CV740 27hp bogs severely under average load

[Turbodriven]

Check a shop manual for proper valve adjustment. I think valves aren't supposed to be tdc when adjusted. I think there is a compression relief that holds the exhaust valve open a bit.

This motor has no compression release. And hydraulic lifters with no valve adjustment.

 

[donslawns]

Can anyone help here?

I'm absolutely baffled by this issue. I am now 100% out of ideas. The problem presents itself in two ways.

1. Within the first few moments of average load mowing, the motor RPMs dip significantly (about 5-10 seconds after engaging everything ). The greater the load, the more the RPMs dip. I hooked up at tachometer and it shows 1200 at low idle, 3600 "high idle", and during mowing it will usually sit right around 1700 RPMs depending on load (barely enough to mow). If it's a downhill, it'll go to 2500 or so, and small uphills dip to the point of basically being at low idle speed. If at any point I pull back the sticks to a stop (blades engaged), rpms will slowly pull back up to 3300+ RPMs (in 3-5 seconds). Push the stick forward and it dips back into the 1700 range.
2. Using clean plugs, cylinder #1 plug is always turns sooty black (carbon fouled) after a ten minute mow. Cylinder #2 is white to very light brown (varies). But never rich like #1.

I've put together a spreadsheet to track this problem. Just because after checking EVERYTHING I wanted to make sure I didn't miss anything. I know it's a lot, but it will show that I've tested all the typical problems.
The mower is a 2005 Gravely 260z (zero turn) that I bought a month ago for cheap.
I'm completely at my end here and would be happy for any experienced ideas.

View attachment 66771

90% of the time when someone brings a mower in and they say that they have low power, they are running on one cylinder and don't know it because the exhaust doesn't sound that much different to the average person. Pull one spark plug wire off at a time. The engine should run on one cylinder and if you kill the engine by removing a plug wire then you know that the other cylinder is not producing power. You can also use an infrared to see if both exhaust pipes are hot, a cold pipe is a dead cylinder. If a dead cylinder is the problem you can work from there.

 

[donens2018]

From working with the Command series twins, my experience is that of faulty magnetos (coils). Also since Kohler used so many versions of coils, makes it difficult. The latest coils offered by Kohlers states to replace as a pair, primarily to avoid mixing up different versions. Sounds like you have coils failing. You may also check the kill wire, as Kohler for one version had a diode wired into the harness due to back feed. The newest coils have the diode built into the module.
Have you run engine with inline spark testers on each coil. Check for cylinder spark differences especially when it starts loosing power. Also check the wiring harness. I'm seen too many wiring harnesses with evidence of mice chewing. They like the insulation.

 

[corvette 1]

Can anyone help here?

I'm absolutely baffled by this issue. I am now 100% out of ideas. The problem presents itself in two ways.

1. Within the first few moments of average load mowing, the motor RPMs dip significantly (about 5-10 seconds after engaging everything ). The greater the load, the more the RPMs dip. I hooked up at tachometer and it shows 1200 at low idle, 3600 "high idle", and during mowing it will usually sit right around 1700 RPMs depending on load (barely enough to mow). If it's a downhill, it'll go to 2500 or so, and small uphills dip to the point of basically being at low idle speed. If at any point I pull back the sticks to a stop (blades engaged), rpms will slowly pull back up to 3300+ RPMs (in 3-5 seconds). Push the stick forward and it dips back into the 1700 range.
2. Using clean plugs, cylinder #1 plug is always turns sooty black (carbon fouled) after a ten minute mow. Cylinder #2 is white to very light brown (varies). But never rich like #1.

I've put together a spreadsheet to track this problem. Just because after checking EVERYTHING I wanted to make sure I didn't miss anything. I know it's a lot, but it will show that I've tested all the typical problems.
The mower is a 2005 Gravely 260z (zero turn) that I bought a month ago for cheap.
I'm completely at my end here and would be happy for any experienced ideas.

View attachment 66771

New air cleaner, carb cleaner & spark plug.

 

[moseemo54]

This motor has no compression release. And hydraulic lifters with no valve adjustment.

Had similar symptoms with my exmark Kohler, I believe it's a CH 745. Seemed like it was starving for fuel. Finally noticed the original fuel line on the suction side of the fuel pump was partially collapsing under load and restricting the flow. I had an experienced professional mechanic trouble shooting it with me and before we found it, had replaced the fuel filter and fuel pump. Might be something worth checking.

 

[Cajun power]

leak down test...start there.

and listen closely ..it could be from multiple places (head gasket failure, cracked or warped head, valves). this will establish and point you to where leaks might be coming from if you have leaks. (see youtube for numerous methods and standard tips. always do this on top dead center, one cylinder at a time)

also look for any blown gaskets in the intake manifold where it mates to the cylinder head. usually this will cause a very lean condition, but if the intake gaskets are big time blown, this messes up the fuel air mix and can cause alsoloss of power....but it's usually a very high revving engine and super hot even at idle! if the intake manifolds are warped, and or the gaskets have failed big time, then you simply don't get enough fuel or air..

also...make sure you don't have something wrapped around the blades, blade spindles, tensioner pulley, and or pto clutch. check those belts and make sure nothing is binding up the blades. (engine OFF when checking of course!)

is the fuel pump operating normally? (ENGINE OFF: remove the fuel line from the carb and crank the engine and let it run...make sure you have a catch can for gas and in a safe position...and a fire extinguisher at the ready just in case....fuel flow from fuel pump should be strong and steady.

when was the last time that the carb has been cleaned? specifically the main jet...at idle debris will allow the engine to run and sound normal...at a higher rpm fuel demand, debris in the carb can cause loss of power.

 

[doug9694]

Can anyone help here?

I'm absolutely baffled by this issue. I am now 100% out of ideas. The problem presents itself in two ways.

1. Within the first few moments of average load mowing, the motor RPMs dip significantly (about 5-10 seconds after engaging everything ). The greater the load, the more the RPMs dip. I hooked up at tachometer and it shows 1200 at low idle, 3600 "high idle", and during mowing it will usually sit right around 1700 RPMs depending on load (barely enough to mow). If it's a downhill, it'll go to 2500 or so, and small uphills dip to the point of basically being at low idle speed. If at any point I pull back the sticks to a stop (blades engaged), rpms will slowly pull back up to 3300+ RPMs (in 3-5 seconds). Push the stick forward and it dips back into the 1700 range.
2. Using clean plugs, cylinder #1 plug is always turns sooty black (carbon fouled) after a ten minute mow. Cylinder #2 is white to very light brown (varies). But never rich like #1.

I've put together a spreadsheet to track this problem. Just because after checking EVERYTHING I wanted to make sure I didn't miss anything. I know it's a lot, but it will show that I've tested all the typical problems.
The mower is a 2005 Gravely 260z (zero turn) that I bought a month ago for cheap.
I'm completely at my end here and would be happy for any experienced ideas.

View attachment 66771

 

[riceski@gmail.com]

Can anyone help here?

I'm absolutely baffled by this issue. I am now 100% out of ideas. The problem presents itself in two ways.

1. Within the first few moments of average load mowing, the motor RPMs dip significantly (about 5-10 seconds after engaging everything ). The greater the load, the more the RPMs dip. I hooked up at tachometer and it shows 1200 at low idle, 3600 "high idle", and during mowing it will usually sit right around 1700 RPMs depending on load (barely enough to mow). If it's a downhill, it'll go to 2500 or so, and small uphills dip to the point of basically being at low idle speed. If at any point I pull back the sticks to a stop (blades engaged), rpms will slowly pull back up to 3300+ RPMs (in 3-5 seconds). Push the stick forward and it dips back into the 1700 range.
2. Using clean plugs, cylinder #1 plug is always turns sooty black (carbon fouled) after a ten minute mow. Cylinder #2 is white to very light brown (varies). But never rich like #1.

I've put together a spreadsheet to track this problem. Just because after checking EVERYTHING I wanted to make sure I didn't miss anything. I know it's a lot, but it will show that I've tested all the typical problems.
The mower is a 2005 Gravely 260z (zero turn) that I bought a month ago for cheap.
I'm completely at my end here and would be happy for any experienced ideas.

View attachment 66771

Try this and I have found this to be an absolute -- charge the battery to the fullest - or even put a different good battery in the mower - have found IF the battery doesn't deliver enough amperage it can cause what you are saying to happen. If the alternator isn't putting out enough to run everything correctly - these symptoms can come about. Good luck with it.

 

[doug9694]

The only thing I can come up with is maybe a leaky porous casting around the intake valve or the intake manifold itself.
Carefully see if one cylinder is running much cooler then the other. Or use an infrared thermometer.
The cool cylinder is most likely where the issue is.
Reading more comments another prob. may be a hydraulic lifter collapsed after the cold thick oil thins when warm.
Also do the spark plug wire pull test. That should tell which is bad.

 

[Sockmonkey]

Can anyone help here?

I'm absolutely baffled by this issue. I am now 100% out of ideas. The problem presents itself in two ways.

1. Within the first few moments of average load mowing, the motor RPMs dip significantly (about 5-10 seconds after engaging everything ). The greater the load, the more the RPMs dip. I hooked up at tachometer and it shows 1200 at low idle, 3600 "high idle", and during mowing it will usually sit right around 1700 RPMs depending on load (barely enough to mow). If it's a downhill, it'll go to 2500 or so, and small uphills dip to the point of basically being at low idle speed. If at any point I pull back the sticks to a stop (blades engaged), rpms will slowly pull back up to 3300+ RPMs (in 3-5 seconds). Push the stick forward and it dips back into the 1700 range.
2. Using clean plugs, cylinder #1 plug is always turns sooty black (carbon fouled) after a ten minute mow. Cylinder #2 is white to very light brown (varies). But never rich like #1.

I've put together a spreadsheet to track this problem. Just because after checking EVERYTHING I wanted to make sure I didn't miss anything. I know it's a lot, but it will show that I've tested all the typical problems.
The mower is a 2005 Gravely 260z (zero turn) that I bought a month ago for cheap.
I'm completely at my end here and would be happy for any experienced ideas.

View attachment 66771