No Spark even with new magnetron - HELP!

[cuengineer]

I have a Snapper Model 281011BTE mower with a 10 hp B&S Model 254707 Type 0124-01 engine with magnetron ignition. It was running fine while cutting and unexpectedly just cut off - in middle of yard. I checked and no spark so first put a new plug in - still no spark. I then took off the cover and disconnected the shut off wire. Still no spark. I then figured it was the magnetron so I got a new one. I adjusted it to 0.010" gap between magnet on flywheel. I also cleaned the bottom of the magnetron and the engine to be sure it made a connection. Still no spark. I also checked the crankshaft key which seems fine, too. I finally got another new magnetron to check thinking the first might have been defective and still no spark. Any other ideas?

I was told by my local dealer than if there is no spark to the plug, it must be the magnetron but that there is no good way to check it without putting it on the engine. Engine turns over with no problem using electric starter. One issue I wondered about is that the part number for the magnetron has changed so I wonder if there might be a problem there. But the replacement number according to the book calls for the B&S like I got. Any help would be much appreciated.

 

[Fish]

Yeah, give all of the numbers off of the engine, "code" numbers....

Also give the coil's part numbers

The thing that destroys these ignitions is voltage getting sent to the small "kill" wire that is plugged into the base of the coil, so
If you plugged in a new good expensive coil, and it sent voltage to that one too, then you have destroyed the new one as well.

 

[cuengineer]

As mentioned in the OP, I disconnected the "kill" wire before installing the magnetron to make sure that it was not shorting the spark. Also, I checked with switch on and with starter turning and had no voltage on this wire. The engine's code is 92082710 and the replacement magnetron is a B&S 398811.

The dealer said that this was a replacement for the original which is no longer available. It must be a somewhat generic one since the plug wire is over twice as long and the directions indicate how to cut it to correct length (which I have not done to this point). If I put a voltmeter on the spark wire, I do get a slight (0.06-0.08 volt) spike as I turn the flywheel/magnet pass the magnetron. The magnet seems to be pretty strong as far as I can tell, i.e., it squeezes the adjustment card tightly when adjusting the gap to the flywheel and has a very noticeable pull.

 

[Fish]

the engine setup in it's basic form, with the magneto ignition system....

Every revolution of the flywheel past the electronic ignition coil over a certain crank speed will produce a spark that will run the engine.

 

[Fish]

If the coil is good, and the spin of the flywheel is enough, you will have a spark. Provided the kill wire is disconnected or very less likely, the flywheel has lost it's magnetic charge......

 

[Fish]

Like I said earlier.... If at any time you hooked up the small "kill" wire to any new coil, you likely destroyed it then. Get a decent
voltmeter.

 

[Fish]

If you put on a new coil, leave the kill wire disconnected, but to shut it off, you will need to yank the plug wire!!!! But you will not destroy another ignition.....

 

[cuengineer]

What is frustrating is not being able to check the magnetron itself. As stated in the OP, "I then took off the cover and disconnected the shut off wire. Still no spark. I then figured it was the magnetron so I got a new one." I have not reconnected the "kill/shutoff" wire, but I have no idea whether someone might have tried this on a mower that was getting power to the kill connection and returned it to the dealer before I got it.

Not sure what your comment about getting a "good" voltmeter since I think mine is a "good" one. Plus I have checked the circuits with more than one anyway and they ALL get the same response. Thanks anyway. Back to ballgame!

 

[Fish]

Well sorry about the voltmeter slur.... At any way at all!!! If you have an engine with a good flywheel, and you bolt on a "good coil", and do not hook up the small "kill" wire, and crank the engine you will generate a spark!!!!!

 

[Fish]

If not, then the new coil is bad, or the flywheel is bad [lost magnets], but I have never ever seen that!