420 John Deere

ksujim · Jul 2, 2017

I have a 420 that coughs, sputters and barely runs.

We converted it to 12 volt. I sent the carb to a professional shop for a rebuild. New plugs, points, condenser. After sputtering awhile the intake manifold gets cold to the touch. (I understand the physics behind this.)

What am I missing?

You all helped me with a B and sucking oil out of the crankcase. Yes it was mud dobbers clogging the whole air intake.

Thanks in advance.

Steve@Advance · Jul 2, 2017

Look the points over closely, be sure they are making good contact. New points and condensers have a history of being bad out of the box.

Good, clean fuel?

How's the compression?

Valve train, sticking valve, broken valve spring, bent pushrod, valve lash?

bteny10 · Jul 2, 2017

Need help locating a john deere surflex disk or one way the newer style somebody has to know where to buy one an no I'm going to use it not part it out help if you can

Donald Lehman · Jul 3, 2017

Proper coil for 12 volt? Just because the points are new means nothing these days. I've heard others on here mention that sometimes you need a resister in the system?

John T · Jul 3, 2017

Goof morning Donald, FWIW its my opinion you correctly stated "I've heard others on here mention that sometimes you need a resister in the system?"

If you have a 12 volt car truck or tractor that uses a 6 volt coil THEN INDEED you need a series voltage dropping (12 to 6) ballast resistor between ignition switch and the 6 volt coils input so the coil receives its rated 6 volts NOT 12. Otherwise, the coil can overheat plus the points will burn prematurely. If its a 12 volt car truck or tractor and you don't use a ballast, then you need a full 12 volt rated coil very common and readily available from NAPA and a ton of other suppliers. Similar the coil needs to match polarity with the tractor be it POS Ground (as original on Deere two cylinders) or NEG ground as many were converted especially when alternators were used.

Best wishes God Bless and have a happy Fourth of July

John T

Nick m · Jul 4, 2017

My 430 did that when I bought it. Wasn't
running when I bought it. Was told it Was a
carb problem. Checked it over at home and
the points were whipped. New points burnt
fast. Put a resister on it and solved that
problem. It would still spit and sputter
once in a while then it'd magically clear
up. Ended up being the ignition switch.

ksujim · Jul 4, 2017

Where do you purchase a resister? Does anyone have a part number or example?

How was a bad ignition switch causing it to run poorly?

Nick m · Jul 5, 2017

The switch was letting the juice flow, but
not quite good enough. On the verge of
shutdown, but not quite there. Got my
resister at a local auto parts store.
Explained to them what I needed and they
knew.

buickanddeere · Jul 5, 2017

Use a 12V coil that has 3 or 4 ohms across the primary. Unless you want to use bypass starting.
There is no need however to convert a Dubuque to 12V to make it start better . If maintained and taken care of they will fire on the 2nd or 3rd turn at -20F factory stock.
M

420 John Deere

ksujim

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Steve@Advance

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bteny10

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Donald Lehman

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John T

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Nick m

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ksujim

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Nick m

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