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Kohler Command Pro 20 driving me crazy

CrazyJ

LawnSite Member
Location
Raleigh
It's on a UTV. It doesn’t want to idle unless I'm screwing with the choke constantly-- any time RPMs drop I have to choke a bit to keep it from cutting off. Also hesitates on giving it too much throttle too quickly. It won't idle to warm up on choke like it use to. Just generally runs like crap when anywhere near idle speed.

Over the past few month or two, I have heard several metallic clanking sounds coming from behind me while driving the UTV. They are short and stop immediately. I haven't been able to determine if they are coming from the motor, but they could be.

It's running really rich after I've done everything. Also spits gas up the carb throat every time accelerated quickly. Sometimes spits a lot of gas up. Sometimes backfires through intake.

It makes a lot of metallic noise when starting (just started this after starting over 100 times), and the starter disengages. I think the metallic noise is coming from the starter itself and not the engine.

Things I've done:

- Checked fuel. It seems to be delivered well by the pump. I've also added a primer bulb for testing to keep it pumped up. And I've tried to hook it up to a aux tank of fresh premium gas. Nothing changes behavior.

- Cleaned carb ... may have smoothed out it surging. I've since bought an entirely new carb, but I still have the same symptoms above.

- Replaced head gaskets. I started this because it was getting hot and I blew air through and felt it escaping around heads. I've since realized this was due bad machining of the exhaust headers (they were really hard to see without pulling heads or engine), which I've since fixed also.

- Replaced both coils and both plugs. I noticed it not sparking when using timing gun. I've since realized that is because I had the clamps backwards a good percentage of the time. I now seem to have great spark when I hook up the clamps correctly. I have two inline spark testers that just arrive via Amazon that have never been installed.

- I've hunted down for an intake manifold leak or carb air leak. Visual inspection. Retorquing bolts. Also spraying all over with cleaner. No luck here.

- I measured the crankcase vacuum and got 4.5 in h20. I still flipped over the breather reed. No change in engine performance.

- I've measured lifter height (crudely). Seems to be about 7.5mm for all valves. I have a hydraulic lifter puller coming today. I'm wondering about sticky valves. When the engine is turning off, I can stare a the valves and see the intake on one side go up and down 2-3 times without the exhaust going up. But this could be due to the crank turning backwards, etc. I don't think this motor has compression release.

- I'm going to check the flywheel key later today, but I don't have much hope here.

Pulling the motor is a bit tricky due to how it's shoehorned in there and the removal of the UTV drive pulleys, etc, so I haven't done that yet to look at the insides.

I feel like such an idiot with this one; clearly I should have had someone else handle this. I hate this motor.
 
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CrazyJ

LawnSite Member
Location
Raleigh
Forgot to mention—

- compression test both cylinders ~135 psi
- leak down test test Good

i took off he flywheel today. The key was intact. One of the internal magnets had come unadhered. This is already my 2nd flywheel due to the magnets becoming unstuck. I guess it’s better I caught it early this time before it destroyed the magnet... I guess. I don’t suppose that could cause these problems? Maybe the noises though? I’ll be giving it a shot tomorrow...

I hate this engine.
 

Creole

LawnSite Member
Location
Virginia
After replacing the carb, does it still only run on choke or is it now spitting fuel like it's getting too much? What kind of carb did you replace it with? Chinese?

I think the issue is it the carb since all of your other test have checked out.

One last thing you could check is the governor. Is that set properly and functioning like it should?
 
OP
C

CrazyJ

LawnSite Member
Location
Raleigh
After replacing the carb, does it still only run on choke or is it now spitting fuel like it's getting too much? What kind of carb did you replace it with? Chinese?

I think the issue is it the carb since all of your other test have checked out.

One last thing you could check is the governor. Is that set properly and functioning like it should?
It seems to run exactly the same with the new carb. Yes, I think Chinese; certainly not Kohler.

I had suspected the governor. It's been readjusted. The governor seems to respond when it's dying, but the governor does exactly what I'd do when it's dying-- give it more gas ... which is kind of what kills it. When I said "hesitates", I may have misspoke. Giving it a lot of gas will kind of spit up the carb and kill the engine. The only thing to do when it's dying is to give it partial choke to revive it.

BTW, I've opened the original carb up no less than 10 times and even re-replaced those crappy o-rings, etc. I've been through every orifice in the original carb. It was sparkling clean to begin with, and it's just as clean now. I used to drive this machine almost every day ... it never sat.
 

Justin Hightower

LawnSite Member
Location
western Ky
Junk carb. Even though you bought a new carb Chinese is junk lol. Either get a OEM carb ($$$) or take your carb to a small engine shop and have it disassembled and cleaned in a ultrasonic cleaner.
 

Creole

LawnSite Member
Location
Virginia
It seems to run exactly the same with the new carb. Yes, I think Chinese; certainly not Kohler.

I had suspected the governor. It's been readjusted. The governor seems to respond when it's dying, but the governor does exactly what I'd do when it's dying-- give it more gas ... which is kind of what kills it. When I said "hesitates", I may have misspoke. Giving it a lot of gas will kind of spit up the carb and kill the engine. The only thing to do when it's dying is to give it partial choke to revive it.

BTW, I've opened the original carb up no less than 10 times and even re-replaced those crappy o-rings, etc. I've been through every orifice in the original carb. It was sparkling clean to begin with, and it's just as clean now. I used to drive this machine almost every day ... it never sat.
If it will only come back to life with the choke on it seems to be that it might be a fuel delivery issue. How is everything fuel related before the carb? Fuel lines good no kinks or obstructions? Fuel filter clogged? Obstruction in tank? Fuel pump working like it should? Is the fuel pump electric or mechanical?

Since you have been through everything on the carb so throughly I would start to lean towards valves, but if your leak down tests came back fine then I would think that the valves would be ok.

If every part of the fuel system checks out then it may be time to open it up and check internal components.
 
OP
C

CrazyJ

LawnSite Member
Location
Raleigh
I had looked into fuel delivery. The mechanical pump driven by the rockers has always seemed strong-- it refills the carb fairly quickly after I remove/install the carb.

I've removed the valve covers for testing and use a fuel bulb in place of the pump. It pumps very freely. No restriction from filter. Same behavior as having the mechanical pump.

I did a couple videos today. Here is one:
https://www.youtube.com/watch?v=breebu8X2xI

You'll see spitting at 0:20

You'll hear it stall and spit up gas when given throttle at 1:50.

I have some other videos that visual show it igniting and blowing out of the carb.

I know I don't have the air cleaner on, the valve covers installed, the governor installed, or a host of other things that could possibly cause issues, but I've tried putting it all together, and it acts the same.

Guys, I'm tempted to get a new carb, as suggested, or have the old one professionally cleaned ... but I just can't believe it's the carb when the brand new one (chinese, I know) acts the exact same as mine.
 

Helger Services

LawnSite Member
Location
Holden, Ma
On our 2010 Exmark Lazer Z has a Command Pro 25hp on it and it is one of the worst motors we have ever run, awful on fuel, burns oil, leaks oil (since 300hrs), fowls plugs every other day and is significantly under powered. We've rebuilt it twice because the rings fail so quickly, granted the motor has 3800hrs on it but its main problems began at 800 and we are now swapping to a Kawi FX921. Photo below is the second time we pulled the engine
 

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