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Discussion Starter #1 (Edited)
I've got a 2009 Cub SLTX 1054 with a Kohler Courage 26 v-twin engine. Last fall, the engine started losing power. By the time we parked it, it could barely climb a hill with the blade engaged. With the blade disengaged, it's better, but still noticeably underpowered.

Earlier this Spring, I finally looked into it. New air filter, although the old one wasn't terrible. Spark plugs were fine, and there's good spark from both of them. New fuel filter, although the old one seemed OK. Changed the oil & filter, and found that the old "oil" resembled black gasoline. The fuel pump had a ruptured diaphragm, which leaked fuel through the valve cover into the block. Replaced the fuel pump. Disassembled & cleaned the carb, although it looked fine inside. Each cylinder has about 135 psi of compression, although that leaks down very quickly as soon as I stop cranking the starter.

When I took it out for a spin last week, I found that it's still underpowered. It can now climb a steep-ish hill with the blade engaged, which is better than it was, but only barely. It sounds like it's running fine. No discolored exhaust.

What should I look for next? Fortunately, we have a spare lawn tractor, but we like the Cub better when it's actually working, and would really like it to be working again.
 

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maybe check compression on both cylinders? Gas in oil isn't good, as it significantly reduces the oils ability to lubricate and cool the engine, as well as the oil level is too high, so the crankshaft is more likely to aerate the oil by causing it to splash around more.
 

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do a compression test.
it sounds like the engine wasn’t getting adequate lubrication with the gasoline - oil mix,
and so the cylinders are probably scored
 

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B
maybe check compression on both cylinders? Gas in oil isn't good, as it significantly reduces the oils ability to lubricate and cool the engine, as well as the oil level is too high, so the crankshaft is more likely to aerate the oil by causing it to splash around more.
Beat me to it!
 

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Discussion Starter #5
Looks like I was editing my original post as you guys were replying. I did a compression test. Both cylinders have ~135 psi of compression, which seems fine.
 

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are there any oil leaks? When oil is thin, It usually escapes past the seals that don’t leak with proper oil. Maybe the bottom crankshaft seal was leaking and oil got on the drive belt causing it to slip?
 

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Yeah, if the engine isn't slowing down when you go uphill, then the problem is more likely after the engine, oil on the belt or perhaps a coincidental problem with the drivetrain.
 

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Discussion Starter #8 (Edited)
The engine is noticeably underpowered even with the PTO off. Turning the PTO on just exacerbates the problem. The engine itself sounds fine (without the PTO, anyway)--the tractor just moves like a lazy dog. With the PTO on, the engine slows down somewhat as it's working harder.

There is (or was?) an oil leak somewhere--perhaps everywhere--because the entire lower half of the engine and undercarriage was caked in oil-soaked dirt. Took the better part of a day to clean & degrease it. A day after my short test drive, I found a small leak (maybe oil or dirty gas) below the front half of the engine. It might be coming from the vicinity of the back of the carb, but I didn't take the time yet to diagnose exactly where.

A few years ago, I had to replace the transaxle because I pulled something too heavy & burned it up. I know what that feels like. This isn't a transaxle problem.
 

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When you do a compression test does it hold the pressure? I know you said 135# but does it hold it. Might be time for a topend rebuild.
Especially if your sure the rear differential is operating properly and all other drive components are operating properly then a topend is probably in order.
 

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Discussion Starter #11
So the engine is slowing down when you go uphill?
It slows down somewhat up the steepest hills, as though it's bogging down under load.

When you do a compression test does it hold the pressure? I know you said 135# but does it hold it. Might be time for a topend rebuild.
No, after I finish cranking the starter, the compression drops rapidly.

This doesn't feel like just wear & tear from old age, though. The Cub was running fine mid-summer, and then over the course of less than a month became completely gutless. It's as if something happened to it.

If I did do a top end rebuild, what am I looking for, specifically?
 

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Pistion, rings, sleave scoring, ect....
You could have a small engine shop verify what's going on and quote you a repair cost. Being a 2009 model you may not want to spend the cash on a 11 yr old machine.
 
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