44S777 engine shutting down under load
- Thread starter Nlcowand
- Start date
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
bertsmobile1
Lawn Royalty
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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.
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 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)
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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.