I bought a used John Deere rider earlier this summer from a private party. 38" deck, Kohler Command 13 engine, hydro. It starts good and sounds good, no miss, no knocks, no smoke, doesn't burn oil.

The problem is that it doesn't seem to have the power that it should. When I first start it, it doesn't run up to the governor; I'm guessing the RPM is 1/2 - 3/4 what full throttle should be. When I engage the blade, it almost dies. I have taken the deck belt off and the blades and pulleys turn free. After it runs a half hour or so it will run up to the governor speed but pulls down easily in longer grass or with higher ground speed. I mow the lawn with it but it takes longer than it should and probably doesn't cut as well as it would if RPM was higher.

1 Oil & filter were changed in early July. Oil is still clean and at full line
2 There is no difference in running speed with air filter on/off
3 I don't have a manual for carb adjustment. One of the screw heads for adjustment is damaged so a screwdriver won't work--looks like somebody tried to turn it out and it was stuck. The needle only turns about a half turn and doesn't make a diff in running speed and there's no resistance, like it isn't really turning the screw.
4 Engine doesn't idle. It goes from high speed to off.
5 Engine starts with little or no choking.
6 I have run Seafoam in several tanks of gas.
7 Spraying carb cleaner on the carb while running makes no diff in RPM or engine sound, so it apparently has no leaks.

As I write this I'm thinking that the high speed adjustment is (stuck) closed and that the low speed is opened too far. Does this sound right? I think getting that adjustment needle freed up is the first step to take. If that needle has been turned in too tight and is stuck, what are the chances the seat is damaged? Any suggestions on getting a stuck needle out with out breaking something?

First lets make sure you have the grass screen clean, gas cap vented, fuel filter changed, fuel line connection checked, and the air cleaner on and seated properly. You should probably do a compression test before doing anything else.

Next I'd check the fuel pressure from the fuel pump.
One more little culprit is the shutdown solenoid. You might or might not have one.

Carb setting and adjustments will depend on what carb you have.
No power: there is no high speed adjustment, instead a fixed high speed jet. Make sure the governor is hooked up.
It sounds like you have a limit cap on the idle fuel adjusting screw. If your not getting any change when adjusting, then its possible your idle speed needs to be set, then go back to idle mixture(if you have (one). Since you have no power and you checked out the above, you should probably go right to a carb cleaning. Make sure to get all circuits and high speed jet.
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I would also add to check the throttle linkage, starting at the cable and all the way through to the governor links to confirm that the throttle moves freely from open to close. Also check the tiny springs connecting governor links. I've found many that were so plugged up with grass and dust that they would barely move. Just because the lever moves freely doesn't meant the actual throttle is moving.

Great advice Macgyver55!

Try a new spark plug.

I did put on a new fuel filter. I had also checked the governor & throttle linkage for free travel. Everything moves freely, choke comes on at the correct throttle position, etc. Moving the governor linkage doesn't do anything until after it has run a while, as said previously, when it sounds like it's running at full throttle. Then moving the governor arm lets it over-rev. I don't have a compression tester but will check it with my thumb tonight.

No obstructions in the air cleaner system.

Since it sometimes starts cold without choking, I wasn't suspecting low fuel deliver or bad pump. Plus, I'd think that when it's first started there is enough fuel in the bowl to let it run normally for a while, which it doesn't.

"It sounds like you have a limit cap on the idle fuel adjusting screw."
ST, can you explain that. I don't know what a limit cap is or what to do about it.

Mac, I didn't consider a spark plug because there is no miss, but stranger things have happened. I'll try that too.

I do appreciate the responses.

A friend of mine had similar problems and it turned out to be the spark plug. Pretty cheap to try. Good luck.

Sorry Maverick, I referred to you as Mac in a previous post. I was pressed for time and didn't check the name close enough.

I replaced the spark plug but it made no difference. It was hard to check the compression with my finger because the hole is way recessed and my finger barely reached, especially while trying to hold the clutch in and turning the key, but it felt like there was plenty of compression.

Surface Tension- can you give me any more hints about the locking cap you mentioned before I tear the carb apart?

Before you tear the carb apart make sure you take real good digital pics of everything. The governor is the one that is always hard to figure out how it goes back together.

Good idea. Thanks

Its a limiter cap. Meant so that you can't go past the recommended setting and like I said it depends on which carb you have. Go through my above procedures. Your finger is not a good indicator for compression. Your not the first Dear John owner that has gone though this. Don't over look the shutdown solenoid(if you have one).

Something else that might be causing this, do you have an engine stop brake?

I'm pretty sure there isn't an engine stop brake. I'm not sure what a shutdown solenoid is. I'm guessing it shuts off the fuel (?). There's nothing between the tank and carb except the filter and manual shutoff valve. It's apparently gravity fed. I don't see any wires going to the carb, if that's where the solenoid might be.

Limiter cap-- does that mean there isn't a way to override it?

After thinking about it, I don't remember it acting like this when I first got it. I'm wondering if the Seafoam might have broken a chunk of something loose and is plugging a jet. The engine revs way up when I disengage the blades.

I did grease the blade pulley hubs and they turn free. Shortly after I got it I put on new blades, but they are the same part number as what was on there before. I think I'm going to have to pull the carb apart this fall or next spring.

I don't know how much compression it's supposed to have. It blew my finger off the hole and sucked it back in on the downstroke, probably better than on Briggs engines I've done that with in the past. Since it burns no oil, I'd think the rings are working like they should. I was a little surprised how it sucked my finger in. Could that mean a valve isn't opening enough to let gas into the cylinder?

I did some more mowing with it tonight. After it ran for a while it worked well on grass that wasn't too thick. On the thick green damp stuff I had to slow down the ground speed quite a bit.

If it is a Tecumseh's engine there will be a brass nut holding the float bowl on the carburetor. This bolt is a jet and tends to foul or plug easy. Simple to unscrew it and clean all the holes with a wire and carb cleaner. Compression test may not be relevant. A lot of these motors have compression release so you probably cant get a good compression test.

Lets first get it to idle. Clean the carb. Loss of power while cutting is a common JD problem with a finicky deck. Improper deck adjustment, build up of grass/clogged, dull blades, wrong blades and using mulching shoot, and lastly, bad clutch. You said you greased the spindles. With the belt off can you turn the clutch by hand.
What model is this mower?