Kohler CV740 only runs with choke fully closed, stutters when going up in RPM's

[Mothman]

Hi folks,

Got this Craftsman DGT 6000 running to a point, idle only.
Carburetor has been repaired, the accelerator pump diaphragm was shot, bowl o-ring was gone and it was gunked up. It's no longer leaking fuel and all jets/pipes etc are clean.
I can not find any diagrams or references to the way the throttle and choke are hooked up (see photo assembly.jpg) or even if that whole assembly is put together the right way.

What I really need is reference photos from someone that has one of these tractors so I can compare. Both the tractor and engine service manuals only mention the governor arm and not the rest of this assembly. The way it's all put together now is based off glimpses from youtube videos and experimentation.

I've had suggestions that say the fuel mix screw needs to be adjusted; my carburetor doesn't have one of those adjustment screws. Apart from the idle speed, nothing on this carb can be adjusted and it idles fine at 1000rpm. I can get the engine to 2000 rpm sometimes running smooth-ish (with choke wide open) but as soon as I drive with it, it starts stuttering and is about to stall unless I bring it back to 1000rpm. There is also a line that leads from one of the cylinder heads to underneath the air filter, that is leaking a LOT (I think it's fuel), don't know what it's called but a photo has been attached (leaking.jpg).

I don't know where to look next as I know next to nothing about engines/carbs and the likes. Mower repair shops can't come out til the end of July which doesn't help me now either so decided to just keep at it myself

Additional info (may be relevant or not):
- Fuel filter was replaced, old one was gunked up.
- All the original fuel hoses are in place, no leaks or deterioration that I can see
- Fuel tank cap breather works
- New spark plugs do not improve or worsen the situation

Hoping someone can help me make sense of this.
Thanks!

 

[StarTech]

While running do an exhaust temperature check. You might find that one side is not working.

 

[Mothman]

Never thought of that!
I ran the engine for a few minutes and checked the heat on each pipe. There is a difference but they both get hot.
30°C difference, not sure if that's relevant.

 

[Mothman]

Update; saw a video where the carburetor was taken apart and realized that my solenoid was stuck in the extended position. So ran to the garage, pulled it apart and sure enough it was all gunked up. Cleaned it and now it's moving freely and I can hear the click when I turn the ignition key. It being 2am I have not ran the engine yet but just wondering if this solenoid being stuck can have caused all of the above?
From what I read/hear it's just supposed to prevent backfiring when the engine is turned off so I don't expect it to cause trouble while in operation but of course I know nothing of these things.

 

[StarTech]

Then it sounds like you were running the engine with the choke fully closed instead of fully open. And yes could very well have been the problem as with the choke fully you were forcing the engine to fuel through a bypass method. That is like us trying to breathe through a soda straw can be done but is a lot hardier.

I didn't think about the fuel solenoid as that is one thing here I always clean and make sure it is working when depressed manually.

 

[Mothman]

Apologies, yes, choke valve on the carburetor fully closed. I messed that one up (thread title adjusted).

After cleaning the solenoid it ran great for a few hours, actually got the lawn mowed! Then it started stuttering again at higher RPM and black smoke started coming out of the exhaust.
I removed the spark plugs and they were covered in black soot, one dry, one wet. Put new spark plugs in and the stuttering was gone for a few minutes, then returned.
Removed the spark plugs again, left side clear, right side covered in black soot again.

The air filter isn't in great shape but even without the filter it produces the black smoke. Fuel is fresh and oil is full (oil looks gold brown color and is pretty runny).

Not sure if I should start a new thread for this or to just keep going here, pls let me know which is better

 

[Scrubcadet10]

Apologies, yes, choke valve on the carburetor fully closed. I messed that one up (thread title adjusted).

After cleaning the solenoid it ran great for a few hours, actually got the lawn mowed! Then it started stuttering again at higher RPM and black smoke started coming out of the exhaust.
I removed the spark plugs and they were covered in black soot, one dry, one wet. Put new spark plugs in and the stuttering was gone for a few minutes, then returned.
Removed the spark plugs again, left side clear, right side covered in black soot again.

The air filter isn't in great shape but even without the filter it produces the black smoke. Fuel is fresh and oil is full (oil looks gold brown color and is pretty runny).

Not sure if I should start a new thread for this or to just keep going here, pls let me know which is better

Oil doesn't smell like gasoline, does it?

 

[Mothman]

Oil doesn't smell like gasoline, does it?

Not from what I can tell but the whole garage/tractor smells like fuel so it's hard to tell.

 

[Mothman]

New info:
It sat for a few hours, I cleaned the spark plugs and decided to fire it up again, because why not.
Black smoke, running rough but this time it starts increasing RPM almost right away, even with the throttle all the way down.
I have to turn the ignition off as it gets close to 4000rpm (red) pretty quick. It just has a mind of it's own now.

Checked the throttle cable and linkage, they work as they should, everything still connected the way it was.
New symptom or related to the previous issues? As loud as this engine is this runaway behavior is pretty intimidating to a newbie like me haha

 

[bertsmobile1]

Run away is always because the governor is not governing the engine