CV740 27hp bogs severely under average load

[Turbodriven]

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.

 

[mechanic mark]

Kohler CV740 loses power under load

www.lawnsite.com

Found this information above, let us know, thanks Mark

Free Kohler Service Manual Downloads - OPEengines.com

Listed below are Kohler engine service repair manual in Adobe PDF format that you can download for free. Below we have provided a link to these manuals which can also be download. Click on your engine listed below to download. These service manuals provide general information, adjustment...

www.kohler-engine-parts.opeengines.com

Free Kohler Service Manual Downloads - OPEengines.com

Listed below are Kohler engine service repair manual in Adobe PDF format that you can download for free. Below we have provided a link to these manuals which can also be download. Click on your engine listed below to download. These service manuals provide general information, adjustment...

www.kohler-engine-parts.opeengines.com

Locate your engine above & see Troubleshooting Section.

 

[Turbodriven]

Kohler CV740 loses power under load

www.lawnsite.com

Found this information above, let us know, thanks Mark

Thank you for the idea. In his thread it appears as if he had the wrong flywheel which put him out of time. Although I'm certainly under the belief this feels like a timing issue, I don't think I have the wrong flywheel. When I upgraded to the MDI ignition system, I did a lot of research, and it comes in two flavors. One with just the coils and one with coils and a flywheel (to convert ASAM systems). I looked at my flywheel, and pictures of the one that comes in that full conversion kit, and they are the same (in regards to timing keyway positions at least). Also, in the the thread you posted, my flywheel looks like the corrected marks he used to fix the problem. Not like his original flywheel.

All that being said. Is it near impossible to skip a timing gear on these things? Without opening up the case I can't really check that.

 

[VegetiveSteam]

This first bit has nothing to do with your issue but a little extra info for others possibly looking at this thread for their own issues. There are actually three conversion kits for the Kohler Command twin variable timed ignition systems. There are two kits for converting ASAM ignitions that come with a flywheel and two ignition modules. One kit is for both 22 and 23 hp engines and the other is for 25 hp engines. The third kit is for converting DSAM or DSAI ignition systems to the current MDI system. You should have and probably did use kit # 25 707 03-S kit. So all that should be good.

When you checked the flywheel key did you remove the flywheel?

On a note about jumping time. Valve timing may or may not be your issue and It's not a very common problem but a Command twin can get out of valve time easier than you might think. Especially if the engine has ever been over heated. The gear on the crankshaft is a pressed on gear with no key. If the engine gets hot enough, the crankshaft gear can heat up and expand letting it become loose on the crankshaft causing the crankshaft to turn inside of it. The gear doesn't move. The crankshaft does. If you open up the engine, the timing marks will still be lined up because that relationship didn't change, but now if the crankshaft did turn inside the gear it will cause the pistons to be out of time with the valves. The only way to check if valve timing is off on a Command twin is to check valve overlap.

 

[Turbodriven]

The only way to check if valve timing is off on a Command twin is to check valve overlap.

Can you elaborate... or point me to a source that references how to do this?

 

[VegetiveSteam]

Can you elaborate... or point me to a source that references how to do this?

Sure. Can you answer me one question first please? Did you remove the flywheel to check the flywheel key?

 

[Turbodriven]

Sure. Can you answer me one question first please? Did you remove the flywheel to check the flywheel key?

Oh sorry. Yes, I did. Checked the magnets too.

 

[VegetiveSteam]

Click on the link attached below. It will take you to another thread about no timing mark. Once there, go to post #10. I posted a process there. There is also a video attached there showing what valve overlap should look like.

A quick description would be, take both spark plugs out so you can turn the engine over by hand easily. Pick which ever side has the best access to be able to remove the rocker cover. Remove the rocker cover. Rotate the engine until you get the piston at top dead center exhaust stroke. Use wooden dowel that will fit into the spark plug hole so you can feel where the piston is. Just be sure it's long enough that it can't fall down inside the cylinder.

At this time in the cycle the exhaust stroke has just finished and the next stroke is the intake stroke. You will be right between those two strokes. At this point both valves should be open. They aren't open much but they should both be open. If you can rotate the flywheel back and forth about an inch or two clockwise then an inch or two counter clockwise you should see the rocker arms doing a teeter totter. That's valve over lap. If you get that situation of valve over lap with the piston at any other point in the cycle besides TDC exhaust stroke, the engine is out of valve time.

Kohler xt675-2047 NO MARK crankshaft

Hi everyone, I have a problem because when I was removing the oil pan, the camshaft in the Kohler xt675-2047 engine from the Viking lawn mower popped out. The worst thing about it all is that there is no mark on the gear that is mounted on the crankshaft (it is fixed in place, it is not...

www.lawnmowerforum.com

 

[Turbodriven]

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?

Edit : I guess if it was off enough the piston would be heading back down the cylinder and no interference.

 

[hlw49]

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.