My Lawnmower Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
Engine will sputter and start to die after 10 to 15 minutes mowing, but will not completely stall if I quickly turn off blades and use full choke (clock display goes blank as this happens). After a couple of minutes, the display returns and I can remove the choke to smooth it out and restart the blades. This continues to happen with increasing frequency unless I disconnect the regulator/rectifier, which prevents further problems (replacing the regulator/rectifier did not solve the problem). Twice the engine refused to restart after a normal shut-down (with the key). Display remained blank for several minutes until it suddenly reappeared and engine could be restarted normally. Two snapper dealers have been unable or unwilling to solve the problem. So far, I have replaced the regulator/rectifier and the seat safety switch. I now suspect either the safety switch that keeps the engine from starting when the PTO is engaged, or the safety switch that prevents the mover from backing up when the blades are engaged (unless a dash lever is activated). I need wiring diagrams and operation details of these two safety devices before I can continue my search for an answer. Any help in diagnosing this problem will be appreciated.
 

·
Administrator
Joined
·
6,234 Posts
Welcome to the forum bmarrj! :welcome:

...This continues to happen with increasing frequency unless I disconnect the regulator/rectifier, which prevents further problems (replacing the regulator/rectifier did not solve the problem). ....
There must be a big clue there if we can figure out what it points to. The clock going blank would indicate a loss of 12 volts to it. At first I thought maybe a cell in the battery intermittently shorting out or another connection issue to the battery. But when you mention it working after pulling the regulator/rectifier out, that would mean it was running off battery ok without any recharging occurring from the engine alternator.

Is the rectifier connected by a 3 pin plug? I may well be totally off the wall but I'm actually wondering if you could have an intermittent short either the flywheel stator or the wiring to it which would be removed from the circuit by pulling the regulator plug.

Makes it harder not having a specific wiring diagram for the mower at hand. I looked up an engine manual for what I think is the engine on your tractor, a Kohler Command 25hp. horizontal shaft twin cylinder. Take a look at the manual linked below and specifically starting page 34 of the electrical section and see if that looks anything like yours.

http://www.kohlerengines.com/onlinecatalog/pdf/sm_24_690_06.pdf

If this is not your engine you can look up the service manual for other models here:

Kohler Engines: Owners and Service Manuals: Manuals and Maintenance
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #3 ·
Good Analysis

My Kohler 25 hp engine is model: PS-CV730-0051, SN: 3733105101 and does have the 3 pin rectifier. If the flywheel stator or wiring shorts, it could lower the battery voltage enough to interfere with the clock and partially shut the fuel solenoid. Is there a way to test this intermittent shorting prior to dismantling the engine? Would monitoring the battery voltage during one of these episodes (rectifier connected), confirm your suspicions? Do you then believe that the second part of my original post is a second fault? I was looking for something that could explain both faults, but could only guess that it might be connected to a safety device (such as the one that kills the engine if the tractor starts to go into reverse with the blade on, prior to overriding the safety device). I was unable to find anything specific to my Snapper GT25540, model 2690742, s/n 2012730845 about the safety devices. Do you have any info about these? Thank you for taking the time to help me with this problem.
 

·
Administrator
Joined
·
6,234 Posts
My Kohler 25 hp engine is model: PS-CV730-0051, SN: 3733105101 and does have the 3 pin rectifier.
Looks like I guessed close but not quite. :) A vertical shaft then would be this service manual:

http://www.kohlerengines.com/onlinecatalog/pdf/sm_24_690_07.pdf

... Would monitoring the battery voltage during one of these episodes (rectifier connected), confirm your suspicions?
That's a good thought to try. I would measure several places starting with the battery terminals, then the output on the regulator and at the clock if possible. Then note if it is a low reading at one or all or none of the places. Also check, tighten every place you see a wire going to chassis ground or other power terminals such as on the starter.

Do you then believe that the second part of my original post is a second fault? I was looking for something that could explain both faults, but could only guess that it might be connected to a safety device (such as the one that kills the engine if the tractor starts to go into reverse with the blade on, prior to overriding the safety device).
I suspect you'll find they are related to the same cause but don't really know. I noted some more advanced electronic controls on the ignition on some models in the manual. Electronics can be picky about the quality of power they are receiving. Voltage variations or even noise from a poor connection can cause them to work erratic.

I was unable to find anything specific to my Snapper GT25540, model 2690742, s/n 2012730845 about the safety devices. Do you have any info about these? ...
Unfortunately no. I looked on both Snapper and Simplicity websites but found only operators and parts manuals with no wiring information. I would imagine you could order a technical manual from them with that information.

Lawn Mower Manuals | Snow Blower Manuals | Snapper Customer Support

Simplicity User Manuals and Instructions

FWIW, I'm not a professional small engine tech nor work in the lawn and garden field. So I don't have access to any manufacture specific or dealer tech tips, diagrams, etc. Nor am I up on all the specifics of the electrical controls on the newer models. I'm just a fellow like yourself who owns a tractor and several lawnmowers and volunteer my time here hoping to help someone else sort through a problem like I've been helped by forums like these in the past. :)

It concerns me a little that two Snapper dealers were unable to solve this. The concern being that it is some little oddball issue that either you would never look for or would never think it would cause the problem that it is. :confused:
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #5 ·
New Info

A preliminary voltage test indicated no substantial change at the battery, but DC voltage was nearly zero at the connected regulator during an episode. I tried measuring the voltage from B+ to ground and B- to ground at the regulator and my ac/dc meter also showed dc voltage near zero for both (between episodes, these same readings were 13 vdc, which I would have thought would be AC not DC). I will look for a different meter to see if I can measure AC voltage during or between episodes. Any idea why the voltage is not the same at the regulator and battery, since they appear connected at the solenoid on the wiring diagram? I will try cleaning the solenoid connections and if I still experience episodes, will connect the regulator directly to the battery without the solenoid connected. Any other suggestions?
 

·
Administrator
Joined
·
6,234 Posts
I'm not seeing the "B-" terminal in the diagram. :confused:

On the regulator I see the two outside pins labeled "AC" which go to the coil under the flywheel. I would expect to see AC voltage on them but I would not think there should be any DC there. Then the center "B+" terminal goes to the solenoid stud where it is tied to the wire from the positive terminal to the battery.

Also I was looking at page 46 of the manual. They show both resistance and voltage readings for the stater coil there.

Back to the clock... If you can find which is the power lead to it and trace it back to the battery or regulator. The power line to the clock could also be power to relays activated by the safety switches. Keep in mind the Kohler manual is only a general diagram and Snapper may have made some modifications to better fit their application.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #7 ·
Update

Mark, one of the two outside AC terminals is marked B- and the other one B+ on the regulator. I used an oscilloscope to view the outputs from B- to ground, B+ to ground, B- to B+, and from the center terminal to ground. During normal operation with the regulator connected, the center terminal to ground is 12 volts dc, and all connections involving B- or B+ show ac volts (my original meter must be mistaking half-wave ac for dc voltage). During an episode, all voltages are reduced while voltage across battery remains at 12 volts dc. On the wiring diagram, it appears that the B- and B+ connects directly to the Flywheel Stator Assembly (is there a test to confirm its operation)? Not sure how a short in the wiring would make both AC voltages to be low, or why this would cause the clock to go blank. Of course, the wiring diagram we are using is for the Kohler engine and it might have been modified when it was placed into the Snapper Tractor. Wish we had a specific wiring diagram for the tractor. By the way, the fault now occurs within 2 minutes while mowing, and will cycle (bad then good) with the blades off, and engine rpm at minumum (even without using the choke).
 

·
Administrator
Joined
·
6,234 Posts
.. On the wiring diagram, it appears that the B- and B+ connects directly to the Flywheel Stator Assembly (is there a test to confirm its operation)?...
I'm not aware of any other stator tests that could be done other then those listed on page 46 in the Kohler manual without specialized equipment one possibility being a ringer tester. But even if you had one they do not give you any nominal values for comparison to yours in the service manual and it often times was not a 100% anyway.

(Still turned out in the end to be a bit of a guess back in the day when once in awhile we ring tested TV deflection coils and high voltage transformers.)

I'm still wondering if if that stator could be intermittently grounding out to the engine block someplace within the coil causing the problem. But outside of measuring the resistance from B+ and B- to ground with the regulator disconnected and visually looking at it for any signs of heat (blackened-burned or un-coated wire touching the steel core) I don't know of another way to prove it out.
 
1 - 8 of 8 Posts
Top