STEVEN H GEORGE 0 #1 Posted June 28, 2021 (edited) Hello All! I'm having a big issue with my 1999 Wheel Horse/Toro 520xi that I've owned since 2013 with never a problem before. I would very much appreciate any ideas or pointers. I will list all the symptoms first: 1. The electric PTO engages fine when I first start the mower but, after about 1/2 hour of mowing time, if I disengage it, it will not reengage until I let the mower cool down. 2. The red Battery Charge light on the dashboard is always on when the mower is running. Even after I replaced the battery with a new one this still occurs. 3. I never have a problem starting. This problem only begins after the engine is warmed up and I mow for 1/2 to one hour with PTO engaged the whole time. 4. When I disengage the PTO to put mower away OR mow for over 30 minutes, the engine begins to surge to very high RPM and the throttle will not lower the RPM so I need to use the choke to control it. 5. When I turn the ignition off, the engine dies but backfires once. 6. I disconnected the PTO harness did a resistance check of the PTO wiring and found it normal and not grounded (3.4 Ohms) I'm completely baffled by this issue and not sure what to check next. Any help would be awesome . Thanks in advance Model # 73540 Serial # 8901132 Engine CH20S Engine Spec : 64583 Edited June 28, 2021 by STEVEN H GEORGE add additional info Share this post Link to post Share on other sites
Handy Don 13,465 #2 Posted June 28, 2021 Welcome to the forum! This is definitely the place to ask questions like the ones you have--as long as you are ready to get a variety of answers based on different members' experience and opinions. I have very little experience with the 520xi so I can only offer general comments. According to the 522Lxi manual, the battery light staying on is NOT a good thing and indicates a problem with over or undercharging. Not something you should allow to persist. Since it starts and the battery seems to be staying charged, it seems like the voltage regulator may be permitting the voltage in the tractor to go too high. This could damage the battery itself as well as other components, including the electric PTO or the cruise control, or even the gauges and other indicator lights. I have no idea if there is an electrical interaction with the governor on this tractor that could be related to the runaway to high RPMs. Firstly, please get the model and serial number of your tractor and post it here so we'll know which documents cover your machine. The admins here have a lot of manuals and documents so the more specifics the better for zeroing in on the right ones. Secondly, by all means, use the search box to scan the site for other information--you can filter the search to look in only the Documentation section to help you find the manuals and wiring diagram. Share this post Link to post Share on other sites
STEVEN H GEORGE 0 #3 Posted June 28, 2021 48 minutes ago, STEVEN H GEORGE said: Additional info about my 520XI which has the issue: Mower Model: 73540 Engine Model: Kohler CH20S Engine Spec : 64583 Carburetor: 24853305S Share this post Link to post Share on other sites
Handy Don 13,465 #4 Posted June 28, 2021 2 minutes ago, STEVEN H GEORGE said: What are the model and serial on the fender tag near the seat? That's the info that identifies the wiring and build. Share this post Link to post Share on other sites
STEVEN H GEORGE 0 #5 Posted June 28, 2021 Model Number : 73540 Serial Number : 8901132 Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,284 #6 Posted June 28, 2021 Welcome to Red Square Here are some good wiring diagrams. The major components have there own diagram. Garry Share this post Link to post Share on other sites
Handy Don 13,465 #7 Posted June 28, 2021 Quick followup after scanning the maintenance manual. I suspect you have two different problems. The electrical one, which could be the result of bad grounding or a bad connection in one of the circuits (heat expansion could easily affect corroded or poor electrical connections) or the result of a bad voltage regulator. The service manual has good diagnostics for checking the electrical components. You need a volt-ohm meter for that. The run-away one, which is likely to be related to a mechanical issue with the governor. I didn't see any throttle-controlling electrical components that could be involved. Another member is likely to come along with other comments! Good luck Share this post Link to post Share on other sites
STEVEN H GEORGE 0 #8 Posted June 28, 2021 Yes , Don. Thanks. I agree. I just went out and but a dc voltmeter on the battery with mower off. I measured 12.45 VDC. Started up the mower with no load and the meter never moved; stayed at about 12.45 VDC. So at least the regulator is most likely bad. The engine raced again today right off the bat and I had to choke it down before it blew. Shut it down and checked to see how to get at the regulator. It seems to be stuck up inside the plastic engine shroud. I'll have to do some research on how to get at it. I'll keep posting updates here. Who knows, someone else might have this issue later. Thanks! Share this post Link to post Share on other sites
Handy Don 13,465 #9 Posted June 28, 2021 5 minutes ago, STEVEN H GEORGE said: Yes , Don. Thanks. I agree. I just went out and but a dc voltmeter on the battery with mower off. I measured 12.45 VDC. Started up the mower with no load and the meter never moved; stayed at about 12.45 VDC. So at least the regulator is most likely bad. The engine raced again today right off the bat and I had to choke it down before it blew. Shut it down and checked to see how to get at the regulator. It seems to be stuck up inside the plastic engine shroud. I'll have to do some research on how to get at it. I'll keep posting updates here. Who knows, someone else might have this issue later. Thanks! The service manual has a section (with pictures!) on how to access the regulator. Good luck! Share this post Link to post Share on other sites
slammer302 2,156 #10 Posted June 29, 2021 I have a 520xi had the same problem with battery light coming on replaced voltage regulator it fixed the light coming on . My clutch still does not like to come on after running the deck for along time I can hear it trying to come on I took it apart the disc had lots of wear on them so I just assumed it's getting worn. I have had to adjust throttle cable more than once at the set screw just before the linkage. Share this post Link to post Share on other sites
STEVEN H GEORGE 0 #11 Posted June 29, 2021 Thanks for the advice sirs. I do think I have more than one problem too like mentioned above. Either carburetor linkage problem and maybe a PTO clutch going out. But I think a may have isolated my main issue today thanks to some help from here today. Here's the latest: - I found and disconnected the harness going from the magneto to the rectifier and verified I had the 24 VAC going into the rectifier. - Then I checked the output (B+) coming out of the rectifier with respect to battery negative (-). I was surprised to see NEGATIVE 5 volt DC! - I thought i was seeing things so I double checked my meter setup and the polarity of my leads and sure enough I was getting negative out - When I reved up the engine, the voltage went up but was still negative - I decided to order a new rectifier/regulator; part number 25-40303, from Ebay for $14. I'll post here the results when it arrives. NOTE: It's almost impossible to get to the rectifier on a Kohler Command CH20S because is mounted behind both the engine shroud and the mower frame. The manual says to remove or loosen all the engine mounting bolts- a nightmare to say the least. When the new rectifier arrives, I'm going to abandon the old one in place and I'm going to grind off the paint on the frame and mount it right there so its easy to to reach and out of the way of moving parts and debris. I'll be sure to properly ground the rectifier case as the service manual calls for. Wish me luck! Share this post Link to post Share on other sites
Handy Don 13,465 #12 Posted June 29, 2021 (edited) 1 hour ago, STEVEN H GEORGE said: and I'm going to grind off the paint on the frame and mount it right there so its easy to to reach and out of the way of moving parts and debris Interesting approach! If you have the slack in the wiring harness, I'd guess it'll work. A sticky link or weak spring in the governor linkage could be the source of the runaway. Thorough clean and lube will either solve it or eliminate it as a possibility! As an aside, to avoid miscommunications, the thing you ordered does have a rectifier (or two or three) inside, but it is a voltage regulator. Also, your engine doesn't have a magneto (which would provide timed energy pulses directly to the spark plugs), it has an alternator that supplies that AC juice to the voltage regulator. The VR feeds DC to the battery, and coil and also to an ignition module that times the energy pulses from the coil to the plugs. Edited June 29, 2021 by Handy Don Share this post Link to post Share on other sites
gwest_ca-(File Mod) 11,284 #13 Posted June 29, 2021 The regulator is mounted on the blower housing for a reason. That is what cools it. Garry 1 Share this post Link to post Share on other sites
