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I have B&S 44s777-0011G1 engine on a husqvarna lawn tractor. It is not running correctly. After cutting grass for 10 minutes it starts acting up and shuts down. It is then hard to start and won’t run under load. If I wait about 15-30 minutes it starts up fine and will run rather smoothly for about 5-10 minutes under load and shutdown again. I have eleminated the fuel filter, air filter, gas tank vent and water in the fuel as a possible cause. I have drained the bowl and the gas I’m using is fresh.
I would appreciate any kind of direction you may offer as to how I should proceed with troubleshooting this issue.
Thanks!

Next time it shuts down check for spark on both cylinders. You may have what is called a hot short or open, which means when the coil gets hot it will either open up or short to ground. No spark until it cools down.

How old is this machine? I wonder if the fuel supply hose is being attacked by the gas we use these days? Swells up inside and reduces flow? Something to look at maybe. Ignition, as Rivets suggests, might be the culprit though.

Rivets said:

Next time it shuts down check for spark on both cylinders. You may have what is called a hot short or open, which means when the coil gets hot it will either open up or short to ground. No spark until it cools down.

Click to expand...

Thanks for the reply!
After it shuts down under load it will start back up somewhat rough, but once I engage the blades it can’t handle the load and shuts down. Would this be the case with a bad coil?
Thanks

Great thread

Here’s a test that give us a better idea of what may or may not be happening. Next time it happens, if you have a GOOD insulated pliers, start the engine (I know it will run rough) and pull the plug wire on one side. Does anything change? Go to the other side and do the same thing. If the engine speed changes when you pull the wire, that cylinder is firing properly. If nothing changes, something is wrong with that cylinder. You now have to check for spark on that cylinder, to see if we have a spark or fuel problem. If both cylinder show a speed drop, then we will go after a fuel problem. I’ll be in and out this weekend, but will try to check back as often as possible.

I went and tried that and when I pulled the left side plup cap nothing happened. When I did right side engine died. So I guess I have a bad left side Magneto...or am I over simplifying this.
Thanks

Swap spark plugs and see if the problem follows the plug.

Now we have narrowed it down to that cylinder. Next two things to check. If you have an in-line spark tester, see if you have spark when it is running rough. After that test pull the plug and see if it is wet. No spark and wet plug probably the coil. Dry plug, I would be looking at a fuel issue. Let me know what you find and we’ll go from there.

Rivets, thanks for reply. You have been very helpful.
Ok, this morning I was able to check it out. Cranked it up and ran till it shutdown. Put inline tester in place and checked plug and I am getting a spark.
Pulled the plug and it is dry.

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.

Whatever the cause keep us updated, it will help others in the same "boat" !

Bounced the problem around at lunch today and the possiblities we came up with are; fuel solenoid shorting due to heat but doubt due to easy restart, bad gaskets either carb or intake manifold opening when they heat up, bad pulse hose on the fuel pump open when hot and bad head gasket. The one thing that confuses us is that when you pulled the plug wires during rough running, you had no change on the left cylinder. This normally indicates a bad head gasket or bad coil. The other tests you performed to narrow the problem down didn’t indicate either one. Not being able to put a load on the engine indicates it is only running on one cylinder. Why is what we are trying to solve. I don’t like to breakdown and rebuild carbs unless I’m pretty sure that is the cause or as a last resort. Just wish I was standing next to you, would make this a lot easier. Still think I’m missing something simple. Going to ask another tech to jump in on this one and see if he has any ideas. We normally try to stay out of the way of other techs posts, just st gets confusing, but I need someone else to take a stab.

Rivets, after reading through the thread, I am wondering if the intake manifold is made of plastic or aluminum. I am wondering if it is plastic and warping either at the head or at the carb gasket interface,. Both have been an issue with the plastic intake manifolds. May not be a bad idea to pull the intake manifold and make sure the area where it connects to the carb and at the head interface is flat and not cup shaped

As there were others with a lot more experience than I working on this one I was reluctant to step in and more than curious to see what the outcome was.
SO now that we are down to really left field options, there are a few things to try.
Do them one at a time because that is the golden rule in isolating obscure problems.
1) replace the fuel shut off solenoid with a short bolt make sure it only just protrudes into the float bowl.
if that makes no difference then the solenoid is good.
2) replace the fuel solenoid and remove the kill wires from the magneto coils. Check that the solenoid will shut down the engine when the mower is turned off.
To protect yourself and others around you run some jumper wires from the coils to the operators station and clip them some where that you can ground them quickly in an emergency situation.
Make sure that the wires are not touching each other and check you can shut down by grounding them.
When you mow remember that all of the safety features are now dissabled so you can drive away with the brake on for instance.
If this makes no difference then the safety / cut out circuits are good so you are looking at either the engine or fuel delivery system.
3) jerry rig an alternative fuel tank with a tap on the fuel line above the carb so it can gravity feed.
Put a joiner in the end so when the mower starts to play up you can whip the carb fuel line off the pump and plug in the alternative tank.
Problem remains then it has to be internal to the engine carb & manifold.

From what has been said so far, I am leaning towards a loose valve guide or valve seat but it is prudent to eliminate everything else first.
I eliminate gaskets & warped sealing surfaces by making up gaskets from rubber 1/16" or 1/8" depending which sheet I can find first.
On singles it is easy cause you can flood the area around the manifold with WD 40 or similar when the engine is running bad but on V twins this is not easily done cause you just don't have clean access to it without pulling 1/2 the engine apart by which time it has cooled down again.

You now have a couple of ideas how to proceed. As you can see we are scratching our head also. Patience is now going to be your friend and work through this project slowly. Post back with results and we’ll be waiting to help.

After I concluded (with the help of this forum) that it was not an ignition system issue I decided to start with the carb and do a rebuild/cleaning. Took it down and did the rebuild and did not find anything of significance. When I was reattaching the manifolds to the carberator I discovered two cracks in the bottom side of the manifold supplying the left cylinder. These were large enough to allow considerable air to enter (see attached pic). I’m convinced this is the culprit of my issues.
I would like to say this is one of the better experiences I have had on a forum. I received relevant and helpful input and guidance on my issue. It was a good experience. Thanks to all (especially Rivets)

I'm really glad I've got the aluminum manifold on mine, saw some available on several sites mainly Evil-Bay ..........

Haven't seen any of the manifolds crack like that, but have seen the carb mounting surface on both the plastic and the aluminum get pulled from its normal flat surface.

I new there was something simple I was missing, plastic manifold. Never even crossed my mind, that’s why I was swinging in the wind with ideas at the end. Thank you IL and Bert for your help. I know you were staying out of the thread until I needed help, which made it easier for the OP to follow. Jumping in when you did was perfect timing.