850 running rough....need to cut hay!

Loaded up the 850 & sickle mower today. Went to my sister's house and began cutting her 5 acres. All was going well at first although it seemed to be missing a little at 1500 rpm (where I need to be with the sickle mower). It idled fine. As time went on it ran rougher and rougher until finally I had to limp back to the house.

It felt like fuel starvation at higher rpm, but I've heard about all the "fuel" problems that end up being in the ignition system. I've also heard about the notorious weak key switches. My key switch has been in place for at least 10 years so I figured maybe this was it's time. I tried to pull the wires off the switch so I could bypass the switch (no jumper wires at hand). Ended up breaking off the terminals off the back of the switch.

Went to O'Reilly Auto Parts (only place in town still open at 7:30) and bought a toggle switch....best I could do. Went back to the tractor, wired the toggle switch up and it started. Still sounded a bit rough but I was able to cut a few more passes before it got ragged again. Pulled it up next to the garage and squirted some carb cleaner into the idle screw opening and into the power valve opening. No time for a rebuild and no kit on hand anyway. Also pulled off the sediment bowl and squirted carb cleaner through the top screen. It didn't look too dirty.

Started back up and cut some more. It was running a little better, but not great. I was just trying to get as much cut before dark as possible. Finally as I was making a turn my left rear wheel fell into a depression. Not deep enough to get stuck, but enough to make the tractor lean to the left noticeably. As soon as I did, the engine quit and would not restart.

Walked back to the truck and got my meter. I have 6.23 volts at the battery, at the new toggle switch and at the coil where the ignition wire connects. However I have nothing at the other coil terminal that is connected to the distributor. I can only conclude that I'm not getting any voltage to the points. This is a 6 volt round can coil on a 172 Red Tiger engine.

Tomorrow I'll dig up an old coil from the collection and try that. I'm open to any other suggestions. Thanks!

Sorry your reading got to long for me but maybe I can help any how. First off check for a good spark that will jump a 1.4 inch gap does not matter if coil or plug wire. But if you can not get it at both then you have a rotor or cap problem. Weak ignition switch can happen but not all that much with the 850. One other thing to check if a good fuel flow at the carb drain plug. If you do not get a steady flow there then work you way back from there you should be able to fill a pint jar in less then 5 minute at the drain plug

Jim,
My 851 acted like that a couple of years ago and it was the condenser that was causing the problem.
The engine dying when the left rear dropped sounds like a wire moving and shorting out. Is the wire from your coil to dizzy good? Is the insulator in the side of the dizzy good? The little copper strap inside the dizzy?

Sure sounds like fuel to me, but I suppose an electrical ground could do it.

Coil won't show voltage on dist side if points are closed, grounding it out . . . will it???

you are correct. sice the points go to ground, if they are closed there will be no volts 'showing' on that side of the dizzy.

IMHO.. he has fuel problems if it has spark when he can get it to run..

soundguy

It is very difficult to tell when a 172 is missing; they can run on three and even two cylinders and seem to be running OK. Make sure you don't have a missing cylinder (or two) by pulling the plug wires off one at a time with insulated plug wire pliers.

He had an open coil primary...replaced & cutting hay. :lol: