Murray 80/76 starting problems

[JHABT]

Hi there, I really hope someone can help me with this as it's driving me nuts!!
The Murray ride on mower is 20 years old and has always been reliable. This year it won't start. With the choke on, it fires up but doesn't keep running. I've been all over the wiring and may have found an issue, but my understanding of how it works is letting me down. As far as I understand it, the magneto system keeps producing a spark until the key is turned to off and earths the cut off wire and that stops the engine? When I test with my multimeter, the cut-off wire is connected to earth all the time. Even when I remove the wire from the wiring loom at the isolated post where it connects to the wire from the ignition coil, the coil appears to still be connected to earth. Is this correct or does it point to the ignition coil being faulty? If it's not this I think the carb will  need stripping down and refurbishing, maybe it's old fuel causing the problem, but it is firing when I turn it over so that doesn't make sense. I've tested for spark when it's turning over and there is spark.
I'd be very grateful for any pointers. Many thanks.

[Mick]

Hi, and welcome to TGMForum.

Try disconnecting the stop wire at that terminal or directly from the coil, and see if it stays running.  That will at least let you know if the coil is ok.  That said, it's also possible the wire has shorted between coil and terminal block.

Please keep fingers etc away from spinning parts while doing this and bare in mind you won't be able to turn it off, so you might need some insulated pliers to pull the ht cap off the plug. or reconnect the terminal on side of the engine.

[JHABT]

Many thanks for your reply. It's working properly now, I ended up taking the coil off, cleaning all the rust buildup off it and off the flywheel and magnet, resetting the gap and that appears to have solved my problems.

[Mick]

Nice job, thanks for the update. 

I've seen this a couple of times on modern equipment, it never used to be a thing in the past to be honest. They would run quite happily with quite major rust build up and corrosion.. 

Glad you got it solved though.