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Have a model 917.258523 with a 15.5 Briggs. It started out not turning over with the key but I could jump the solenoid. I found that I had 2 safety switches that was not working so I bypassed them. Now it turns over with the key but won't fire when turning but when I let up on the key it starts to fire till the motor stops turning. I have never had anything like this happen before. Please help

I would say either wrong or faulty key switch. Assuming you have a fuel shutoff solenoid on the carb. It isn't getting power in the start position on the key switch.

When you bypassed the safety switches, you also inadvertently bypassed the ignition circuit. Not sure on your unit but most have a seat switch designed to kill the unit if the operator steps off the unit while running. Also other safety functions will apply. All I can offer without a circuit diagram. Guys?

lzn197 said:

When you bypassed the safety switches, you also inadvertently bypassed the ignition circuit. Not sure on your unit but most have a seat switch designed to kill the unit if the operator steps off the unit while running. Also other safety functions will apply. All I can offer without a circuit diagram. Guys?

Click to expand...

Yep, and bypassed the fuel shut off solenoid.

http://www.searspartsdirect.com/par...10057284/00001?blt=06&prst=0&shdMod=917258523


Check 30 amp fuse and see if it is blown, item 26 on parts breakdown. If fuse is good, check all electrical connections for corrosion, rust, and make sure all connections are tight. If fuses keep blowing, use multi-meter tool to check all safety switches as well as ignition switch,etc.

I have seen this before. Diode in wiring harness some where is bad. Most of the time it will be in the loom under electrical tape, so its a big job looking for it. Some MTD units are near the engine but it will be in the tractors harness, not the engine. If you do find it, meter it to check to see if bad. You can get one a Radio Shack other than that, new harness.

Deerlane said:

I have seen this before. Diode in wiring harness some where is bad. Most of the time it will be in the loom under electrical tape, so its a big job looking for it. Some MTD units are near the engine but it will be in the tractors harness, not the engine. If you do find it, meter it to check to see if bad. You can get one a Radio Shack other than that, new harness.

Click to expand...

Yep if you are not careful jumping a mower off it will fry that diode then it wont retain charge from the alternator/ stator.

mechanic mark said:

http://www.searspartsdirect.com/par...10057284/00001?blt=06&prst=0&shdMod=917258523


Check 30 amp fuse and see if it is blown, item 26 on parts breakdown. If fuse is good, check all electrical connections for corrosion, rust, and make sure all connections are tight. If fuses keep blowing, use multi-meter tool to check all safety switches as well as ignition switch,etc.

Click to expand...

https://www.google.com/search?q=wir...4AovQsQSfooDQAw&ved=0CDIQsAQ&biw=1280&bih=675