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Discussion Starter #1 (Edited)
I have a Craftsman dyt 4000, model # 917.273621, 24ohv. When both spark plugs are hooked up it misses real bad. If i disconect the left plug, it idles fine. I have swapped the coils, replaced the plugs, always with the same result. Any help will be greatly appreciated
 

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go to sears, buy a cheap compression gauge, then follow directions on the packaging and check compression. This is something my 10 yr old son could do, so I'm sure you can do it also. It involves taking out the spark plugs and turning the key to start the engine.
 

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Well something you might try while waiting for a compression gage or whatever is disconnect both the kill wires from the base of BOTH coils and see what happens. Bare in mind that you will have to use some alternate method of stopping the engine if you do this.

Walt Conner
 

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Did you ever check to see if the flywheel key is sheared? That would be my number one check for mis-fires.

When you reinstall the flywheel, make sure the flywheel nut is tightened down nice and snug. If you don't have an impact wrench, make sure you use a block and mallet to give it a good snug and a >grunt<. :fing32:
 

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Id look for 2 things.

Bad diode in the kill harness.

Stuck valve/loose seat on the left cylinder.
 

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Hello Red, I was thinking about this post today mowing, as I have a similar engine, and couldn't for the life of me remember the purpose of the opposing diodes in the kill harness for the B&S V-twins.

What is their purpose?

Thanks,

Seth K. Pyle
 

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Hello Red, I was thinking about this post today mowing, as I have a similar engine, and couldn't for the life of me remember the purpose of the opposing diodes in the kill harness for the B&S V-twins.

What is their purpose?

Thanks,

Seth K. Pyle
Modern V-twins run 2 seperate coils,

The kill wire is hooked up to the secondary windings inside the coil itself. When the flywheel magnet passes by the armature, the flow of current runs through the secondary windings, then into the primary windings where it builds the power to make the spark..and it sent down the high tension lead to the plug.

Shorting the secondary windings to ground eliminates the spark just after its birth...every time a coil fires it is trying to send some current down the kill wire..but if it is just an open circuit it doesnt get anywhere and the only path is into the primary windings.

V-twins run a common kill wire (2 into 1). So if they spark 45* off of each other, when the first coil is activated it can send a little voltage to the other coil before it is ready to fire..and when the magnets pass the 2nd coil it can send a little voltage back to the first coil.

A diode is like a one ay valve...current can only flow one direction. On this application current is only allowed to flow OUT of the coil kill wire..so it can be grounded to kill the engine but current from the other coil cant prematurely activate that particular coil by corss feeding.

If one diode fails you may get intermittent sparks at the wrong time...way wrong time.

Ive seen both fail and it will just about blow the air filter and muffler off..
 

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Thanks Red, I knew there was an important reason relating to the separate coils, but could not remember.

Thanks again,

Seth K. Pyle
 
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