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My MTD 115/76 with a Tecumseh Formula 12.5HP Engine was working ok but then will no longer start. I have changed the inline fuel filter & fuel ssems to be getting to the carburettor ok, but there is no sign of wetting on the spark plug. Reading comments there seems to be an issue with this type of carburettor involving a solenoid. I cannot seem to find any specific information on these carburettors. Should I look to replace it or is there a better alternative to fit? Any help would be much appreciated. Terry

That carb needs a lot of TLC. I’m guessing good cleaning and rebuild is needed. Including replacing the float needle and seat, plus resetting the float height. This site may be of some help. If you need to post back, make sure you include all Tecumseh model and spec numbers.

Many thanks, the information on the engine is shown in the picture, hope that helps.

Poor picture, can’t read the numbers.

Hi, I posted before on the problem I am having with my MTD 115/76 Ride on Mower. It has a 12.5HP tecumseh engine (model number shown in the picture. I thought at first the problem may have been the fuel, so replaced the inline fuel filter, carburettor etc., But it appears the problem is electrical. I couldn't get any sign of a spark, so replaced the coil & spark plug but still no joy. Even removing the kill switch wire doesn't make any difference. Any help on troubleshooting would be much appreciated. Thanks, Terry

Here is the model details.

If you have no spark with the kill wire removed, check these there things.
1. Coil mounted upside down.
2. Wrong coil air gap, should be be .010”
3. Wrong coil, should be Tecumseh part number 36344A.
if not one of these three, bad coil.

Thanks for that. I am still at a loss as I have run through all your suggestions and bought a brand new compatible coil 36344A, but still no spark. What else shoild I check? Thanks, Terry

If you have the coil is mounted correctly and gapped at 010” and the only thing connected to the coil is the spark plug you should have spark. No spark, I say you have a bad coil, even it is new. Hope you bought from a good dealer, as most will not warranty electrical parts once they walk out the door.

Understood. Is there a way I can test the coil? Really appreciate your help. Thanks, Terry

You just tested it the way 95% of the techs on this sire do it.

You sdid. I couldn't get any sign of a spark, so replaced the coil & spark plug but still no joy. Even removing the kill switch wire doesn't make any difference. Terry. There is no other way to test the ign module. Once you disconnect the kill wire and spin the engine over and check it with a spark tester and get no fire you have a bad coil. They either work or they don't work.

Out of curiosity can the coil be put on the other way round ?
The hall effect chip is polarity sensitive so the voltage generated in the coil generated has to be negative 0 then positive if it is + 0 - then you will get no spark
The only other thing is a bad magnet in the flywheel . very rare for this to happen .

Hi, thanks. I tried flipping the coil and still no spark. I think the magnet on the flwheel is ok as it grabs the coil when fitting & is difficult to prise apart to set the air gap. Thanks, Terry

Hi, I have tried flipping it but still no spark. I think the flywheel magnet is ok, as when I fit the coil it grabs the magnet hard against the flywheel, making it difficult to separate. Thanks, Terry

JBASport said:

Hi, thanks. I tried flipping the coil and still no spark. I think the magnet on the flwheel is ok as it grabs the coil when fitting & is difficult to prise apart to set the air gap. Thanks, Terry

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I have bought 2 new coils (from different suppliers) and still cannot get a spark! Both were matched against the engine type/serial number. The magnets on the flwheel seem to be strong, as when I fit the new coils the magnetism grabs the coil against the magnets on the flyweel and makes it difficult to set the air gap. Not knowing how strong the magnets should be, is it possible to increase the strength of magnets by rubbing a stronger magnet against the ones on the flywheel? Other than that I am at a loss as to what to do next to get a spark! Thanks, Terry

The only way I know to test the coil is to test for spark. Use a spark tester, or remove the plug, connect the plug wire, and ground the plug. Don't hold the plug in your hand, or you can get shocked. Have someone else pull the cord, and watch for spark. There may be a test with a good voltmeter, but I don't know about it.

Thanks Mark

Mark H_NO said:

The only way I know to test the coil is to test for spark. Use a spark tester, or remove the plug, connect the plug wire, and ground the plug. Don't hold the plug in your hand, or you can get shocked. Have someone else pull the cord, and watch for spark. There may be a test with a good voltmeter, but I don't know about it.

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Fuel, compression, spark, and timing are what you need to run. If you're doing this to check spark, it may be a good idea to check the flywheel key. It can be sheared by suddenly stopping the blade(hitting a big root hard.) Take the nut and washer off the flywheel, it's pretty easy to see it's sheared. Here's an example.

Mark H_NO said:

Fuel, compression, spark, and timing are what you need to run. If you're doing this to check spark, it may be a good idea to check the flywheel key. It can be sheared by suddenly stopping the blade(hitting a big root hard.) Take the nut and washer off the flywheel, it's pretty easy to see it's sheared. Here's an example.View attachment 69090

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Thanks for that, will check that out & have also ordered an OEM coil just to be sure. Terry

Make sure you don't get lube on the flywheel or shaft if you pull it, that can cause the key to be sheared.

Thank

Mark H_NO said:

Make sure you don't get lube on the flywheel or shaft if you pull it, that can cause the key to be sheared.

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Thanks for the tip.