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Author Topic: HELP!!! WM Kohler Engine RPM Problems  (Read 8169 times)

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Offline DR_Buck

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HELP!!! WM Kohler Engine RPM Problems
« on: November 13, 2005, 09:50:58 pm »
To make a short story long........ ;D

I ran the LT-40 all day Friday cutting with no problems.    I set up Saturday at a customers place and cut about 5 hours and noticed the engine RPMs were higher than normal.  (Yes, I added the tach recommended by VA Sawyer in the "Saw Mill Mods" post)   Normal RPM for the Kohler 25 HP is around 1300 at idle and 3750 at full throttle.  However, idle RPMs were at 2200 and when I engaged the blade they went up to just over 4100 RPM.   I stopped and checked all the linkage on top of the engine connecting the throttle cable, carburetor and governor.  Everything seemed to be OK.  Nothing loose or stuck.   Shut down and went home.

Started back up this morning and everything was fine.    I did notice a slight  "pulsing" or "surging" of the engine when it was cold.  This was the 1st time I've noticed that.   After it warmed up the the RPM readings were right where they were supposed to be with no pulsing or surging.   Then......along around 2 PM all of the sudden the RPM jumped right back up to 2200 and 4150 again!   >:(   Still can't find anything wrong.

The engine is a 2003 25 HP with 266 hours on it. 

Any ideas ???   ??? ???
Hidden Acres Farm
I got a shotgun, a shovel backhoe and 57 acres!

Wood-Mizer LT40HDG25

Offline lamar

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #1 on: November 13, 2005, 10:05:09 pm »
I have a 25hp it was new a little over 3 yrs. ago no tack but sometimes I think I should get one. Mine had the throttle and choke right below the aircleaner and is adj. I added my on throttle control to put it where I wanted and made adj. hi and low stops. Now some of these engines are EFI then thats a whole new story.

Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #2 on: November 13, 2005, 10:45:37 pm »
Dave,
Did it actually sound faster? Could it just be an indicating problem? I have had both issues with my Onan. If I remember correctly, I had a small chunk of wood lodge in the linkage and it kept the gov from limiting max speed. It sure cut like heck (fast), but it sounded like heck too.
I also had a problem with the Tach showing some unrealistic high speeds. Tech Support for the tach company suggested unwrapping a couple of the turns the sense wire had on the spark plug wire. Said it was overdriving the input.
VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #3 on: November 13, 2005, 10:54:52 pm »


Quote
Did it actually sound faster? Could it just be an indicating problem?

It's not the tach.   The engine is definitely running faster.   Cuts like heck too.   I'm just worried about engine damage.  I couldn't find anything stuck in or around the governor linkage.
Hidden Acres Farm
I got a shotgun, a shovel backhoe and 57 acres!

Wood-Mizer LT40HDG25

Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #4 on: November 13, 2005, 11:03:05 pm »
Dave,
Engine damage is a real issue! I fixed mine pretty quick rather than letting it 'sing'. How does the gov on yours work? Is it centrifigal, or air ?  If centrifigal, is the clamp on the shaft tight where it goes into the case ?
VA-Sawyer

Offline DR_Buck

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #5 on: November 14, 2005, 06:11:50 am »
Quote
is the clamp on the shaft tight where it goes into the case ?

The clamp appears to be tight.    Strange thing is it only happens AFTER the engine is running for a few hours.
Hidden Acres Farm
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Offline twoodward15

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #6 on: November 14, 2005, 08:44:09 am »
Was the choke ever so slightly "on"?  That would lean things out a bit a it would rev up a bit more.  Maybe a piece of dirt in the carb or sawdust.
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Offline DR_Buck

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #7 on: November 14, 2005, 07:00:57 pm »
Quote
Was the choke ever so slightly "on"? 

Not the choke.  Something with the govenor mechanism.   Just don't know what or why it is OK for a while then speeds up.  ???
Hidden Acres Farm
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Offline PKAMWood

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #8 on: November 14, 2005, 07:19:41 pm »
Perhaps it's drawing a vacuum in the gas tank, causing it to run lean?

I'd be checking for a plugged vent for the tank, a clogging fuel filter, something like that.

Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #9 on: November 14, 2005, 07:59:02 pm »
Fellows,
This engine has its max speed controlled by a governor. It doesn't matter if the mixture is rich or lean, the governor will attempt to hold max RPM within the limits of WOT (wide open throttle).  Lots of things can cause an engine to be unable to reach max RPM. Very few will allow overspeed of a governor controlled engine. Failure of the governor is one. Failure of some kind in the governor to throttle linkage is another. Dave says the linkage appears OK, so the problem almost has to be in the governor itself.  Dave, have you talked to WM about this? I would like to hear what they have to say about it.
VA-Sawyer

Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #10 on: November 14, 2005, 08:53:25 pm »
Let me expand on how a governor controlled engine operates. When you move the throttle control to max, you are actually putting pressure on a spring. This pressure, usually tension tells the governor that you want more speed. Notice I didn't say power. Let's say you have moved the throttle control to its max position. The engine will increase its speed to max rated RPM. Under no load conditions, this may only require 40 % of WOT. As the load is increased it will cause the engine to lose RPM. The governor senses this RPM loss and opens the throttle just enough to maintain the set RPM. If the load continues to increase, the throttle will keep opening more and more to maintain RPM until WOT is reached. At this point the engines speed will start to fall off.  What happens next depends on the torque curve of the engine.

Lets assume that we have increased the load to the point where the throttle has just reached WOT and then increased the load just a little bit more.  If the torque curve of the engine peaks at the max RPM then as the engine is overloaded and starts to lose RPM it will lose HP and in this case torque. The RPM will rapidly decrease to the point of engine stoppage. This is like trying to drive away in a stick shift auto that is in 4 th gear.

Now, lets set up the same conditions except this time the torque curve peaks well below the max RPM. As the engines begins to lose RPM the HP decreases, but the torque available actually increases a little. This increase in available torque will tend to stabilize the RPM at a new lower level. This is actually an overload condition. The engine is bogging down some, but it is still running. The RPM is now directly related to the load. Any increase in load will further reduce RPM. Any decrease in load will cause the RPM to increase until max RPM is reached. If the load continues to decrease, the governor will again be controlling the RPMs. If the load is increased enough the RPMs will fall to a point below the peak of the torque curve. At this point the engine will again rapidly lose RPM and stop.

While not exactly correct, I tend to think of Torque as doing the work and HP determines how fast the work will be done.
VA-Sawyer

Offline twoodward15

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #11 on: November 14, 2005, 09:14:54 pm »
I understand how the governor works but you also have to remember that this isn't an exact science. These things were designed long before I was even thought of and haven't really changed much. There are certain conditions that WILL allow the engine to run faster even with a properly adjusted governor.  The reason I brought up the choke issue is because it works for me.  I have a race tractor, an older sears crapsman lawn tractor.  I can run this thing down the road and it is running at max governed rpm.  If I grab onto the throttle and ever so slightly pull it up (into the choke position for starting) it will overspeed the engine a little bit, depending on how smooth I am it can get up to about 250 rpm faster than the engines factory governed speed.   
    With my current setup and governed but playing the choke game it goes 28mph, clocked it with one of those speed showing trailers the cops put out on the street.  Gotta get some use of my taxes I guess!
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Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #12 on: November 14, 2005, 10:16:42 pm »
Dave,
On another post here on the forum, I found this link to the Kohler site:  http://www.kohlerplus.com/login.asp

Go there, use the guest login, go to the section on service manuals.
You want the manual  TP-2428-B  Go to somewhere around page 45. See if it helps.


twoodward15,
When you are pulling the throttle cable toward the choke position, you are also putting more tension on the governor spring and setting a higher set RPM. That works to a point because you are also closing the choke valve which will cause the engine to lose power. If you were to remove  the choke linkage, then you could get it to rev even faster, because the increased setpoint you are requesting from the governor ( by pullin on the cable ) would not be offset by the choke. You have a single cable controlling both the governor and the choke. If they were seperate, then adding choke would only cause a loss of power, and no increase in RPM or setpoint.

VA-Sawyer

Offline Percy

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #13 on: November 14, 2005, 10:30:27 pm »
To make a short story long........ ;D

I ran the LT-40 all day Friday cutting with no problems.    I set up Saturday at a customers place and cut about 5 hours and noticed the engine RPMs were higher than normal.  (Yes, I added the tach recommended by VA Sawyer in the "Saw Mill Mods" post)   Normal RPM for the Kohler 25 HP is around 1300 at idle and 3750 at full throttle.  However, idle RPMs were at 2200 and when I engaged the blade they went up to just over 4100 RPM.   I stopped and checked all the linkage on top of the engine connecting the throttle cable, carburetor and governor.  Everything seemed to be OK.  Nothing loose or stuck.   Shut down and went home.

Started back up this morning and everything was fine.    I did notice a slight  "pulsing" or "surging" of the engine when it was cold.  This was the 1st time I've noticed that.   After it warmed up the the RPM readings were right where they were supposed to be with no pulsing or surging.   Then......along around 2 PM all of the sudden the RPM jumped right back up to 2200 and 4150 again!   >:(   Still can't find anything wrong.

The engine is a 2003 25 HP with 266 hours on it. 

Any ideas ???   ??? ???
Heya Doc, I got the same motor on my WM edger. If Im not mistaken, the governor works offa oil pressure rise/fall. Id try changin oil/checkin oil/ change filter.  Ya might hava clog somewhere(tuff on motors ya!.)
Later
Percy
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Offline VA-Sawyer

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #14 on: November 14, 2005, 11:01:18 pm »
According to the Kohler service manual it has a flyweight ( centrifigal ) governor, or in some cases they use an electronic governor. Not sure which one Dave has.
VA-Sawyer

Offline Percy

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #15 on: November 14, 2005, 11:40:06 pm »
According to the Kohler service manual it has a flyweight ( centrifigal ) governor, or in some cases they use an electronic governor. Not sure which one Dave has.
VA-Sawyer

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Offline twoodward15

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #16 on: November 15, 2005, 07:45:35 am »
No Way Va sawyer!!  That's really good info for me.  I need to get this straight before I go try it.  You are saying that if I basically unhook the choke flapper that closes the carb during the choking of the engine that it'll let the motor rev up even more than I'm getting now?  WooHoo.  I'll try to get around to doing it and see how things work out.  thanks for the info.
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Offline bitternut

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #17 on: November 15, 2005, 08:22:52 am »
Oh boy........I can see one blown crapsman engine comin up. Lot of good info on engines in this thread.

Offline twoodward15

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #18 on: November 15, 2005, 02:13:35 pm »
Nothin like a blown crapsman engine to start your day.  It was a free tractor anyway and I think I have all of about $5 into it.  It's a pretty good motor (I hope) we'll see how it holds together.
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Offline sparks

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Re: HELP!!! WM Kohler Engine RPM Problems
« Reply #19 on: November 16, 2005, 05:47:20 am »
Dr buck, Give Greg Brock a call here at Wood-Mizer. 1-800-525-8100. He's our engine man and can aim you in the direction to find the problem.   Thanks
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