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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 28058
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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Craftsman mower model number 917.256531 with B&S 15.5 HP.

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Craftsman mower model numberNNN-NN-NNNNwith B&S 15.5 HP. I replaced the ring gear with replacement gear and reassembled. I wasn't sure of gap for magneto armature to the rotating magneto, so gapped as close as possible without binding magneto rotation. Mower will crank with starter but will not "fire" off, it just cranks and cranks. I have checked the spark plug - cleaned and gapped. It has new gas, I've blown out the gas line and filter. The mower ran fine before I did the ring gear replacement. Looking for help on how to get the mower running.
Magneto should be gapped at .010in. Check the small wire on the magneto to be sure it is not grounded out, it is the kill wire, and if it is grounded, you will have no spark. Remove the wire from the magneto and check for spark. Also you didn't mount the magneto upside down did you?
Customer: replied 6 years ago.

Okay, I gapped the armeture has suggested. The correct side is up. Removed small wire. Tried to start, it just cranks and cranks with no indication of "firing". I also checked the connector that was in the wiring circuit. Checked small wire found no issues. Next?

Have you actually pulled the plug and with it grounded see if you have spark? You might have spark, but no fuel. Check the electric fuel shutoff valve in the base of the carburetor, it has to open(click) for the fuel to enter the engine. It has to have battery voltage to it when the key is turn on.
Customer: replied 6 years ago.

Tryng the suggestions...the spark plug broke...won't be able to get one until tomorrow after work. I couldn't tell if the click sound to the electrcic shutoff valve occurred or not... I have no help to allow me to get closer to the solenoid while trying the ignition.

I will not assume that there was already a crack in the spark plug as I had not looked for that, yet there was nothing obvious when I cleaned and gapped it. So I am on hold until tomorrow.

I will check back.
Customer: replied 6 years ago.

Okay, I have changed the spark plug with a new one. I went ahead and replaced the armeture since they had one in stock. Engine still just cranks and cranks no fire.

So I have ordered a new wiring harness for the electric shutoff valve and kill switch. I ordered a new fuel gas solenoid. After I replace all this if the engine still does not fire...what are my next 3 steps or so to check. I beleive that all the plunger type permissive switches are working.

!!! After you changed the plug and the armature(coil)? did you have spark? All you have to do to check the electric fuel shutoff is remove it from the carb. and turn on the key! If you have spark, and the solenoid is opening the fuel, and the timing is correct,??? Did you put the key back in the flywheel to crankshaft when you replaced the flywheel??
Customer: replied 6 years ago.

I put the new key in the flywheel to the crankshaft.

How can I check the timing?

I did not check spark yet. Not sure how to ground for the test. Do I have to crank it or just turn on the ignition key? I am by myself and not sure how to manage the distance with having to push in clutch, sit on the seat, etc....

I am on hold until tomorrow after work. Still won't have the other parts, but maybe can check spark, etc...

Timing is right if you put the key in place. To check the spark, you can use a piece of wire wrapped around the spark plug base to ground it on the block or anything else metal., and you will have to crank the engine to see if you have spark. Position it so you can see the plug when you crank it.
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