Coil resistance values for 12v To-35

M77hawkeye · Oct 1, 2021

This message is a reply to an archived post by 257 Roberts on August 23, 2018 at 06:14:02.
The original subject was Coil resistance values for 12v To35.

Did that coil replacement fix your tractor
sputtering issues back in 2018?

I have a to 35 and it is doing the same
thing under load..runs for a bit then
sputters out.

Thanks

jvin248 · Oct 1, 2021

Sounds more like a fuel issue.

What is the coil resistance you have cold vs hot?

Did you clean up all the wire connections, verify no corrosion?

Bruce(OR) · Oct 2, 2021

I like coil specs.
I have found those are more useful when building a new coil and not so much once in service.
I have seen them fail well within spec and at .01 outside of spec.
Coil specs are good for a shot in the dark. I have gotten to the point of suspecting it bad to drop in another one.
I have also begun to see a lot of land of almost cheena ones being bad out of the box.
That makes diagnosis fun.

M77hawkeye · Oct 2, 2021

I have been the fuel and fuel line route..its not that.

An old timer tractor mechanic told me on the phone that when the coil and or points heat up and eirher or both older they can start to fail under load after tractor runs for a while.
The original post on this in 2018 talked about this and I wanted know if replacing the coil helped that 257 roberts post out.

Thoughts?

jvin248 · Oct 3, 2021

.

Temperature will certainly effect a coil.
Measure the ohms cold and measure again when it's hot enough you get your sputtering -- you might find the coil has a break in it that is opening when heated up if the coil is the source of the problem. Intermittent problems are difficult to solve.

How old is the condenser/capacitor inside the distributor? Capacitors are basically tinfoil and waxed paper rolled up and stuffed in a tube. They can break down over time and become ineffective, including temperature related.

If running it hot this way after dark can you see any arcing from worn plug wires? Cracked coil case or distributor cap? My one tractor came with a split distributor cap that would work but was sketchy.

What do the spark plugs look like when you pull them? Plugs can show symptoms from a range of issues. Keep track of which plug came from which cylinder and compare. You could have one or two cylinders with problems. Have you cleaned and gapped the plugs? Replaced them?

If you are really suspicious of the coil ... replacements are under $20 and if it's not the problem keep the old one for a spare.

.

Jerry/MT · Oct 6, 2021

Nominally a 12 v coil should have a resistance of 3.2 +/- ohms to limit the ignition current to ~ 4amps +/-.

Coil resistance values for 12v To-35

M77hawkeye

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M77hawkeye

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Jerry/MT

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