Kohler engine surging, seems to be governor

[s219]

I have an old 2002 Deere LT-150 mower that I no longer use for mowing, but have kept around for odd jobs. I have been thinking of selling it just to free up some space in my barn and hopefully someone else can put it to better use. It has a Kohler CV-15 single cylinder engine. Last fall it started running lousy and surging, then I couldn't get it to start a few weeks ago. I planned to clean and rebuild the carb, but found a brand new carb for $5 more than a rebuilt kit, and installed that yesterday. Got it started and it runs great but still surges.

I did some troubleshooting and it seems to be a problem with the governor. At higher speeds, I can see the governor throttle linkage going back and forth as the engine surges. If I hold the linkage steady with a finger, there is no surging and the engine is smooth. So that suggests to me that the surging is not due to a fuel/load problem that is being corrected by the governor, but is instead being caused by the governor itself.

I made adjustments to the governor as instructed in the Kohler service manual, and played with the spring setting, but all that does is change the response time and behavior -- doesn't get rid of the surging. So I'm left to thinking that there is an issue with the governor mechanism internal to the engine. Based on the service manual, it looks like a nylon or plastic gear was used for the governor (running off the crank) which then spins some weights that will go up/down and move a follower arm that goes through the block and out to the throttle linkage on the carb. Here's a pic from the service manual:



I am guessing that maybe the gear is worn or skipping periodically, or maybe there's an issue with the weights. But the surging is very smooth and seems to only happen at higher RPMs, and I don't think that would be happening if something was straight out broken.

I'm wondering if anyone else has dealt with this before and has any insight. The mower is probably not worth more than $250 or so. I don't think it will be worth the trouble to tear the engine apart to replace the governor parts. The thought crossed my mind that I could loosen the throttle linkage so that it's not affected by the governor, and that would probably be OK for basic use, but I don't want to sell it that way. I doubt it would behave well for mowing without a governor.

 

[Kernopelli]

Your governor may be working correctly and responding to fuel or air issues. You may have already done these but may be worth mentioning; Make sure the gas tank cap vent is working ( take the cap off and see if the surging stops). Check the air filter. Check/replace the fuel filter. Drain old gas, make sure there isn't any water that may be present in the tank left behind. Make sure the carb bolts are tight and not creating an air leak.

 

[JRobyn]

Surging on small engines is very often caused by a lean condition. Since the carb is new, any leanness is likely due to a vacuum leak somewhere.

 

[tomplum]

If your governor gear failed it would race. All you've got is the static governor adjustment out of the manual. If you bought a carb for a few bucks more than a kit, you've probably got a knock off. There in is likely where the problem lies. You could be looking at lean issue from a low float level from the seat not being fully pressed in or a restricted air bleed. All bets are off on what is inside these.

 

[s219]

As I mentioned, it was surging before with the old carb, so the problem is probably not related to the new carb.

I disconnected the governor shaft from the throttle linkage today, and the engine ran fine at all RPMs. So the surging seems to be caused by the governor somehow. I watched the end of the governor shaft and it's all over the place. Makes me wonder if the weights got loose or out of whack and are somehow simulating the changes in centrifugal force that would normally happen when the engine loads/unloads.

 

[eddie48]

There should be a spring wrapped around the governor link attached to the gov lever on one end and the throttle on the other. It keeps tension on the link to take up any wear on the holes where the link attaches. On an old engine this wear can cause surging. Is the spring there and not broken?

 

[MinnesotaEric]

Take a bottle of propane and stick a hose on it. With your engine running, turn the propane on lightly and using the end of the hose, probe around the intake manifold. If the engine smooths out, you have found an air leak. Stay away from the intake with propane otherwise you'll get a false positive.

On the other hand, I have a 5.5hp Toro single stage two-stroke blower that surges unless under a load and nothing is wrong with it, just the way the governor works.

 

[s219]

There should be a spring wrapped around the governor link attached to the gov lever on one end and the throttle on the other. It keeps tension on the link to take up any wear on the holes where the link attaches. On an old engine this wear can cause surging. Is the spring there and not broken?

The spring is there but barely has any tension. Seems like I have to move the throttle lever about 25% before the end of the spring catches on the throttle linkage and begins pulling the throttle/governor linkage. Then at full throttle, the spring just barely begins to stretch.

I have to say, I found that odd but don't know if it was always like that. So maybe I need to take the slack out of the whole setup so that the spring is under more tension?

 

[banjodunn]

G'day it is more than likely too lean on the idle mixture those small carbs rely on the idle circuit for part of the main jet fuel mix either that or it has the wrong main jet

Jon

 

[arkydog]

i have found on my engines surging most likely a stretched governor spring.