Zg227 rich condition on restart when warmed up

[mvan85]

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]

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]

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]

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]

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]

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]

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.

 

[MountainMeadows]

When you had the carb apart did you blow out all the ports with compressed air? The smallest amount of jelled up ethanol can block these ports and cause a rich condition.

 

[mvan85]

When you had the carb apart did you blow out all the ports with compressed air? The smallest amount of jelled up ethanol can block these ports and cause a rich condition.

I did not, however I did remove the bowl and the needle and made sure it was moving freely and nothing was in between the needle and seat preventing a good seal. It seems that the issue is resolved based on changing the shut down procedure, where instead of idling down to below half throttle, I turn it off at 3/4 throttle. This is what the operators manual suggests, and seems to make sense since the solenoid that cuts off the fuel when the ignition is turned off is connected to the high end circuit, preventing extra fuel from being pulled into the cylinder after the ignition is off.

If I run into more issues, I will definitely do a thorough carb cleaning, since most of the time, the carb ends up being the source of the problem, at least in my experience with carbureted small engines.

 

[Captain13]

Glad you were able to get it going Right.

 

[lugbolt]

it wasn't uncommon for them to do that

The carb. Look where it's at. It sits down in between the cylinder heads.

when u shut the engine off, what happens? It gets hotter briefly before it cools. It's air cooled, and the cooling air comes in the front of the engine, under the seat, and the screen for the flywheel/fan assembly often gets plugged or restricted. I suggest keeping that area under the seat squeaky clean if possible.

Now then even with a clean screen, they'll sometimes to it. Because of where the carb is placed (in between the heads), when u shut the engine off and let it sit, the carb heat soaks from the lack of airflow and the heat of the engine getting even warmer. The bowl in the carb has some fuel in it, it boils and then the next time you start it, if it's not cooled off enough you'll get a flooded engine symptom. Not uncommon. Even more common if it's stored while hot in an enclosed area--e.g., enclosed trailer or garage.

The fix? Nothing you want to hear. Park it outside. Park it for longer than 45 minutes. Park in front of a fan on hot days. Some have added a little fan on the side that blows air over the engine, and Kubota actually sold us some kits to do this, although the jury was out whether or not they actually worked. And the kit was expensive for no more than it came with, a couple wires, connectors, thermosensor, and a little 6" 12v fan, oh and a couple brackets to mount the fan, relay, and the thermosensor.

 

[RBsingl]

Excellent analysis and advice Lugbolt! I would add that the fuel blend (and not just ethanol addition but other characteristics of the fuel to meet EPA seasonal and specific region air quality standards) will also play a role in the likelihood and extent of this problem because these effect volatility of the fuel.

Prior to the 1980s, a related issue impacted many cars and trucks. Not only could they have issues with boiling gas in the carb causing a hot restart issue, they were also subject to vapor lock from fuel vaporized in the line from tank to carb causing inability to hot restart or even stalling in stop and go traffic from heat buildup under the hood.

The move from carburetors and low pressure mechanical fuel pumps to fuel injection with higher pressure electric fuel pumps made this issue go away. Most modern vehicles use gas direct injection engines where the high pressure pump is fed with 50-60 psi fuel from a tank mounted pump and the mechanically driven high pressure pump supplies the injectors with pressures approaching 5,000 psi when the engine is producing maximum power so vapor/boiling fuel in the lines is no longer an issue.

 

[lugbolt]

Excellent analysis and advice Lugbolt! I would add that the fuel blend (and not just ethanol addition but other characteristics of the fuel to meet EPA seasonal and specific region air quality standards) will also play a role in the likelihood and extent of this problem because these effect volatility of the fuel.

absolutely and I'll expand on that.

Winter blended fuel will sometimes boil at as low as 80 degrees F at sea level air pressure. Summer fuel boils at a much higher temp.

This was a big issue when I worked on motorcycles. A certain brand and model would often dump the majority of it's contents out of the carburetor when you shut the engine off after a highway run. The air cooled engine would be hot enough, and the fuel tank sits directly over the top of the two cylinder heads, and there was sufficient heat to boil the fuel tank's contents. Then it would dump right out of the carburetor, through the filter box, and onto the side of the engine eventually reaching the ground. It wasn't near hot enough to ignite but I had heard that certain aftermarket exhaust systems would place the front cylinder's exhaust pipe such that drippage out of the carb might be a fire hazard.

That particular model was ditched in favor of the larger yet cubic inch engine that was designed from the get-go for EFI. Runs at 40 psi fuel pressure (max)--and normally with vacuum it would be in the low to mid 30's. Still a LOT higher than a carburetor system which was 2-5 psi. They needed a LOT of volume but little pressure.

They formulate the fuels such that in the winter time the engine starts better and warms up faster. Also, winter fuel will generally last longer before going sour so long as the container it's kept in is sealed. Vented containers will let it evaporate and what's left behind is just junk, sorta like saltwater. This is fine for most modern cars but those of us who have older stuff may have issues, as well as those of us who have carburetors on lawn mowers, boats, etc. Inboard/outboard powered boats were notorious for this because the engine, usually an automotive style engine with a few mods, sits in an enclosed space where it can get kinda hot, and they used carburetors on them for a very long time-lot longer than on cars/trucks. With that in mind, it's imperative to run the bilge blowers for a while before cranking the engine. Especially if it's got winter blended fuel which evaporates out of the bowls and fills the engine compartment with fumes. I have seen many a I/O powered boat explode because of exactly this and they are never a pretty sight. Around here the switch from winter to summer fuel is around mid April, give or take, and from summer to winter fuel in November.

 

[mvan85]

Lugbolt, I think you are probably spot on with your assessment regarding heat soak of the carb. This issue seems to occur most often on warm days (80-90 degrees, and on the humid side), after I've been running it for about an hour. If I turn it off, and within 5 mins or so, go to start it up, it's fine, but if I leave it for a longer period of time, it tends to miss, and stumble a bit before clearing up and running OK after that. The carb placement is not ideal, being buried down in between the cylinder heads.

The issue occurred again this past weekend, so I think I'll try to let it run for about a minute before shutting down, to allow the fan to pull some of the heat out of the engine, rather than just turning it off right when I park it. I assume as soon as I turn it off, there is probably an increase in engine compartment temps for a while after, since the fan stop as well. Maybe opening the "hood" would help get some air to circulate too.

Based on what you're saying, it's an issue that is more of a design flaw, exacerbated by fuel or environmental conditions, and not something I can troubleshoot a whole lot more than I already have. Sounds like I may just have to accept it as normal for the machine, or try to change how I go about my shut down procedure to allow for extended cooling before turning off the ignition.

I appreciate the feedback!

 

[lugbolt]

yeah the engine is not really a kubota engine...well it is, but it's original design came from Robin, part of Subaru. Subaru, robin, Fuji...kinda all under the same umbrella. You get the idea.

Yamaha bought out Subaru's small engines in I think 2016? I forget the timeframe.

--anyway--

When the engine was originally designed, fuels were different, and so were the regulations. as that all changed as it always does on a continual basis, some changes had to be made, but some weren't-and the engine was put on the Kubota equipment with some of the changes.

Sometimes I wish they'd used a different engine but that little V-Twin IS a great engine, despite it's few flaws-of which the biggest is the one we've been discussing (fuel boiling).

One oddity of that particular engine (all of the KZG770's) is that they have an automatic compression release, but it only releases compression on ONE cylinder. Sometimes when they get some hours on them, they'll kinda kick back upon a hot start. Normally a valve adjustment solves it-and the reasoning behind it is that over time and use the valves will get loose (and you don't usually hear them because of the valve cover's thick design). The compression release is a little "button" on one cam lobe that opens one valve just before TDC to let some pressure out. It only opens the valve just a few thousandths and for a very short time. When the clearance between the rocker arm and valve stem gets loose, as it usually does, the compression release becomes less effective and then you start noticing some harder starting and occasional kickback. And--these little engines will throw you for a BIG loop if you are doing a compression test, as one cylinder might be 200 psi and the other might only be 50 or 60 psi.

ZG222, ZG227, ZG327 all use the exact same long block. THere are two differences. One, the 27hp versions use an oil cooler where the 22's dont. And secondly the 27hp version doesn't have a restrictor behind the carb, the 22hp's carb spacer has tiny holes in it which restrict the amount of air that the engine can aspirate-reducing the engine output by about 5hp. So you can order the spacer (insulator I think they call it) for the ZG227 or ZG327 and install it on a ZG222 for a 5hp improvement, BUT, you'd be wise to change the oil often as it will get hotter

 

[BruceP]

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

These symptoms sure sound like vapor-lock.
Essentially: The gasoline in the carburetor bowl begins to boil from engine-heat when parked. As it boils, it gets into the intake-plenum. This makes for hard-restarting and rich-running for a minute after it does start.

Remember, as the engine runs CONTINUOUSLY, there is a constant flow of fresh, cold, gasoline into the carb. This helps to keep vapor-lock from happening.

Cars used to experience vapor-lock pretty regularly when they had carburetors on them.

On a related subject:
With ALL my small gas engines, I always turn off the gas and allow the carburetor to run dry when the machine is not in use. This practice will prevent carb. problems for many years.

This is because during storage, the gasoline constantly evaporates from the carburetor bowl. Fresh gas fills the bowl back up... this processs REPEATS until the fuel-tank is empty. All the residue from evaporated gasoline ends up in the carburetor and pluggs up the jets.

I work on many small engines every week and the #1 problem is plugged-up carburetors from storage. The ethanol in the gasoline REALLY messes things up of the gas is not turned off during storage.

 

[mvan85]

Lugbolt, I did do a valve adjustment at the end of the season this past fall. It's possible I didn't do it perfectly as it was my first time doing a valve adjustment on this engine. I followed service manual specs, and did my research, but who knows...I'm going to check the valves soon, maybe this weekend to see if they are within spec.

And yes, I was in a panic briefly after testing compression shortly after I got the mower last year. One cylinder was around 180 (I think left side) , the other around 60. Figured I got ripped off buying a mower with a bad engine...After some research I learned about the compression release, which explained the difference in compression readings.

I appreciate all of the insight you are all offering. Hard finding much info on the gas engines associated with this Kubota zero turn. A lot of diesels out there, but not much on the forums for the gasoline engines and associated issues. Hopefully this thread helps others like me who have been running into this issue.

 

[mvan85]

Lugbolt, I did do a valve adjustment at the end of the season this past fall. It's possible I didn't do it perfectly as it was my first time doing a valve adjustment on this engine. I followed service manual specs, and did my research, but who knows...I'm going to check the valves soon, maybe this weekend to see if they are within spec.

And yes, I was in a panic briefly after testing compression shortly after I got the mower last year. One cylinder was around 180 (I think left side) , the other around 60. Figured I got ripped off buying a mower with a bad engine...After some research I learned about the compression release, which explained the difference in compression readings.

I appreciate all of the insight you are all offering. Hard finding much info on the gas engines associated with this Kubota zero turn. A lot of diesels out there, but not much on the forums for the gasoline engines and associated issues. Hopefully this thread helps others like me who have been running into this issue.

Quick update...I checked the valves yesterday, and they were all within spec, and exactly where I set them last fall, so that's unlikely to be the culprit. Going to chalk this up to vapor lock from the carb being heat soaked after the engine is turned off, and the fan no longer blowing air over the engine.

 

[RBsingl]

Good p

Quick update...I checked the valves yesterday, and they were all within spec, and exactly where I set them last fall, so that's unlikely to be the culprit. Going to chalk this up to vapor lock from the carb being heat soaked after the engine is turned off, and the fan no longer blowing air over the engine.

I despise ethanol laced gas for many reasons and one of its bad features is it increases the likelihood of vapor lock, this is another reason to try to use ethanol free in power equipment. https://www.pure-gas.org/ provides a decent site for locating pure fuel in different areas. Also make sure to use up any fuel purchased during fall/winter before warm weather returns, it is blended to have a lower boiling point than spring/summer fuel so it is far more likely to lead to vapor lock issues.

I always let equipment engines cool for a few minutes after they have been working hard but in this case it would probably have little impact on heat induced vapor lock since heat is being conducted from the stopped engine to the carb assembly and it doesn't take much heat to cause vapor lock with a volatile gas blend.

Towards the end of the carb era in cars, manufacturers were experimenting with insulating gaskets and composite intake manifolds to reduce this problem and aftermarket guys often use phenolic spacers with carbs to change performance AND avoid the issues of after-run heat soak but it isn't worth experimenting in this case.