CV740 dies after getting hot....at my wits end on this

[dbrunone]

This has been an ongoing problem for 2-3 years now and I'm completely out of ideas, at my wits end with this damn thing. Unit is a Ferris IS3000Z zero-turn with a Kohler CV740 27hp motor.

Problem: pretty consistently 15-20 mins into mowing my lawn, especially if it is thick and the motor is stressed, the thing will just die. BUT, if I quickly turn off the blade and pull the choke, I can keep it running. Going back to Run will kill it right away. After it does this, it doesnt run right for the rest of the day or sometimes longer. I'm mostly able to get it back to the garage in "full choke" although sometimes it dies doing that too, and I need to crank it a lot to re-start it.

If I can get it re-started in the garage and get the choke to run, it will surge up and down, or sometimes die completely. The infuriating thing is, sometimes (like last week) it will do the whole lawn perfectly with no issues.

Things I've done to try to remedy in the past 6 months:

• Replace ignition modules (incl plug wire) with new, using a kit Kohler recommends which eliminates the spark advance module and goes to a "fixed" timing system (this is the part they direct you to buy when looking up old ignition module numbers)
• New spark plugs
• Checked continuity of all wires going to ignition system
• Checked spark with a spark tester
• New fuel filter
• New fuel pump
• New carburetor
• Checked compression (even while its acting up), I get ~150psi on both cylinders which is what the book recommends
• Took fuel hose off carburetor and cranked it, watching fuel pump rate (looking for clogged lines). Was fine on all tank selectors
• Took off valve covers and watched valves actuate while cranking. Nothing abnormal.
• Shop 2.5 years ago replaced head gasket thinking that was the problem
• Different shop recently blew out all fuel lines with air and cleaned fuel tanks
• Ran a bunch of Seafoam through it in the fuel

It seems every time I replace something, it works great for 2-3 mows, and I think I nailed the issue, then problem comes right back with the same behavior. Sent it to 3 different shops over the past 3 years, they can't figure it out either, some of them say they can't get it to act up.

Hunting goes something like this (this vid is from last year):

Here are the valves:

PLEASE help, I'm about to sledgehammer this thing....

 

[ILENGINE]

Sounds like starving for fuel. Pulling the choke about proves it. Since all the normal parts have been replaced. Just a though next time it starts doing then feel the carb bowl, and see if it is getting hot to the touch. Since everything has been replaced I am wondering if getting heat from exhaust causing fuel to boil in carb bowl.

 

[Hammermechanicman]

Does sound like vapor lock. Check the. Cylinder cooling fins for animal stuff. Check that no exhaust gas leaking near carb. When the engine start surging spray some water on the carb and fuel line to cool them and see if it changes how it runs. Might take some aluminum foil and make a heat shield to put between carb and engine/muffler and see what happens.

 

[StarTech]

Sounds like starving for fuel. Pulling the choke about proves it. Since all the normal parts have been replaced. Just a though next time it starts doing then feel the carb bowl, and see if it is getting hot to the touch. Since everything has been replaced I am wondering if getting heat from exhaust causing fuel to boil in carb bowl.

Or could be like few engines that I saw the last few Springs here where Winter gasoline is boiling in the fuel lines and filter during our hot Spring weather from the exhaust heat. I can actually see it bubbling in the clear filters. The only solution so far has been to insulate the fuel lines. Once Summer gasoline mix start being at the fuel depots the problem went away.

 

[arch252]

I had this happen on a 17hp Kawasaki. I added a brush guard to a JD LX279 and the side plate of the brush guard was redirecting some of the exhaust toward the carb, getting it hot and causing a vapor lock.

 

[dbrunone]

SOLVED!!! After 3 years and over $1500 and several full days of my time thrown at this thing, I finally found the problem. And it is as stupid as you'd think. I even spent a whole day tearing off the heads and replacing head gaskets thinking that might be the issue.

At the suggestion of my father in law's mechanic friend, I ran a temp wire straight from the battery + terminal to the fuel solenoid on the carburetor. BAM, thing fired up instantly and ran perfectly.

Bottom line is, although I measured 12.5V at the solenoid connection point, something is pinched or frayed somewhere to the point where it can't deliver the proper amperage, causing the fuel solenoid to drop out sometimes, especially after ~20min of use. Unbelievable, never seen anything like it.

 

[keakar]

SOLVED!!! After 3 years and over $1500 and several full days of my time thrown at this thing, I finally found the problem. And it is as stupid as you'd think. I even spent a whole day tearing off the heads and replacing head gaskets thinking that might be the issue.

At the suggestion of my father in law's mechanic friend, I ran a temp wire straight from the battery + terminal to the fuel solenoid on the carburetor. BAM, thing fired up instantly and ran perfectly.

Bottom line is, although I measured 12.5V at the solenoid connection point, something is pinched or frayed somewhere to the point where it can't deliver the proper amperage, causing the fuel solenoid to drop out sometimes, especially after ~20min of use. Unbelievable, never seen anything like it.

well you are not solved just yet, that still needs to run through the main switch so the solenoid only gets power when key is on or the solenoid drain the battery and/or burn up or both but it will also flood the engine with gas while it sits unused since that is what the solenoid it there to stop

trace the wire back to the switch and see if that fixes it, if not then its between thew switch and the engine and might just be in the plug for the engine

 

[dbrunone]

well you are not solved just yet, that still needs to run through the main switch so the solenoid only gets power when key is on or the solenoid drain the battery and/or burn up or both but it will also flood the engine with gas while it sits unused since that is what the solenoid it there to stop

trace the wire back to the switch and see if that fixes it, if not then its between thew switch and the engine and might just be in the plug for the engine

Right, obviously I disconnect the wire when not running the mower. I will troubleshoot the wire but at least I know what I'm looking for now, instead of wondering whether its a valve problem or clogged fuel port or something else.

 

[Scrubcadet10]

well you are not solved just yet, that still needs to run through the main switch so the solenoid only gets power when key is on or the solenoid drain the battery and/or burn up or both but it will also flood the engine with gas while it sits unused since that is what the solenoid it there to stop

trace the wire back to the switch and see if that fixes it, if not then its between thew switch and the engine and might just be in the plug for the engine

that solenoid is not there to stop the engine from flooding,, that is more or less the float needles job, that solenoid is supposed to prevent backfire. Or "afterfire"

 

[keakar]

that solenoid is not there to stop the engine from flooding,, that is more or less the float needles job, that solenoid is supposed to prevent backfire. Or "afterfire"

lol, WRONG !!!

it is there as a backup secondary safety to shut off fuel to starve the engine and shut it down

backfiring is only related to timing or improper valve adjustment