1947 D Carb adjustments and ideas for backfire

Schultz · Apr 10, 2014

I'm not familiar with the JD line but a friend inherited a 47D and when it warms up it randomly backfires out the right stack. The stack is not hot to the touch like the left side so I'm thinking it's not firing, but why? Fuel/Spark? I figured I'd start with plugs/wires and then start going from there. Does anyone have any suggestions on this? I figure the last thing on the list was valve lash. Is this easy to do / get to on these?

Thanks for all the help
Brent

John Deere D · Apr 10, 2014

Start by swapping the spark plugs and verify if the problem changes to the other cylinder. Remove the distributor cap and make sure contacts inside cap are clean and shinny. Make sure rotor is firm on mag armature (not loose)and all metal parts of rotor are shinny. Make sure there is no moisture inside Mag Cap. If you have access to a multi meter check each spark plug wire for resistance (ohms). Spark plug wires should have a metal conducting core NOT CARBON if your D has a Magneto. Make sure the seat (point where the spark plug bottoms out on the head) are clean and shinny. When you purchase new Spark Plugs be sure to purchase plugs with NO resistor. Check to see that the two outlets on the Mag Cap where the spark plug wire plugs into are clean and shinny. Usually the top spark plug wire on the Mag runs to the left cylinder Spark plug, and the bottom spark plug wire runs to the right cylinder spark plug. Right and left are viewed as if you are on the tractor operating it from the drivers seat.

gtx1967jewison · Apr 10, 2014

If not an ignition issue, then it's just lean.

Earl-IL · Apr 10, 2014

What mag is on this tractor ?

Mike M · Apr 10, 2014

A 2 cyl Deere with a single induction carb. will not always fire on both cylinders unless it is under a load. The right hand cyl. is the weak side.
Having a dual stack set up on a D could possibly make them backfire at times worse then normal ? I never had one with that set up.

Schultz · Apr 10, 2014

That I do not know, I'll have to take a look and get a picture.

JRSutton · Apr 10, 2014

A carb out of adjustment can do it. Checking it is very quick and simple.

I'm pretty sure the carb on the D has two needle adjustments you can do by hand - a load needle and an idle needle. (should be marked on the carb - look closely).

Open the idle needle up a few clicks and see if it makes a difference. If not, go a little more. If you're blowing black smoke, you've gone too far And if it's still backfiring, put it back where it was and look elsewhere.

(if you get lost on where you're at with it, just crank it all the way in, then back out 1 1/2 turns and it should be good).

If you're still backfiring - I'd look at the plugs, and while they're out do a compression check on each cylinder.

1947 D Carb adjustments and ideas for backfire

Schultz

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John Deere D

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gtx1967jewison

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Earl-IL

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Mike M

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Schultz

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JRSutton

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