741 coil replacement

goosefoot farm · Mar 2, 2017

I recently converted my 741 to 12 volt, and the 6V coil might be going out. If I do need a new coil, is there any reason to get another 6V one? If I get a 12V one, what should be the resistances?

rvirgil_KS · Mar 2, 2017

6 volt coil (1 1/2 ohm primary) with 12 volts would require a resistor. Direct 12 volt coil (3 ohm primary) would not require a resistor.

I would get a direct 12 volt. NAPA IC14SB or equivalent

goosefoot farm · Mar 3, 2017

Thanks for the info. I was working on it today and could get a spark plug to make sparks when trying to start, but they seem weak. The tractor has been difficult to start since I bought it last summer, which is one reason why I upgraded to 12V. Could I put a bypass on the external coil resistor that gets activated when the starter button is pressed? Would that make a stronger spark when starting? Would that be bad for the coil?

Royse · Mar 3, 2017

"The tractor has been difficult to start since I bought it"

Are you sure someone didn't already put a 12V coil on it?
Usually they're marked on the outside of the can.

If it says something to the effect of "12V for use with an
external resistor" then it's not a true 12V coil but if it says
something more along the lines of "12V no external resistor
required", then you shouldn't have one.

The coils are usually pretty reliable though.
Points, not so much. They corrode from lack of use
Have you cleaned and gapped the points?

souNdguy · Mar 3, 2017

Your description I the opposite of what an ignition bypass resistor should be doing. If you have a 6v coil and resistor on 12v, you can wire it so that resistor is in series when running, but bypassed at start.

Me? I'd run new wires, he new switch, Napa ic14sb coil, no resistor, and cleaned, gapped, good points, with clean gapped plugs, and a cleaned , dry, untracked dizzy cap, and intact rotor on shaft securely with clip.

goosefoot farm · Mar 3, 2017

You're describing what I was trying to say and didn't do well. There is not a bypass now, but I think I need to add one that activates when I press the starter button. All the wires are in good condition, I put new spark plugs in, cleaned and reset the points, checked the distributor cap and rotor, and it still doesn't start. When I did get it started before, it usually fired just as I was taking my finger off the starter button. After searching on the forum, that seems to be an issue of the starter motor hogging too much of the juice, hence why I want to try a bypass.
The coil is definitely 6V with the right resistances.

goosefoot farm · Mar 4, 2017

new coil fixed everything. sounds great now.

741 coil replacement

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