CV740 27hp bogs severely under average load

[Turbodriven]

I've taken the exhaust off a few times now. It's not hard. It'll be loud but I'll try running it without to see what happens. Previously I blew through each exhaust port with (sealed) compressed air. #1 wasn't "holding pressure" different than #2 or anything but the testing method did seem pretty un-scientific at the time because my compressor wasn't filling that whole muffler in any quick order.

The more I think about it "scientifically", the more I think that it's the only thing that makes sense really though. Assuming a carbon fouled #1 isn't just some inherent design issue with this motor when you run it at low rpms under load for 5-10min (because the motor is being held back from some external issue).

If it's not a design issue, then we have to look at all the possible (generic) causes of carbon fouling on only 1 cylinder. It has to be one of three things. Too much fuel, too much oil, or not enough air. That's really all it could be.
1.We can eliminate too much fuel because the fuel/air atomizes at the single carb on this motor and gets put into both cylinders equally straight through the intake valves (both 1 and 2 intake valves were tested and they operate the same). If it was a too much fuel issue it would affect both cylinders.
2. It can't be oil because the leakdown test was passing, I'm not burning large amounts of oil, the head gaskets are new, and the valve seals were holding back gas (and therefore oil from the heads too) when I tested the valves. So there is nowhere for the oil to come from. Granted some oil is probably leaking past average condition rings, but not just on cylinder 1. That would be happening on both 1 and 2.
3. Literally the only thing (in my mind) that this could be, is that on the exhaust stroke, not all the un-burnt fuel on #1 is being allowed to exit. Creating a rich condition on the next intake stroke. And we know that the exhaust valve opens the same as #2 (again, checked cold). So this problem wouldn't be at the cylinder head given that evidence.

It's possible that when the motor gets hot the valves are acting differently for some reason. Or maybe the hydraulic lifters are not operating properly under load? It seemed to have fresh oil when I bought it so I didn't do an oil change. Perhaps I should. I know oil viscosity affects how hydraulic lifters perform (although I'm not an expert on hydraulic lifters either). That said, improper oil would affect all the lifters equally. So it sort of rules itself out.

Sorry for the long post, it's mostly me putting my thoughts on paper. I'll check the exhaust and report back. Thank you for all your help so far!

 

[VegetiveSteam]

I know you mentioned that all the valves were opening the same distance and sorry if I missed it but, how much are they moving? 3/8" or more?

And with a single barrel carb feeding two cylinders, one spark plug on a Command twin is typically just a slight bit darker than the other. The difference doesn't normally jump out at you but it is noticeable when you lay them side by side. So #1s being fouled is letting us know something is not right.

 

[VegetiveSteam]

Has it ever run right for you since you bought it?

 

[Turbodriven]

Has it ever run right for you since you bought it?

No, I bought it about a month ago with a slew of problems. Mostly electrical issues which I sorted out. It was completely missing a starter relay for example. And wires were cut and/or not hooked up to the ignition switch (ad said it needed a new switch, but it did not)

But no, it always had this rich/motor bogging issue for me.

I bought it from an old guys son who didn't know anything about it. His dad came out for a few seconds at the end and just in passing mentioned that he parked it a year ago because of a leaking crank seal. He had maybe 10 mowers scattered around his lawn. Not one drop of oil has leaked past the crank seal on this since I owned it though. And he didn't seem superbly mechanical. So maybe he was confused about a different mower. Curious detail though.

I know you mentioned that all the valves were opening the same distance and sorry if I missed it but, how much are they moving? 3/8" or more?

It's tricky to get a measurement, but both intake valves are opening a total of 7mm. Exhaust appears to be the same.

 

[Turbodriven]

I know you mentioned that all the valves were opening the same distance and sorry if I missed it but, how much are they moving? 3/8" or more?

I just took a look in the Kohler manual. It appears as if 7mm is a bit out of spec? Unless this needs to be done on a hot engine (hydro lifters freshly pumped up)? The motor has been cold and sitting for a few days.

Again though, #1 and #2 are the same amount out of spec. So it wouldn't explain why only #1 is rich??

 

[VegetiveSteam]

Retiring two years ago, I worked 27 years for a Kohler distributor doing this exact thing for about 9 months out of the year. We dealt mostly with Kohler authorized dealers helping them with engine troubleshooting, parts help and warranty. That was a little easier than this because it was all done on the telephone. A tech would call in and we’d discuss a few things to check or try. If they still had trouble they’d call back and we’d try to think of other things. Sometimes we found a solution with one call and sometimes it took multiple calls but we normally would find the issue.

The other 3 months of the year were spent conducting in person 4-day factory required schools for new Kohler dealers and update seminars for current Kohler dealers.

I also spent 14 years on the EETC 4-cycle test committee. While I feel I have a good bit of knowledge, mostly about Kohler engines, I admit not doing it everyday has dulled my skills some. Things that would just come right off the top of my head aren’t second nature any longer. I had a huge amount of reference material loaded with notes I’d made over the years. Thinking I wouldn’t have much need for it anymore I threw most of it away about a year ago. I threw away over 25 years of factory update books with notes in each one from our yearly factory training. I would love to that info back.

I think that as far as the engine goes you’ve covered just about everything there is to cover other than maybe a little more checking on possible exhaust restriction.

It reminds me of what my boss used to say when I’d ask him his opinion or to help me understand what I might be missing. He was a great guy and spent over 40 years teaching Kohler engines. He forgot more about Kohler K-series and Magnum engines than I ever knew. He was funny with a great sense of humor. I’d ask him for advice, and I’d say, we’ve, (meaning me and the technician), tried everything. He always like to reply, “you haven’t tried everything, or you would have found the problem.” I learned quickly to change my verbiage and started saying, “we’ve tried everything we can think of.

That leads me to the point of my rant. What are we missing? It was nice when I was still working. Three of us shared an office so it was easy to bounce ideas off each other. Usually someone would come up with something that might have been missed. If we were still lost, one of us would call the factory and run it past one of their techs.

I feel if the exhaust restriction turns up negative, it could be a hydro load issue but I just don't know. You’ll need to find someone smarter than me for testing that.

Once it's back together running again, if it's possible, post a video of it acting up. Maybe even one of it sitting running with no load at idle and also full throttle. Who knows. Maybe someone will hear something.

 

[Turbodriven]

I feel if the exhaust restriction turns up negative, it could be a hydro load issue but I just don't know. You’ll need to find someone smarter than me for testing that.

Once it's back together running again, if it's possible, post a video of it acting up. Maybe even one of it sitting running with no load at idle and also full throttle. Who knows. Maybe someone will hear something.

If it's the exhaust, I'll throw a party I swear. Fingers crossed.

If not, I'll take a video. Or two. One of it starting cold and throttling up and down with no load. And one mowing showing the precise issue on the tach.

 

[Turbodriven]

Well, it's not the exhaust.
Interesting note, it runs like absolute dog sh@t without the muffler attached. Still dropping rpms though. With the added poor running, it was almost un-driveable now.

Also interesting, is the residue left from each cylinder. I took pics. The exhaust from the heads (muffler off) dumps onto the motor mount plate which is normally gloss black. Cylinder 1 is significantly blacker and spread wider. There is something going on in this engine.

At this point I just think this motor needs to be pulled apart piece by piece and inspected. Valves, crank case, everything. Whatever is causing this should be pretty obvious once I find it I would think. I'm out of external ideas though. Nothing from the outside is giving it away for sure.

I'll put the muffler back on tomorrow and shoot the two videos still. See if that presents any evidence I'm incapable of seeing.

 

[VegetiveSteam]

Maybe tearing into it is the next step but to me, the things you've checked such as, compression and valve timing on top of new head gaskets says to me it's not internal. But it wouldn't be the first time I was wrong. Your valves may be opening a bit under spec but I don't think it's enough to be an issue.

After you get it back together, try running it on one cylinder at a time and see if it runs the same on both sides. I know others will disagree and say they do it all the time with no issues but my recommendation, (actually Kohler's recommendation right in their service manual) is to not pull a plug wire while the engine is running or run the engine with a plug wire dangling firing to the atmosphere. Pull the plug lead and ground it to the block with a spark tester or some other way. Those leads need to be grounded. Then start the engine. Not doing it this way probably won't damage the ignition module immediately but there is a good chance if you pull the plug wire while running or let it fire ungrounded you've shortened the life of the ignition module.

Since there is normally no immediate failure people think it doesn't hurt anything. But when the customer returns in the next year or two needing a new ignition module, the tech who pulled the lead while running could be the reason they need it and it probably should have lasted a lifetime.

I didn't watch the video from an earlier post but I think you said you feel the flywheel is the correct flywheel? Not knowing the history or what the previous owner might have done to it doesn't help you any either. There's possibly more to it than they shared with you.

 

[Turbodriven]

I didn't watch the video from an earlier post but I think you said you feel the flywheel is the correct flywheel? Not knowing the history or what the previous owner might have done to it doesn't help you any either. There's possibly more to it than they shared with you.

Yeah I'm almost certain it's correct. I base this on the following: the flywheel that comes with the 24-755-308-S MDI conversion kit has 8 gear teeth between the keyway and the start of the magnet. So does my flywheel. It's a little different in overall design but the timing degree is the same. And my flywheel was caked with grass/dirt on the internal magnets when I pulled it. Somone put hundreds of hours on it for sure prior to me owning it. I'm guessing hundreds of hours that the motor was healthy?