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I have a 2005 Exmark Lazer Z 60" with a 25 Kohler. I have been chasing a loss of power issue for the past couple weeks.

Compression is 130-135 on each cylinder
Replaced all fuel lines, filter, and pump
Replaced air filter
Plugs are clean
Cleaned carb
Replaced intake and exhaust manifold gaskets
All pulleys are rotating fine

Mower idles and throttles up fine but once you put any load on it, it bogs down.

Any thoughts or help would be greatly appreciated.

zmcg1995 said:

I have a 2005 Exmark Lazer Z 60" with a 25 Kohler. I have been chasing a loss of power issue for the past couple weeks.

Compression is 130-135 on each cylinder
Replaced all fuel lines, filter, and pump
Replaced air filter
Plugs are clean
Cleaned carb
Replaced intake and exhaust manifold gaskets
All pulleys are rotating fine

Mower idles and throttles up fine but once you put any load on it, it bogs down.

Any thoughts or help would be greatly appreciated.

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Have you checked to make sure you're actually firing on both cylinders? Also are you losing/burning any oil?

solefate said:

Have you checked to make sure you're actually firing on both cylinders? Also are you losing/burning any oil?

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Yes I am running on both cylinders and I have some small oil leaks but nothing major.

Have you checked to see if both cylinders are firing and carrying their part of the load. You may be running on one cylinder. If you have a good pair of insulated pliers, run the engine at 1/2 throttle and while it is running pull the spark plug wire off, one cylinder at a time. Engine should loose speed when you plug the plug and regain speed when you push it back on. If nothing changes when you pull the plug wire, that cylinder is causing your problem and you’ll have to figure out what’s wrong.

I have done that and it lowers to the same speed when I unplug each cylinder.
So it is indeed running on both.

zmcg1995 said:

I have done that and it lowers to the same speed when I unplug each cylinder.
So it is indeed running on both.

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Any oil leaking from head gasket? Or excess gas coming out or burning off in the muffler?

Does the governor kick in under load? Does the engine spit and sputter under load? Does the engine or blade speed bog down?

solefate said:

Any oil leaking from head gasket? Or excess gas coming out or burning off in the muffler?

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No oil leaks from head gasket. I had an oil leak from the head gasket and I fixed that and that actually seemed to be when the issue started. I believe if I had a blown head gasket I would lose compression in that cylinder.

Remove the muffler or at least loosen the exhaust flange bolts. Run it up to see if it continues to pull properly. If so, your muffler is being restricted by a collapse inside. Doesn't happen often in the mower world. However, it does happen.

Rivets said:

Does the governor kick in under load? Does the engine spit and sputter under load? Does the engine or blade speed bog down?

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It doesn't seem like it does. That seems like that is what is missing. It doesn't spit or sputter but it just bogs down. The engine and blade speed bogs down.

mhavanti said:

Remove the muffler or at least loosen the exhaust flange bolts. Run it up to see if it continues to pull properly. If so, your muffler is being restricted by a collapse inside. Doesn't happen often in the mower world. However, it does happen.

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I actually tried running it briefly without the exhaust on to see if there is indeed a blockage and didn't change anything. There is also plenty of pressure coming out of exhaust.

zmcg1995 said:

I actually tried running it briefly without the exhaust on to see if there is indeed a leak and didn't change anything. There is also plenty of pressure coming out of exhaust.

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Not sure if this is advisable, but seems like if you could play with the linkage while simultaneously bogging it down you could check the governor?

solefate said:

Not sure if this is advisable, but seems like if you could play with the linkage while simultaneously bogging it down you could check the governor?

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As in just open the throttle all the way when it starts to bog down?

zmcg1995 said:

As in just open the throttle all the way when it starts to bog down?

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More or less. You'll basically be forcing the job of the governor.


/edit If you can stand it, you might wait for Rivets to post lol. He knows way more than I do.

Rivets said:

Does the governor kick in under load? Does the engine spit and sputter under load? Does the engine or blade speed bog down?

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Any thoughts?

One thing that hasnt been mentioned yet are your blade bearings. disconnect belt and make sure each blade spins easy. There should be no side to side play. Also double check the valve lash on both cylinders. Also you could try taking your carb intake off and check the intake port of the heads. Bad gas over time will build up a honeycomb of corrosion that will rob power.

Have u checked the push rods to make sure one isn't bent or out

Since this engine doesn't use compression release your readings of 130-135 are low according to what Kohler list in the service manual for this engine. Kohler says 160 should be the mininum, so I think I would be looking into a leakdown test next to try to find the cause of the low compression. This engine doesn't have adjustable valves because of the hydraulic lifters, and if one of the push rods had come out it would be running on one cylinder and when you removed the spark plug from the good cylinder the engine would of died. So I don't think it is a valve issue but may want to pull the rocker covers and rotate the engine through a couple revolutions to make sure the valves are opening about the same amount to rule out cam lobe lift wear.

Something else to consider is a partially clogged main jet in the carb, since the engine only uses that jet when the deck is engaged and the engine is under a load.

I agree with I’ll, about checking the main jet. Another thing I would check is, What RPMs are you running at? I set those engines at a minimum of 3200. If you can give us a better picture of what is happening. You say loses power under load. What type of load, when you kick in the PTO, normal mowing, heavy grass, going up hill PTO off? Do you operate the unit at full throttle when cutting? Remember we are not there to see what you see and hearwhat you hear. The better the picture you paint, the better info we can give you.