CV740 27hp bogs severely under average load

[Turbodriven]

Let me ask a silly and probably useless question but, do you still have the spark advance module you took off this engine? If so, what's the number on it?

We talked about it in a different thread. I had the DSAM system apparently. The box was 24 584 27 and the coils were 24 584 15. I assume now they were all working fine?

 

[Turbodriven]

I was in the shop this morning and took a better look at my lifters (and got a better pic). They are all perfectly smooth except #1 intake (top left in pic1 with matching cam lobe the one nearest to it). You can feel that wear on the lifter with your finger.
A. would you be concerned about this? and..
B. if so, can I replace a just a single lifter or are we talking a full $500 crank/cam/lifter deal again? In your opinion?

 

[VegetiveSteam]

We talked about it in a different thread. I had the DSAM system apparently. The box was 24 584 27 and the coils were 24 584 15. I assume now they were all working fine

And I know we talked about the flywheel too but since you're dealing with something elusive I thought it wouldn't hurt to know for sure you had DSAM. And you did. I'm trying to look under every stone.

 

[VegetiveSteam]

I was in the shop this morning and took a better look at my lifters (and got a better pic). They are all perfectly smooth except #1 intake (top left in pic1 with matching cam lobe the one nearest to it). You can feel that wear on the lifter with your finger.
A. would you be concerned about this? and..
B. if so, can I replace a just a single lifter or are we talking a full $500 crank/cam/lifter deal again? In your opinion?

You can replace just one lifter. They used to come with a little tube of grease to put on the cam side. I assume they still do. Put a couple of drops of oil on the push rod socket side and a drop in the hole. Then run the engine at 1500 RPMs for 5 minutes.
The lifters normally rotate but not always. That straight line wear isn't all that uncommon and normally doesn't cause an issue.

 

[Lawnman23]

The lifters normally rotate but not always. That straight line wear isn't all that uncommon and normally doesn't cause an issue.

What would cause that much of a grove on just the one intake lifter and nothing on the others? Usually its a lifter eating a cam lobe not visa-versa no?

 

[gregjo1948]

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

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.

 

[STEVES]

worn valve guide/seal sucking oil / should of removed valves with head off, usually can do by hand pushing spring down /

 

[JAZ]

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

Don't really think I will be of much if any help, but my Troy built 42 " did the same. Number 40 on your list said belts new or good. I replaced the belt on it and seems to have corrected the problem. Belt was good but stretched.

 

[STEVES]

if belts, are they on the correct side of guide?

 

[Turbodriven]

worn valve guide/seal sucking oil / should of removed valves with head off, usually can do by hand pushing spring down /

Line 30 and 31 of my OP checklist sort of verified that at least the intake seal isn't leaking (and this motor has no seal on the exhaust valve by design). But I removed the #1 valves yesterday and they don't seem loose in the guides. Not tight, but not loose either. Guides are positioned vertically in the heads correctly too and haven't slipped. And leak down confirms that the exhaust valve is closing properly.

At this point I just think my motor is possessed by a demon. Nothing but a slightly out of spec cam is the only thing I see even remotely 'wrong'.