.) · Oct 1, 2008

I worked for local Deere dealership when the M series debuted. The M series from John Deeres always ran lazy,like they were a few degrees late with their timing. It is the nature of the beast. This series of tractors was the first of the Dubuque works offering to the farmer. This tractor was not anywhere as good as it's descendants,the 40 series and the 420 & 430 tractors. They also had some of the meanest implements to attach to the rear of the tractor with that long coupling pole. The rubber bladder of the seat had a nasty habit of blowing out and the telescoping steering wheel shaft was a boondoggle for sure. This said,have you checked the timing with a light? The distributor bushings and the advance mechanisim will both cause timing and dwell problems that contribute to poor running. Does it run on both cylinders? These tractors have to have the oil pump timed or they will run only on one cylinder. These tractors were notorious for having problems with the starter not getting a good ground connection. the ground strap needs to be hooked to the end bolt of the starter housing.

Gene Davis · Oct 3, 2008

I sure appreciate the information.

I have checked the play in the distributor shaft and there is a little,side to side, but not much.

The problem is that when you start the tractor, it runs really rough and pops and sputters, acts likes itis missing on oned cylinder sometimes. When you pull the choke out, it trysto run better.

We have overhauled the carb and soaked overnite replacedthe floats,needle valve etc. The only thing left, is the air adjustment screw broke off when we tried to turn. After all else, we finally drilled this out and re-tapped. I am in the process of trying to get a new one. Do you think this might be our problem?

What else might you suggest?

Thanks.

Glen D Anderson · Oct 3, 2008

Still having trouble with the old girl?

I remember you posted a while ago.............

Have you tested the compression yet? There's no sense trying to make a silk purse if you've got 40 psi. on one cylinder and 110 psi. on the other..............this would be first and foremost

Secondly, confirming timing as the "other" Gene suggests would be the next step.............make sure the firing order is right first.........I know there's only two wires BUT the engine WILL run with the wires swapped, confirm dynamic timing with an actual timing light..........

Lastly, by the indications you gave it sounds like a lean condition if choking it causes it to run better, so getting the idle and load circuit adjustments working properly on your carburetor would be the first thing to contend with........also in this "drilling and re-tapping" process filings may have found their way into some of the passages in the carb.......are you SURE ALL of the passages are clear??

Good luck,

Glen

Gene Davis · Oct 3, 2008

Glen,

Thanks for all your help.

I hate to sound stupid, but if you are looking at the tractor, I know that the firing order is 1 and 2. How should the wiring be attached to the distributor cap?

To answer your question about compression,no, I haven't check this yet. I will have to borrow a compression tester in order to check and I will do so.

Glen D Anderson · Oct 3, 2008

Sorry, I dont have the manual or our 40U in front of me right now so I can't answer your question............

Post this in the John Deere section and fellows like Mike M or d. coleman will likely have that answer off the top of their heads.............

Gene Davis · Oct 3, 2008

Thanks.

I can take a look at the direction with the cap off and tell.

I know how I have it wired up and I think it may be right.

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