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Discussion Starter · #1 ·
My tractor has the 18.5 Briggs
It will spin, but will not fire

Here is what I have done so far...

1. replaced spark plug twice just to be sure
2. cleaned carb twice
3. checked gas flow, no problem
4. jumped safety switch under the seat
5. removed wire from magneto
6. tried to check spark plug wire for fire against motor but the cap may be
too long...
7. lots of profanity
magneto would be easy to replace, just wanted to eliminate other possibilities before I did that, high school shop teacher says of all the mowers his students rebuild, magneto has never been problem.....but this is me

Thanx for any insights.....
 

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I sure hope you did not shear the fly wheel key, might check that if all else fails.
 

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Put some gas right in the carb throat and try to start it, if it fires then stops its fuel related, if not its probably ignition or timing.
 

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6. tried to check spark plug wire for fire against motor but the cap may be
too long...

I take it you tried just the end of the wire, not with the plug in it? If so put the plug in the wire and ground the plug. Just MAKE SURE you are not touching the plug electrode or you will go :swow: if its firing. Be safe and wear a leather glove, although I have been bit through a glove but not as bad as getting zapped on my bare hand. :eek:mg: that hurts!
 

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A sheared flywheel key will only throw it out of time if it still spins the engine, but its always worth a look
 

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You should supply the sears 917.xxxxxx number.
Different era tractors can have different schematics.
In some cases, unplugging or jumping the seat switch will result in no spark. In other cases...... who knows?
 

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6. tried to check spark plug wire for fire against motor but the cap may be
too long...

I take it you tried just the end of the wire, not with the plug in it? If so put the plug in the wire and ground the plug. Just MAKE SURE you are not touching the plug electrode or you will go :swow: if its firing. Be safe and wear a leather glove, although I have been bit through a glove but not as bad as getting zapped on my bare hand. :eek:mg: that hurts!
With the shroud off the motor plug the spark plug in and lay it in between two of the fins on the motor, it should rest nicely in there and that way you wont get zapped when testing for spark. With the ground wire off of the magneto you should get spark regardless of the safety switches, if you don't get spark check that the magneto is gapped properly. If you have spark try pouring a little gas down the carb like gmaster said. If it fires when you do that its fuel related.
 

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Discussion Starter · #11 ·
no fire and the key is okay, either something in the safety switching or the coil, gonna check with local repairman and see if he has used one, if it works I will get a new one...
 

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Take the shroud off and take the wire off the coil and put the spark plug against the block, turn it over, it should have spark no matter what. If not its a bad coil. Ps, dont try this with the plug in the engine becouse if it works you will have to pull the wire of to kill the engine.
 

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Take the shroud off and take the wire off the coil and put the spark plug against the block, turn it over, it should have spark no matter what. If not its a bad coil. Ps, dont try this with the plug in the engine becouse if it works you will have to pull the wire of to kill the engine.
:ditto:

Find out before you spend any money you don't have to...

He's referring to the mag grounding wire, just to clarify.
 

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Don't know which engine you have but this week I have had 2 pressure washers in that did not have spark. 16hp Briggs vanguard's. The culprit, one or both the diodes in the mag ground wires were defective. Went to radio Shack and got 2 diodes for less than $3.00 and made my own kill wires, you just have to know which direction to solder them in. How to test a diode? Remove the wires from the mag and shroud terminal. Get a continuity tester, the kind with a battery and light bulb in it. Clip one probe to one end of the wire, the other probe to the other end. Note light or no light condition. Now switch the probes around and note light or no light. If you get a light in both directions, bad diode. No light in either direction, bad diode. Light in only one direction good diode. Be sure to check both diodes (assuming you have a twin cylinder). If you are on a twin and only one diode is bad, it will kill that mag and only run on one cylinder. Same test works for the B&S charging diode.
 
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