Well Of Course...

[DavidBarkey]

The machine will run at WOT perfectly happily now, as long as it's just sitting there. It will move around at low to mid speed pretty reliably. High speed will cause the stall. Not instantly, but randomly./quote]

Things to look at .
Spark plug / colour and wet or dry , condenser , coil /is there spark , ignition switch / does coil have power , wiring / same as coil, voltage regulator / voltage and how much AC volts are there . when dies.

these are great for diag. can run tractor with it on until dies and immediately know if it is spark related .

Spark plugs, coils , condensers , and ignition switches can all go open when hot/underload then come back when cool some . When in dought replace each one , one at a time with know good unit . New doe Not necessarily mean it is "good" .

Happy hunting .

[JSinMO]

I’m try to think of quick ways to test this since it’s intermittent. I agree with you @Toolslinger , I’d much rather something to just break.

Mr Daves in-line spark tester is a great idea. You can watch spark in real time. I need to get one for my tool box. No blinking light=no spark.

Maybe you can carry a can of carburetor cleaner with you. When this happens squirt the around the carburetor. If engine rpm picks up then it may be fuel delivery or a vacuum leak. You may want to do this with the air cleaner off.

I’m trying to think of a good way to test the hydraulics. When it happens will the engine stay running if you put the tractor in neutral? Or when it happens is it possible for you to see flow in the tank?

Would it be possible to run the engine under load with the PTO and not move the tractor? That would isolate the engine from the hydraulic system and maybe narrow things down.

I’m just thinking out loud hoping to help get the problem isolated.
Let us know what you find!

[Toolslinger]

Just another bit of info that I see I didn't post...
When it starts to die, if I stop movement, that doesn't seem to save it. However, if I stop movement, and drop it down to idle, it will continue to run.

Spark tool is an excellent suggestion. I have one, so that will happen tomorrow I think. I need to pull the hood off to use it, but that's fine.

Condenser. Haven't checked that. Had to look up how honestly, but that's about as simple as it gets to do. Will hit that tomorrow as well.

Coil... Well I did just do it, but as noted, that doesn't make it good. Will throw a meter on that as well. I really don't want to replace that again, but if I do, at least I can find one that isn't bright yellow this time...

I was thinking about running something on the PTO. I've got a tiller, a post hole digger, and a hydrovac. The vac is new to me, so not knowing it, that's not what I'd test with... The other two I haven't run in years, but there's no reason they shouldn't perform as advertised. I guess the tiller would be the easiest to put under load, plus it's way easier to hook up than the auger.

Planning to put a meter on some things, and jiggle wires to see if I get any movement in the needle. Never been a big analog meter fan, but for this, it is likely a better choice.

Is there a spec on fuel flow rate? I can always pull the line in to the carb and time filling a measuring cup. I suppose I could try to find the spec on the pump as well. I know it can move enough fuel to keep up with the Kohler unless it's gone bad, I have the same pump on both my 646's with no issues, and they're a little more thirsty.

[DavidBarkey]

FYI . internally resisted coil will be between 3 and 4 ohms .
externally resisted will be between 0.5 and 1.5 ohms .
A externally resisted coil without a resister will not only cause the points to fail premature but also can cause the condenser to over heat and act up.
Check the values to make sure you have the proper one for the application . I have gotten the wrong one before because it was boxed wrong . They do look the same on the outside .

[myerslawnandgarden]

The thing that jumps out to me after reading this thread is that "if I drop down to idle after it begins to die, it will continue to run". If no spark, that would not occur. Sounds like a fuel starvation issue to me, but cannot rule out a hydraulic problem although they are much rarer. If it begins to die, have you tried to quickly close the choke to confirm that it's a fuel issue?

Bob

[Toolslinger]

If it begins to die, have you tried to quickly close the choke to confirm that it's a fuel issue?

I have not tried that. Certainly can't hurt to try.

Having just put on a new carb, and the problem being the same, I really don't suspect an issue there. What are the odds a 40 year old carb, and a brand new one show up with an identical issue? That said, it could sure be fuel delivery before the carb.

[DavidBarkey]

If it begins to die, have you tried to quickly close the choke to confirm that it's a fuel issue?

I have not tried that. Certainly can't hurt to try.

Having just put on a new carb, and the problem being the same, I really don't suspect an issue there. What are the odds a 40 year old carb, and a brand new one show up with an identical issue? That said, it could sure be fuel delivery before the carb.

It still could be fuel starvation problem from two different carbs , but for two different reasons . Also , enriching the mix a bit will help a week spark jump the gap . So still could be be ignition related if a little choke helps . I would still have the tattle tail spark tester on when you do it and watch how the light reacts when the choke is applied when it is dyeing .

First thing to do is to run it and let it dye watching the light and check the spark plug . Is it wet / dry/ tan / black . That will tell a lot on which way to start looking .

[Eugen]

@Toolslinger , you got a lot of good suggestions, so I'm not sure anything I say would be helpful. It's a puzzling issue you're facing, and yes, intermittent issues are the worst. That being said, here's the way I see it. Something you said: that when at or near full throttle it doesn't die unless you try moving, makes me think that it's not hydraulic, or spark related, but fuel starvation. What happens when you try to move is that the load on the engine increases, and the governor should pull on the carb tab and more air/gas get in the cylinder.

To bypass the tank you could put a fuel line in a clean jug with gas that you tape to the top, or something like that. Make sure the carb main jet is 3-4 turns out from the bottom.

You'll figure it out I'm sure, however annoying it is, it's good that it's not something catastrophic like rod through the engine.

[Toolslinger]

Ok gents, I put alittle time in over the weekend...

I looked in the tank, which I had done previously, but this time, I saw some crud in the outlet. There's no screen on the tank outlet, so anything that gets near it, is going out... I was also surprised that I don't in fact have a filter on the line. I was sure I did, but apparently not.

At any rate, that meant I got to rip everything apart and clean the tank out. After that, I checked fuel flow from the tank out the line at the carb inlet, and I have plenty of fuel comeing down the line.
Since there was crud involved, I pulled the carb, and gave it a quick clean. I went back to initial carb settings. I was a bit lean in comparisson to the initial point, but not crazy, so I didn't think it was just that.

Started, and ran it for a while. Had to work on the carb a bit to get it to idle happily, and then run up to full.

Ran it outside, and found I basically had the same issues. I did remember to try throwing in the choke when it was dieing to try that. Didn't help.

So I threw the spark checker on it. Seemed ok. Ran it WOT for a bit, and it would miss now and again. Checked the spark, and yea, it was definatly missing spark at those times.

So, I think I'm now looking at ignition. I did not run it around to cause the stall as I was about out of light, and I was cold to boot. I'll do that next chance I have with the spark checker in place. I have preemptivly ordered a coil, condensor, and points. If I don't find a smoking gun in the coil, or cap, I'll do the points, and check the push rod. Doesn't hurt to have them on hand anyway, most of my equipment would take the coil, and cap if needed, and there's two other Kohler's that could take the points. Napa coil, and Kohler points, and condensor.

[JSinMO]

That’s good progress on the troubleshooting! I just saw a video today of a guy that had intermittent trouble in his ignition system. In his case it turned out to be the ignition switch intermittently going to ground due to a loose connection.
It probably wouldn’t be a bad idea to check the wires or just replace them.
Looking forward to what you find.