CV740 27hp bogs severely under average load

[VegetiveSteam]

OK, thanks. As it would happen, I currently have both rocker covers off right now. I'll check that in the morning and report back. To be honest thiugh, if this would be even just a little bit off I'd expect some sort of interference with the pistons. No?

There is quite a bit of clearance. I don't think I've ever seen a valve on a Command twin get smacked by the piston.

 

[Turbodriven]

Have you pulled the valve covers and checked the valve lift? Just pulling them and looking at the valves will not tell you anything you have to turn the engine over and watch the valves move. they should move about the same amount.

Yep. Line 32 and 33 of my 'checklist'. All four valves open and close the same amount (+/-0. 2mm). Measured with a straight edge running over the valve cover mating surface on the head (as a baseline for each measurement).

 

[VegetiveSteam]

Something I forgot to ask. Does the engine appear to run fine with no load? Any signs of fuel mist blowing back out of the carb?

 

[Turbodriven]

Something I forgot to ask. Does the engine appear to run fine with no load? Any signs of fuel mist blowing back out of the carb?

Honesty, she starts easy, revs easy, and to my untrained ears sounds fine with no load. It sounds like every other lawn mower I've ever owned. Again, untrained ears. But I digress.

When I push the sticks forward after engaging the pto it's just like someone flips a switch and she falls on her face.

That said... after running I have pulled the intake hose right away and never noticed any fuel build up on any of the pipes. I haven't had my hand over the the intake while idling yet because frankly I wouldn't know what to feel for. But I'll pay attention for excessive fuel misting.

 

[Turbodriven]

Following up on the valve timing check. At TDC exhaust stroke (on both cylinders), the valves teeter right at exactly TDC. I'm going on a limb and saying it's not my issue.

The more I dig in, the more this motor is proving to me that it's healthy. Ugh. Is there any chance this is an external problem? It's not my spindles dragging for sure, I've checked those, but maybe my hyro's are pulling too much drag?? I don't know much about that system or how to check it. And then there is always the carbon fouled #1 thing. If it was an external drag pulling the motor back I'd think both cylinders would be affected? I'm about to set this whole thing on fire at this point.

 

[VegetiveSteam]

Following up on the valve timing check. At TDC exhaust stroke (on both cylinders), the valves teeter right at exactly TDC. I'm going on a limb and saying it's not my issue.

The more I dig in, the more this motor is proving to me that it's healthy. Ugh. Is there any chance this is an external problem? It's not my spindles dragging for sure, I've checked those, but maybe my hyro's are pulling too much drag?? I don't know much about that system or how to check it. And then there is always the carbon fouled #1 thing. If it was an external drag pulling the motor back I'd think both cylinders would be affected? I'm about to set this whole thing on fire at this point.

Okay what do we know? Compression is good. Ignition and valve timing are good. Carb is good. Governor is working as it should as proven by your string. So that tells us that the engine is trying to provide more RPMs by going to wide open throttle but won't speed up. Too much external load is a possibility.

And just to verify, when you did the ignition update you used kit # 25 707 03-S. Correct?

 

[Turbodriven]

Okay what do we know? Compression is good. Ignition and valve timing are good. Carb is good. Governor is working as it should as proven by your string. So that tells us that the engine is trying to provide more RPMs by going to wide open throttle but won't speed up. Too much external load is a possibility.

And just to verify, when you did the ignition update you used kit # 25 707 03-S. Correct?

Correct.

So the big question is how to test that hydro system? Or instead, what would cause a hydro system to have excessive load? If that's even possible? Fluid level is good and looks clean but it has a massive filter that I haven't changed. A clogged filter can't be an issue though, as it should have a bypass valve.

When I bought the mower it came with a 5 rib belt that was missing 2 ribs. So when I had the belt off to change it, I hand spun both hydro pumps and they felt fine (not overly stiff).

Another thing to note is that I'm pretty sure the parking brake is functioning correctly. I'm certain I checked this before but I'll release the hydro locks and make sure the mower rolls easy with the brake off to be sure.

 

[VegetiveSteam]

I'm an engine guy so I'm no help with the hydros but were you able to look for any fuel mist blowing back out of the carb? And is the problem only with the blades engaged?

 

[Turbodriven]

I'm an engine guy so I'm no help with the hydros but were you able to look for any fuel mist blowing back out of the carb? And is the problem only with the blades engaged?

No, valve covers are still off. I'm kind of tired of disassembling this thing and then putting it back together so I took a break today and cleaned up my gas leaf blower instead. I will though. And you're talking about just at high idle with the intake hoses off? What does that indicate if there is?

In regards to the second question. It feels like a combined load thing. The combined load of the blades and the hydros cause the issue.
So for example.
Sticks forward, blades engaged, I have a problem and shes at 1700rpms on flat ground.
Sticks at neutral (mower sitting still), blades engaged, and rpms go back to normal (3300+ rpms).
Sticks forward, blades disengaged and the rpms dip, but not as severe. It'll sit at 2500rpms instead of 1700 on flat ground for example.
The hydros are defininately pulling more average load than the triple blades given these behaviors, which may be completely normal? This is my first zero turn so I can't say.

Something to note, when I say "flat ground" I mean not going up hills. A lot of my property is on a mild slope which I mow sideways (think right or left wheel on the downhill). And I have noticed the problem is slightly less severe when I mow my front yard which is truly flat. As I understand, these Y intake CV Kohlers don't like operating sideways, with gravity and such. It's not my problem per se, but I'm sure it's not helping things.

 

[VegetiveSteam]

I'm trying to figure out how to type this that it makes sense. What I am looking for is an exhaust restriction. I know your spreadsheet mentioned checking that but it may need to be looked at a little deeper. If there is restriction it builds up back pressure and can cause fuel to mist back out of the carb. With no load the engine can reach full RPMs with the throttle plate barely cracked off the idle stop. In that position there isn't a large amount of exhaust to try and get rid of so there may not be any mist blow back. You can try over speeding the engine momentarily 5 or 6 hundred RPMs by hand grabbing the governor lever and look for mist blow back. These engines will easily run over 4000 RPMs with no danger of harming the engine. They hydraulic lifters will begin to float if the RPMs get excessive and that will cause the engine to start cutting out and limit the RPMs. It's sort of an unintended benefit of hydraulic lifters on this engine that won't let it destroy itself from over speeding.

Depending on how the engine is mounted in the equipment it might be easier to just loosen the exhaust at the heads and see if that helps how it runs. It doesn't take much movement of the exhaust manifold away from the heads to notice a difference if there is a restriction in the exhaust.