Zg227 rich condition on restart when warmed up

mvan85

New member

Equipment
Kubota Zg227 (27hp Kubota gas engine)
Jun 23, 2022
4
0
1
26035
Hi all, first time posting on this forum. Hoping to get some insight into whether this is a common issue, or something I should start troubleshooting.

I have a 2009 Zg227 zero turn with a 27hp Kubota gasoline engine. It has about 480hrs on it, and was used for residential mowing its entire life. I purchased it last year, in the fall, and didn't notice this issue until this year (maybe weather/temp related?).

From a cold start, I follow the start up process, of pulling choke, put throttle at half way position, and fire it up, then push the choke back in. Never have any issues when starting it cold. I can run it for an hour or so without any issues, even if I power down briefly while mowing my 1.5 acres.

The issue I am experiencing begins if I shut it off for 10-15 minutes or so while cleaning it off, then go to start it up to put it away. It occasionally puffs black smoke, stumbles like it's misfiring, and can even stall if I quickly push it to full throttle. If I leave it at half throttle, it quickly gets back to normal, but it seems like for some reason, when it's powered off, while hot, extra fuel is entering the combustion chamber, causing it to be too rich on a hot restart.

Note: new plugs, air filter, fuel filters, oil change within last 20 hours of use.

Any thoughts, suggestions, insight would be greatly appreciated!
 

Captain13

Active member

Equipment
M7040 4WD ROPS, ZD28, Woods (84” box blade, 72” harrow, 48” pallet forks)
Feb 27, 2019
351
110
43
Kathleen, GA
Could the carb float needle/seat possibly have some dirt in it causing it to flood on startup when hot? Sounds like it’s flooding when you shut it down. Like gas is continuing to seep past the needle valve when you shut down and the bowl is most likely full. Or maybe the float is sticking. Have you checked the choke plate when the engine is hot to ensure it’s fully open. May need adjustment there.
 

mvan85

New member

Equipment
Kubota Zg227 (27hp Kubota gas engine)
Jun 23, 2022
4
0
1
26035
Could the carb float needle/seat possibly have some dirt in it causing it to flood on startup when hot? Sounds like it’s flooding when you shut it down. Like gas is continuing to seep past the needle valve when you shut down and the bowl is most likely full. Or maybe the float is sticking. Have you checked the choke plate when the engine is hot to ensure it’s fully open. May need adjustment there.
I haven't checked the choke plate, but I will. I like the idea of the needle/seat not fully sealing when the float is pushing up on it when the bowl is full. Any idea how difficult it is to get access to the bowl/float on this particular engine? Also, is this something that can cause damage, or just an annoyance more than anything? Wondering if fuel could possibly get into the crankcase past the piston rings if too much is draining into the combustion chamber.
 

Captain13

Active member

Equipment
M7040 4WD ROPS, ZD28, Woods (84” box blade, 72” harrow, 48” pallet forks)
Feb 27, 2019
351
110
43
Kathleen, GA
If raw fuel is running in the cylinder then you could get cylinder wash down. I don’t know how hard it is to access the bowl On that engine. I had this happen on my 19 horse Honda powered splitter. It was easy to get the bowl off. There was crud in the bowl and I ended up pulling the carb to clean it.
 

mvan85

New member

Equipment
Kubota Zg227 (27hp Kubota gas engine)
Jun 23, 2022
4
0
1
26035
If raw fuel is running in the cylinder then you could get cylinder wash down. I don’t know how hard it is to access the bowl On that engine. I had this happen on my 19 horse Honda powered splitter. It was easy to get the bowl off. There was crud in the bowl and I ended up pulling the carb to clean it.
Thanks for the insight. I'll pull the intake off the carb to check the choke plate first, and if that looks OK, I'll pull the carb to inspect. The machine is 13 years old, so debris in the carb wouldn't be a big surprise. I'll report back when I get around to taking it apart.
 

mvan85

New member

Equipment
Kubota Zg227 (27hp Kubota gas engine)
Jun 23, 2022
4
0
1
26035
Update: I went ahead and pulled the air filter assembly, and verified the choke plate was opening fully when the choke is off. Then removed the carb, took the bowl off, and looked it over. It is the cleanest carb I've ever cracked open. No visible debris, gunk, or anything. The mower has a dual fuel filter (one before the fuel pump and one after), so that must really keep the fuel clean going into the carb. Float moved freely, the needle/seat appeared to move freely and seal up well also.

Without seeing any red flags, I put it all back together, and fired it up. It ran normally, no issues, however I didn't run it long, or cut grass with it.

Wondering if maybe the fuel shutoff solenoid on the high end circuit jet means I should cut the engine off at higher throttle than where I normally do. I typically power down to quarter or half throttle, then turn it off a few seconds later. Should I turn it off at 3/4-full throttle instead, to prevent fuel from coming into the main jet via the solenoid blocking the fuel at higher rpm when the ignition is turned off? That's my understanding of the solenoid, however im probably making some assumptions.

Thanks
 

Captain13

Active member

Equipment
M7040 4WD ROPS, ZD28, Woods (84” box blade, 72” harrow, 48” pallet forks)
Feb 27, 2019
351
110
43
Kathleen, GA
I did look more into your problem and it seems that you might be on to something with how it is shut down. From what I read, it allows the engine to burn off excess fuel before it stops. Now that was on a Kawasaki engine but still may be applicable to your situation. Glad everything was clean. Maybe you tightened up something that was loose in the carb. if it works fine from now on, you may never know.