Craftsman mower robot - Governor/choke issue - Stalls under load and won't restart when hot

[BGood]

I recently completed a robotic lawnmower project using an old Craftsman push behind mulching mower (917.388621) with a 6.75hp engine (143.016702). Actually, the mower is not entirely robotic at this point, but computer control is in the plan for the next stage in its evolution. Right now, it is self propelled using wheelchair motors, standard 2.6ghz r/c remote radio control drone technology, and a real-time 5.8ghz FPV video feed.

The electronic technology seems to be working pretty well, but the reason for this posting here is because I suspect a basic problem with the gas mower engine. The mower's mission is wildfire mitigation of my steep backyard terrain which grows waist-high native grasses, thistle, cactus, and an occasional rattlesnake. The remote control and video feed is helpful in avoiding the latter.

The specific engine problem I'm having is that when the mower encounters particularly dense or stringy vegitation and I don't back it off quickly enough, it will stall and I can't get it started again with the pull rope. Then I have to wait up to 1/2 hour for it to cool off enough to restart. It always seems to start very easily when cool.

From internet research and my engine-savvy neighbor, we suspect the problem may be with the carburator and possibly the automatic choke / governor linkage. I ordered a replacement carb which has not arrived yet, but also have have not found any adjustment instructions for the governor linkage towards the rear of the engine. I notice that when the adjustment screw is loosened, and the governor arm is adjusted rearward, the throttle valve closes. The loading of the linkage spring (when the engine is cold) pulls the governor arm frontward which opens the butterfly throttle valve.



My neighbor suggested that the governor or choke system may be reducing fuel/air when engine rpm drops in advance of a stall, and this may be why the engine is stalling. I am more concerned about having to shlep the robot back up the hill to the workshop, or wait out with the cactus and snakes for it to cool off enough to restart.

Can anyone suggest an adjustment procedure for the governor/choke linkage that will: 1) provide additional fuel/air to prevent stalling; and 2) make the mower easier to start when hot?

Thanks so much for your suggestions.

 

[Rivets]

Notice that small plastic cap next to the primer bulb, about 7 o’clock? Under it you will find the idle jet. Remove and make sure it is clean. Here is a service manual for you engine. https://www.mymowerparts.com/pdf/Te...P-4-CYCLE-L-HEAD-FLAT-HEAD-ENGINES-692509.pdf

 

[BGood]

Thanks for sending the service manual link, Rivets. I haven't fully researched my issue yet, but there is lots of info about carb and governor adjustment that gives me a much better picture of how things work. I'll take a look at the idle jet after a morning coffee primer.

 

[sgkent]

when a push mower is put into too dense a grass it will stall. That is normal. The hard restarting can be because it is flooded at that point. I learned this as a kid trying to mow grass that was too tall. I am 71 now. You need a different kind of mower or more powerful mower than a small push style mower. Or you need to mow more frequently. We used to go out with hoes once a year and knock it down. A flail mower or HD wacker might be able to pull it off.

 

[BGood]

when a push mower is put into too dense a grass it will stall. That is normal. The hard restarting can be because it is flooded at that point. I learned this as a kid trying to mow grass that was too tall. I am 71 now. You need a different kind of mower or more powerful mower than a small push style mower. Or you need to mow more frequently. We used to go out with hoes once a year and knock it down. A flail mower or HD wacker might be able to pull it off.

Good comment, sgkent. I also should sharpen the blade on the r/c mower. My larger 12 hp riding mower with 38" deck does not have similar stalling problems in tall grass, but it is too dangerous to use on the double fall line steeps.

 

[sgkent]

Good comment, sgkent. I also should sharpen the blade on the r/c mower. My larger 12 hp riding mower with 38" deck does not have similar stalling problems in tall grass, but it is too dangerous to use on the double fall line steeps.

it is 12 HP. The smaller engine mowers don't have the power. Sharpening the blade will help but not all that much. The issue is in part the mower cannot discharge the mass it is cutting, Set the blade as high as it will go and make multiple passes, or hire some goats, which is how they handle it here.

 

[BGood]

Notice that small plastic cap next to the primer bulb, about 7 o’clock? Under it you will find the idle jet. Remove and make sure it is clean. Here is a service manual for you engine. https://www.mymowerparts.com/pdf/Te...P-4-CYCLE-L-HEAD-FLAT-HEAD-ENGINES-692509.pdf

I removed the plastic cap and idle jet. It looks pretty clean to me, but when I insert a very thin copper wire into the hole in the end, it will not fully insert. Should I be able to see the inserted wire through the side holes?

 

[Rivets]

Yes, sounds like you found your problem. I suggest you SLOWLY work a piece of stiff wire into the hole until you get it fully open. It may take a while, soaking it in carb cleaner helps. So does patience.

 

[sgkent]

no. If you look at that jet it has side holes. The end is likely plugged to the outside, because the air passage is other than to the outside thru the exterior end of the jet. I would be cautious about making changes until the air jet system is inspected better. The plug in it may be intentional. I have a couple carbs that are like that. Also the end is very shiny. Tighten it but do not overtighten it or it may crush the idle passage internally.

 

[skiman]

I recently completed a robotic lawnmower project using an old Craftsman push behind mulching mower (917.388621) with a 6.75hp engine (143.016702). Actually, the mower is not entirely robotic at this point, but computer control is in the plan for the next stage in its evolution. Right now, it is self propelled using wheelchair motors, standard 2.6ghz r/c remote radio control drone technology, and a real-time 5.8ghz FPV video feed.

The electronic technology seems to be working pretty well, but the reason for this posting here is because I suspect a basic problem with the gas mower engine. The mower's mission is wildfire mitigation of my steep backyard terrain which grows waist-high native grasses, thistle, cactus, and an occasional rattlesnake. The remote control and video feed is helpful in avoiding the latter.

The specific engine problem I'm having is that when the mower encounters particularly dense or stringy vegitation and I don't back it off quickly enough, it will stall and I can't get it started again with the pull rope. Then I have to wait up to 1/2 hour for it to cool off enough to restart. It always seems to start very easily when cool.

From internet research and my engine-savvy neighbor, we suspect the problem may be with the carburator and possibly the automatic choke / governor linkage. I ordered a replacement carb which has not arrived yet, but also have have not found any adjustment instructions for the governor linkage towards the rear of the engine. I notice that when the adjustment screw is loosened, and the governor arm is adjusted rearward, the throttle valve closes. The loading of the linkage spring (when the engine is cold) pulls the governor arm frontward which opens the butterfly throttle valve.

View attachment 61396

My neighbor suggested that the governor or choke system may be reducing fuel/air when engine rpm drops in advance of a stall, and this may be why the engine is stalling. I am more concerned about having to shlep the robot back up the hill to the workshop, or wait out with the cactus and snakes for it to cool off enough to restart.

Can anyone suggest an adjustment procedure for the governor/choke linkage that will: 1) provide additional fuel/air to prevent stalling; and 2) make the mower easier to start when hot?

Thanks so much for your suggestions.

well for one, you dont have any kind of choke setup...you have a primer bulb setup designed to place gas into the carb intake tube to allow the engine to start from the extra gas in the tube...you dont have autochoke or a choke flap at all...second...when does it stall out and how steep is your hill...are you going up the hill and this happens or down...if down hill...depending on the slope of the hill...youll experience fuel starvation because the gravity feed fuel from the tank is lower than the carb...you might want to consider remotely mounting the tank higher than the engine to insure the fuel always flows to the carb going up or down a hill...also check the fuel cap vent hole to make sure its got good air venting to take up for fuel loss when running...i suspect your biggest problem is the slope youre trying to cut...