JD 70 gas All new ignition Cuts out above idle

ah724tractor · Jan 21, 2018

My JD 70 gas didn't like to start. Decided to freshen things up and replaced the entire ignition system: plugs, wires, coil, cap, rotor, points, condensor. Set static timing to about 10 ATDC.

For the first time ever, it starts immediately with the choke full on. Idles perfectly. But when I attempt to throttle up, the ignition starts cutting out as if the key switch was intermittently flipped off. Just before it dies, it fires again. Soon as it tries to rev up, it cuts out. Put my inductive timing light on left plug wire, and held the trigger. Flashes consistently at idle as expected. After revved up, the ignition goes out and usually doesn't resume unti the engine RPM is faded down to idle.

Any thoughts?

Thank you

ah724tractor

Duner Wi · Jan 21, 2018

My guess is condenser.

coonie minnie · Jan 21, 2018

It ran well before the ignition tune-up???

If not, I'd check your gas flow to the carbuerator. Not enough flow will cause the tractor to cut out at speed.

Russ from MN · Jan 21, 2018

We had a GMC truck act exactly like that, it was a bad distributor cap, I wouldn't expect a new one to be bad, but anything
is possible. A short term fix is to spray the inside of the cap with WD40 and then wipe out the excess, that will displace
the moisture out of the cracks.

Andy Martin · Jan 21, 2018

(quoted from post at 17:12:57 01/21/18) It ran well before the ignition tune-up???

If not, I'd check your gas flow to the carbuerator. Not enough flow will cause the tractor to cut out at speed.

Lack of fuel will usually not cause a timing light to quit.

Andy Martin · Jan 21, 2018

Shouldn't be too bad if it's only missing on two cylinders.

A weak spring on the points can also cause them to float and cut out at higher speeds. I agree probably the condenser, however. Try the old one.

Bob · Jan 21, 2018

WHERE did you get the components? (Brand name of parts?)

WHY did you replace the coil?

Did you get the correct coil, IIRC, it's essentially a 6 Volt coil using a ballast resistor and a starting bypass.

Points set using the proper procedure, and to the correct gap?

David G · Jan 21, 2018

Is there a reason you set timing to 10 after?

MSD · Jan 21, 2018

Condenser. New ones are mostly junk. Try the old one if it worked before the tuneup.

Steve@Advance · Jan 21, 2018

Revisit the points.

Be sure all connections are tight, especially where the insulator block goes through the housing.

Defective points can do the same thing, loose rivets in the spring, binding pivot, high resistance across
the contacts. They may need cleaning even though new.

A bad condenser, loose condenser ground. Distributor clamp loose causing bad ground.

The new points and condensers are notorious for being bad out of the box.

ah724tractor · Jan 21, 2018

Thanks. I've had several responses, and the most promising are to swap the condenser, and if not, the cap, even though both are new. Plug gap is 30, point gap is 20 or a hair over. Difficult to get exact.
It seems it's got to be the condenser or the cap. There is no in between, as the timing light shows. With the lights off in the barn and it's running, the timing light is brightly flicking then gone, just as though I shut off the ignition key, engine coasts down, then bang, it comes back. Sometimes, the first bang is the detonation of the raw charge in the exhaust left by the previous miss.

Condensor, then cap. Simplest and cheapest, and on from there.

Thanks again.

fixerupper · Jan 21, 2018

Condenser! The new condenser was junk out of the box as some of the new ones are. A bad condenser will make it act like it is lean.

RandyB(MI) · Jan 21, 2018

I'm tending to agree with the condenser issue but if that doesn't do it then check for badly worn distributer bushings as it would let the shaft cock to one sode at more rpm and might be enough to either not let points close or not open them at higher rpm when shaft cocks either towards the rub block or away from it. Either would prevent spark.

Russ from MN · Jan 21, 2018

Just try the old ones, troubleshoot one part at a time.

casecollectorsc · Jan 21, 2018

Points are too far open. When the engine speeds up point bounce doesn't let them close and quits firing, upon slowdown it fires again.

used red MN · Jan 21, 2018

Ding ding ding for Coonie Minnie. I?m no Deere guy but will those two bangers idle on one cylinder? If so unplug one spark plug wire and let it spark to the block. Start it up and throttle up. If the spark continues to fire as it shuts down then it is a fuel issue.

WGM · Jan 21, 2018

I never could understand the logic behind parts swapping for no reason. Put the old parts back on and I'll bet your tractor will run like new.

James Howell · Jan 22, 2018

Reviewed the [b:654c4848f0]OPERATOR'S MANUAL OM-R2035R JOHN DEERE TRACTOR MODEL 70 SERIES[/b:654c4848f0] under the [b:654c4848f0]IGNITION SYSTEM[/b:654c4848f0] section under the [i:654c4848f0]INSTALLING AND TIMING DISTRIBUTOR ON GASOLINE TRACTOR[/i:654c4848f0] on pages 87 ? 88.

"[i:654c4848f0]Continue turning the flywheel slowly until the ?10? ATDC? mark, stamped on the flywheel rim, lines with the notches in the timing hole in the flywheel cover.[/i:654c4848f0]"

Hope this helps.

ah724tractor · Jan 22, 2018

All have helped. The minute I get time to get back to the barn, I will, and once fixed, I'll post again. I've got a lot more ideas to work with than I had yesterday.

James Howell · Jan 22, 2018

"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">will those two bangers idle on one cylinder?[/i:654c4848f0][/b:654c4848f0]</font>"

Yes.

Reviewed the [b:654c4848f0]OPERATOR'S MANUAL OM-R2035R JOHN DEERE TRACTOR MODEL 70 SERIES[/b:654c4848f0] under the [i:654c4848f0]DUPLEX CARBURETOR[/i:654c4848f0] section under the [b:654c4848f0]Adjusting Duplex Carburetor[/b:654c4848f0] topic on pages 83.

Hope this helps.

James Howell · Jan 22, 2018

"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">If so unplug one spark plug wire and let it spark to the block.[/i:654c4848f0][/b:654c4848f0]</font>"

An in-line ignition spark tester can also be used.

Take a look at the photo below of the in-line ignition spark tester on "15" one of our 1953 Model 70 gas tractors.

ah724tractor · Jan 31, 2018

JD 70 running perfectly well now. Bought a coil for electronic ignition without realizing it, and it must over draw current on the points. Put original coil back in, but everything else is new. Cleaned carb. New gas. Starts and runs.

JD 70 gas All new ignition Cuts out above idle

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