44S777 engine shutting down under load

OK, I think you may have a valve problem on that cylinder. Time to carefully pull the valve cover (we don’t want to ruin the gasket if possible) and both spark plugs. With the plugs out you should be able to rotate the flywheel by hand, unless your engine has a cover over the flywheel screen. Check and see if you have very little play on the rocker arms. A lot of play means the valve clearance is way off. As you are rotating watch the valves, I’m betting the intake is not opening. I’ve attached a manual which will be of some help. Let me know what you find.

https://drive.google.com/file/d/0B6NaqjIxWV1ySkZjTTA5TGltZEE/view

Ok, as you suggested I removed the valve cover and the valves, springs, rocker arm, supports, and push rods and nuts and all look good. Everything seems tight and proper. I rotated the flywheel and everything seemed smooth. I measured the stroke on both valves and it was the same for both at approximately 1/4 inch.
To my untrained eye everything seems normal.

I wish I was there, as now I’m confused, so I’m going to ask you to do something again I’ve asked before. Not to be a jerk, just to refresh my brain. Put the inline tester in the left side cylinder wire and watch the spark. You say it runs fine for about 10 minutes, it should have a strong steady spark during this time. When it starts running rough, does the spark change, hate to say but watch carefully, as it may be very little. If the spark stays strong, see if choking the engine a little has any reaction. Does this only happen when the unit is under load? Is anything else happening that you may have forgotten to tell me. I’ve reread your posts and have a feeling I’m missing something simple? Sorry about the questions.

I’ll go back and do as you suggest. However, I am temporarily shutdown due to rain. Something that may be helpful is the spark plug that I pulled on the left side. One of the first things I did was change the plugs to new ones. The left plug was dry when I did that and the color of electrode looked a little unusual. I’ll attach pics... you may see something. The closest plug is the one in question (left side).
Also of note is this engine is 4 years old and has 172 hours on it... not very old.

If those two plugs were installed at the same time, I don’t think we have an ignition problem, but I have been prooven wrong before. They look good. I’m hopeful that choking the engine will make it running better for a minute or two. This will indicate a fuel problem. Sorry I’m going in circles, just that I’m not standing beside you to try combinations of different tests. One other test you can do before posting back is; while the engine is running rough, carefully loose the oil fill cap and tell me what you see. A lot of smoke, feel pressure coming out, spraying oil, etc. do this with a rag to protect your arm and hand.

Ok, I’ve had a chance to recheck the left cylinder under both conditions (startup and after shutdown) and I cannot distinguish any difference in the spark on the tester. It fires fast under both condition so I may be missing it, if there is a difference.
The problem I am having is under load. After it shuts down under load it will crank back up without load. It is a little rough and sluggish for about 30 seconds and then settles down and runs smoother. However, if I attempt to engage the blades it shuts down again and it will start back up after that following the same pattern just described. If I shut it off and let it sit for about 30 minutes it will then run under load for about 10 minutes.
As you said in your last post, I also don’t think it is an ignition issue and is somehow fuel related. I also think the fuel issue may be constant and there all the time but shows itself under heavy load and higher ambient temp.
Of all the times I pulled the left plug, even when i originally changed it, it was dry every time.
Another point that I realized just now is the ambient temp seems to make a difference. I got up this morning and decided to check it out and do some test on it but I couldn’t get it to shut down on its own. It was probably about 82 outside. A couple hours later it shutdown after 10 minutes. During the middle of day we have been running in mid upper 90,s. This repeated a few minutes ago and it is now mid 80s and I could not get it to shut down

Have you tested the out put on the fuel pump, both when running smooth and rough. Take a piece of hose and hook it to the output side of the pump have the other end in a container. Remove both plugs and crank the engine over for ten seconds and measure the output. Replace the plugs and run the unit until problem shows up, then repeat the test. If you don’t have the same output, you may have a pump problem, depending on the difference. On another note, I’m still confused with the results of the left cylinder test, why we would have no fuel to be side. Going to bounce it off a couple of techs at work today. I’ll try to get back to you this evening.

If I may offer, is it possible the problem may be the carburetor ?? I believe this engine has the Nikki 2 Bbl. carb. on it (according to parts manual) I've heard that sometimes the main jets in the transfer tube become loose and create problems, check out this link and if you decide to check into the carb as a last resort, this may be helpful,

https://www.youtube.com/watch?v=I_k1ystbSWs

I had a very similar problem with my mower last year and went thru same tests and finally fixed the problem. the following is what I did.
1. Removed carberator, dissasemble, clean, replace all gaskets and jets.
2. Check intake on heads for any obstructions. Bad gas will leave a honeycomb residue that will build up and rob power.
3. Replace intake gaskets.
4. Check for proper operation of fuel shutoff. If in question replace.

Boobala said:

If I may offer, is it possible the problem may be the carburetor ?? I believe this engine has the Nikki 2 Bbl. carb. on it (according to parts manual) I've heard that sometimes the main jets in the transfer tube become loose and create problems, check out this link and if you decide to check into the carb as a last resort, this may be helpful,

https://www.youtube.com/watch?v=I_k1ystbSWs

Click to expand...

Thanks for the input. I’m getting close to feeling the my carb might be main issue.