1947 JD A rough running at open throttle

CharlesTx · Oct 1, 2014

My 1947 A is running rough with the throttle open. At low to mid range it seems to run good. I tried pulling a plow and found the tractor lacks power and is exhausting black smoke with the throttle open, it also pops back through the oil bath air cleaner. This tractor ran great until today. Could this be a carb issue or more likely a stopped up air cleaner?

Kemper · Oct 1, 2014

I would turn the load screw on the carb in about a quarter of a turn and try it

Juicybusa2 · Oct 1, 2014

And a fresh set of plugs.

BushogPapa · Oct 1, 2014

Have you checked for moisture inside the Dist/Mag Cover..?
There also could be "Carbon Tracks" inside the Dist/Mag cover that would promote errant Spark.
Are the Plug Wires in "as NEW" condition.?
To be sure the Inlet pipe to the Air Cleaner is not restricted by dirt or Mud Dauber nests, take the oil cup off the Air Cleaner and see if that makes any difference (removing it bypasses the Air Filter and upper air inlet pipe)..

Ron.

Lee B · Oct 2, 2014

It shouldn't be popping back thru the air cleaner unless an intake valve is sticking. Power stroke is a very long 70 degrees after the intake should be closed completely, any fire in the intake side means that valve isn't closed or is wildly out of adjustment and not closing because of that issue. I would just go in there to adjust the valves and while there verify that both exhaust rockers are getting oil which then splashes onto the intakes to oil them. If the oil delivery tube is plugged on one side then that intake is dry as bone and might be sticking just enough at fast speed to let fire past it on occasion. The rest of the time it might be sticking only enough to foul up the mixture for both sides which is where the black smoke is coming from. With sudden onset, it all seems to fit the symptoms, only reason I like it and offer it here as a possible. Really could be any of the offerings given below. I'm in classic view, maybe that should be above in modern view?

RandyB(MI) · Oct 2, 2014

Could be any of the things listed below but I will add that if , in fact, it IS actually backfiring through the carb/air filter AND it just started doing it and does it consistantly than the one thing not mentioned would be a broken valve spring. First thing I would do though , is start at the sediment bowl and work your way down to make sure you have plenty of fuel flow.They have a way of plugging in the fitting right above the sediment bulb assy. If it ran perfectly before than you shouldn't need to adjust needles but doing so and noticing change for the better would be indicative of blockage internally in carb galleries. You didn't say what happens if you choke it and you also didn't indicate what you mean by wide open throttle. Wide open throttle LEVER and wide open throttle PLATE are two completely different things. The first is called "fast idle" and throttle plate is barely open. true WOT will only come with a plow or heavy load on it. Let us know what you find.

Pete in MD · Oct 2, 2014

Ron,
Removing the oil cup doesn't bypass the air cleaner.

BushogPapa · Oct 4, 2014

I suppose technically it does not, BUT it DOES eliminate the upper air Inlet Tube, which can be badly restricted and a common location of Inlet problems..
Caked Dust and/or Mud Dauber nests can accumulate and block the upper inlet at the "Dog-Leg" above the air filter unit.

I use a flexible garden Hose (with NO end-fitting) from the bottom of the air filter canister, up the center Tube, all the way to the Top of the Upper Inlet Stack and allow water to flush until it runs clean water.
Surprising how much dirt, etc will flush out..

Ron.

Pete in MD · Oct 4, 2014

I agree with you Ron on the upper air inlet pipe, both the problems and the solution.

1947 JD A rough running at open throttle

CharlesTx

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Kemper

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Juicybusa2

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BushogPapa

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Lee B

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RandyB(MI)

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Pete in MD

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BushogPapa

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Pete in MD

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