Z121S Mows Fine for 30 minutes then Loses Power

[stevobags]

Hey All,
Im running a Z121S with about 145 hours and four years old. All pms and services up to date.

I can mow with no problems for about 30 minutes and then the unit starts to get sluggish and slows down. I disengage the pto and the unit returns to normal.

Today, filled fuel tank half way with fresh non ethanol fuel. I blasted the carb with cleaner before I hit the grass. Fuel filter is new. It still only runs for 30 minutes. I let it cool down and then i do the dance again with it. I have to vote for a fuel issue, carb? What bugs me is why will it run for 30 minutes and then go sluggish? Is there something in the carb that will fail after it heats up?

Any thoughts would be appreciated. Plus, my carb experience is very limited, best way to troubleshoot?

Be Safe! Steve

 

[flogler]

Engine is overheating but on that fine line. Is fan running or any debris on flywheel or broken fins? Thats my theory anyway-or fuel filter is dirty and can't suck enough for loaded power.

 

[Roadworthy]

Check for debris preventing your fuel tank cap from venting.

 

[stevobags]

Check for debris preventing your fuel tank cap from venting.

Agreed, how do you tell if there is debris? I see no holes and it is the stock cap.

 

[Roadworthy]

Try putting your cap on loosely, don't tighten it down. See if that helps. Vented caps don't necessarily have obvious holes but there can still be an air path through the cap.

 

[lugbolt]

raise the seat. Find the fuel shutoff valve. Remove the valve from the tank, just yank up on it. Disconnect the fuel line first. Then pull the tube off of the valve and blow the valve out from the fuel line side and see what kind of junk comes out. If you find anything in it, be sure to look down inside the tank to find the source of it. I see grass in there ALL the time. I can tell you this: getting the tank out of one of those mowers is a chore so consider yourself blessed if you don't find anything inside the tank.

#1 cause of sluggish operation is the fuel pickup tube. Kubota has addressed it, the new ones have a little screen on the end and if yours doesn't have that, you'd be wise to replace it with the new style (old style NLA, superceded to the new style).

#2 cause is failing ignition coil, common Kohler item. Usually exhibits itself via low power, but also like the engine is running weakly on one of the two cylinders. To me (trained ear) it's obvious when it happens but not everyone knows what to look for.

Someone mentioned overheating. Yeah that happens too, when the screen on the top of the engine gets plugged up with clippings. Usually the tip of the dipstick tube turns from yellow to brown/black when it's been severely overheated. If you see a dark brown stain on the end of the dip stick, your engine has been overheated.

 

[stevobags]

Try putting your cap on loosely, don't tighten it down. See if that helps. Vented caps don't necessarily have obvious holes but there can still be an air path through the cap.

I shall give it a shot, thanks!

 

[stevobags]

raise the seat. Find the fuel shutoff valve. Remove the valve from the tank, just yank up on it. Disconnect the fuel line first. Then pull the tube off of the valve and blow the valve out from the fuel line side and see what kind of junk comes out. If you find anything in it, be sure to look down inside the tank to find the source of it. I see grass in there ALL the time. I can tell you this: getting the tank out of one of those mowers is a chore so consider yourself blessed if you don't find anything inside the tank.

#1 cause of sluggish operation is the fuel pickup tube. Kubota has addressed it, the new ones have a little screen on the end and if yours doesn't have that, you'd be wise to replace it with the new style (old style NLA, superceded to the new style).

#2 cause is failing ignition coil, common Kohler item. Usually exhibits itself via low power, but also like the engine is running weakly on one of the two cylinders. To me (trained ear) it's obvious when it happens but not everyone knows what to look for.

Someone mentioned overheating. Yeah that happens too, when the screen on the top of the engine gets plugged up with clippings. Usually the tip of the dipstick tube turns from yellow to brown/black when it's been severely overheated. If you see a dark brown stain on the end of the dip stick, your engine has been overheated.

Thank you so much for the input. I did look in the tank yesterday before posting, looks clean. I also cut the end of the tube so it has the "v" shape. One or two coils on these units?

 

[lugbolt]

Thank you so much for the input. I did look in the tank yesterday before posting, looks clean. I also cut the end of the tube so it has the "v" shape. One or two coils on these units?

two, one for each cylinder.

If your tube didn't have a screen on it, go get a new valve assembly. No amount of cutting, Vee cutting, or any other cutting will solve a recurring issue. REPLACE IT (asap). K3011-92420. It's like $20 or so, comes with new grommet too. If I was close and I had one, I'd give it to you. They are "that" problematic. Junk gets stuck in the valve not the tube, so they put a screen on the end of the tube to keep the junk from getting into the valve. And it works great. Serial number 28016 (going off of memory here) and up already have the new style valve/tube assembly with the screen, prior numbers do not but the new ones retrofit with zero issue.

 

[whitetiger]

Thank you so much for the input. I did look in the tank yesterday before posting, looks clean. I also cut the end of the tube so it has the "v" shape. One or two coils on these units?

Did you blow backward through the shutoff valve?

 

[stevobags]

two, one for each cylinder.

If your tube didn't have a screen on it, go get a new valve assembly. No amount of cutting, Vee cutting, or any other cutting will solve a recurring issue. REPLACE IT (asap). K3011-92420. It's like $20 or so, comes with new grommet too. If I was close and I had one, I'd give it to you. They are "that" problematic. Junk gets stuck in the valve not the tube, so they put a screen on the end of the tube to keep the junk from getting into the valve. And it works great. Serial number 28016 (going off of memory here) and up already have the new style valve/tube assembly with the screen, prior numbers do not but the new ones retrofit with zero issue.

Thank you! My serial number is 13108. Oldie but still a goodie. Ordering one tomorrow. Thank you!!

 

[stevobags]

Did you blow backward through the shutoff valve?

Not yet. On my to do list. Way to hot here in NY to even think about going to the shed! Thanks!

 

[stevobags]

Did you blow backward through the shutoff valve?

I did blow out the entire assembly. Nothing, clean as a whistle.

 

[cfrey]

raise the seat. Find the fuel shutoff valve. Remove the valve from the tank, just yank up on it. Disconnect the fuel line first. Then pull the tube off of the valve and blow the valve out from the fuel line side and see what kind of junk comes out. If you find anything in it, be sure to look down inside the tank to find the source of it. I see grass in there ALL the time. I can tell you this: getting the tank out of one of those mowers is a chore so consider yourself blessed if you don't find anything inside the tank.

#1 cause of sluggish operation is the fuel pickup tube. Kubota has addressed it, the new ones have a little screen on the end and if yours doesn't have that, you'd be wise to replace it with the new style (old style NLA, superceded to the new style).

#2 cause is failing ignition coil, common Kohler item. Usually exhibits itself via low power, but also like the engine is running weakly on one of the two cylinders. To me (trained ear) it's obvious when it happens but not everyone knows what to look for.

Someone mentioned overheating. Yeah that happens too, when the screen on the top of the engine gets plugged up with clippings. Usually the tip of the dipstick tube turns from yellow to brown/black when it's been severely overheated. If you see a dark brown stain on the end of the dip stick, your engine has been overheated.

Huge help!!!!! Thank you very much!