Need help with Fairbanks Morse magneto

blue_tractor_man · Nov 17, 2018

Back on the non-tractor Kohler generator. Engine is torn down with no head or valves. The starter is spinning the motor very fast. Maybe 600 -1000 RPM, just guessing. It is a Type 20 impulse magneto. OK, I get a nice blue spark while the impulse is clicking, but when the RPMs get above what makes the impulse click the spark becomes infrequent or not at all. I have one of those little spark tester gadgets set at 1/4 inch or better. I tested the condenser with my Fluke meter, and it showed .3 microfarads. What should I check next?src="https://www.yesterdaystractors.com/cvphotos/cvphoto2990.jpg">

guido · Nov 17, 2018

Hello bluetractorman,

One of the causes of intermittent spark is dirty contacts. Close gap, 25% or more will give the same results. Weak magnito magnets is another. Spark plug lead wire at the coil and with corrosion built up is another. I am betting on the points,

Guido.

LarrySTN · Nov 17, 2018

Try increasing your point gap to see if it improves your spark. The recommended point gap doesn't always give the best spark. I have yet to see a magneto require less gap than recommended, but have often had to increase the gap to peak a magneto. If that doesn't help you may need the magnet charged, providing the coil is in excellent working condition.

blue_tractor_man · Nov 17, 2018

Guys, thanks for the replies. I forgot to say that I took the points out and polished them with some 600 grit sandpaper, reinstalled them, gapped them at .015, then wiped them clean with some writing paper.

Waterloo · Nov 18, 2018

Most likely the magnets are weak. Start by replacing the condenser just to make sure. The coil could be weak and can be replaced second. If the impulse is working; the points, condenser and coil are good the only item remaining is the magnets. This is the approach I would take. To recharge the magnets (requires a magnet recharging machine)the magneto must be totally disassembled. The prior items can be replaced basically with the removal of the cap.

teddy52food · Nov 18, 2018

If it gives a good hot spark at impulse, the magnets are not weak. In other words, there is nothing wrong with it. It may be a little weak at the RPM just above impulse but when the engine starts it will jump over that RPM & run just fine.

Need help with Fairbanks Morse magneto

blue_tractor_man

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guido

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LarrySTN

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blue_tractor_man

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Waterloo

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teddy52food

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