[coach]

1993 STX 38 all of a sudden a week after my first cut this year is probably a good half quart high. I understand gas is getting into the crankcase. The engine runs fine otherwise.
My deere service manual talks about the needle valve in the carb bowl not seating or a gaslogged float. It never mentions the electric fuel solenoid other than showing it on the parts diagram.
From what I've heard the solenoid tends to be the problem.
Can the solenoid be taken off the carb while on the engine or does the entire carb need to be removed to work on it?
Is the solenoid serviceable?
Does the solenoid work by pushing up on the carb float when the engine is off? It doesn't appear to be part of the gas supply system otherwise.
The tractor has been sitting almost a week and there may be a slight increase of oil, but I don't see the drastic increase of the week before.
I'm just trying to learn a little more about it before I work on it.
Maybe I just had a bit of dirt. I ran some seafoam in the gas on my last cut.

 

[flynfrfun]

1993 STX 38 all of a sudden a week after my first cut this year is probably a good half quart high. I understand gas is getting into the crankcase. The engine runs fine otherwise.
My deere service manual talks about the needle valve in the carb bowl not seating or a gaslogged float. It never mentions the electric fuel solenoid other than showing it on the parts diagram.
From what I've heard the solenoid tends to be the problem.
Can the solenoid be taken off the carb while on the engine or does the entire carb need to be removed to work on it?
Is the solenoid serviceable?
Does the solenoid work by pushing up on the carb float when the engine is off? It doesn't appear to be part of the gas supply system otherwise.
The tractor has been sitting almost a week and there may be a slight increase of oil, but I don't see the drastic increase of the week before.
I'm just trying to learn a little more about it before I work on it.
Maybe I just had a bit of dirt. I ran some seafoam in the gas on my last cut.

Hi, what you need to do is install a fuel shutoff valve in between the fuel tank and the carbureator. Then each time you shut down the mower when you are done with it, shut off the fuel valve. It's as simple as that. What is happening is because it is a gravity fed fuel system, fuel is seeping past the inlet valve in the carb and filling the crankcase w/ fuel. You really need to drain the oil ASAP or you risk burning your engine up. The fuel in the oil will thin the oil out and it will not give the protection it is supposed to.

I got a carb rebuild kit for about $9 from my local John Deere dealership and installed it. It was super easy. From what I could tell, the fuel solenoid has a rubber plunger that should be stopping the fuel from flowing thru the carb when you shut the engine off. It does not push up on the float. It pushes against an open ended tube that allows the fuel to move to the venturi and then into the engine. The plunger just seals off this tube when you shut the mower down. Either the rubber plunger is worn/cracked or the fuel inlet needle valve is worn causing the fuel to seep thru your carb. A new rubber plunger came in my carb rebuild kit.

At any rate, the simple fix is to just shut the fuel valve off when you shut the engine down and this won't happen anymore. Your mower should have came with the valve, but if you don't have one, you can get them at Home Depot or Lowes. Hope this helps. BUT ABOVE ALL....DRAIN YOUR OIL AND REFILL WITH FRESH OIL IF YOU WANT YOUR ENGINE TO LIVE!
Flynfrfun

 

[coach]

Flynfrfun,
I do have a shut off, but I just don't usually use it. I will start using it now.
I was wondering how the solinoid worked. I just don't have the time to take it apart right now. After 15 year I guess the rubber could be worn.
I will change the oil before the next cut.
Thanks

 

[flynfrfun]

Coach,
Cool! Also, another good practice is to shut off the fuel valve a little before you are getting ready to shut down the engine. This way, the fuel in the lines and carb get used up and won't be able to drain into the oil after you shut it down. This will stop absolutely all fuel from getting into the oil. Take care.
Flynfrfun

 

[Walt 2002]

"From what I've heard the solenoid tends to be the problem."

"From what I could tell, the fuel solenoid has a rubber plunger that should be stopping the fuel from flowing thru the carb when you shut the engine off."

It is a popular misconception that the solenoid shuts off the fuel flow into/thru the carb. It actually only stops, or mostly stops, the flow thru the main metering jet helping prevent after fire, has nothing what so ever to do with your problem.

Walt Conner

 

[coach]

So Walt, what do you think the problem could be?
Is it the needle valve or seat, or the float like the service manual suggests?
What is after fire too? I never heard that expression. edit: I guess that's the same as backfire. Never mind.

 

[RED-85-Z51]

After fire, after run, dieseling, anti-backfire, etc.. all the same. As an engine runs there can be hot spots on the valves, piston, head, and any carbon anywhere in the combustion chamber. When an engine is shut off even though spark is taken away it can still draft fuel up through the carb, into the engine...and as the engine slows this fuel can ignite and cause the engine to continue to run solely on compression and engine heat.

The anti-deisel solenoid simply blocks the flow of fuel up the emulsion tube into the venturi and thus into the engine. IT will NOT prevent an engine from flooding of the needle and seat stick, or hang.

2 things usually cause this problem on this engine.

Busted diaphragm in the fuel pump seeping fuel in as it runs, and after it runs (much slower when not running)

Float needle/seat problem. Be it a worn or dirty needle, or something like that, I dont know.

Only 2 ways for fuel to get into an engine...the only 2 places it has access.

Fuel runs from the tank and makes first contact at th mechanical fuel pump. You have a diaphragm with a fuel side and an engine/dry side...if the pump is perforated, fuel can get into the engine there.

The line runs from the pump over to the carb, into the inlet and past the open float needle, and into the bowl, as demand requires. When sitting, if fuel is allowed to run up past what the float is supposed to allow, it wil run into the carbbody by eay of the emulsion tube or bowl vent...where it will pool until the level rises to the point it can run down into the intake valve port. If the valve is closed it wil pool and seep past the valve guide and run into the crankcase that way, or of the valve is open it will run into the cylinder and seep past the rings.

The latter of which can be diagnosed by hydro-locking on start up, or alot of smoke on start up, sometimes fuel being blown out the muffler on startup.

 

[flynfrfun]

Thanks for the clarification Red. However on the STX38, it is just gravity feed, so there is no fuel pump. I'm sure the problem is the inlet needle valve. The viton tip is probably worn, I doubt the seat has a problem as I would think the viton would wear and not the seat. A carb rebuild kit includes the needle valve.

My STX used to backfire when I quickly dropped the throttle. After rebuilding the carb with the carb kit, it totally went away. I found that the carb nuts were not holding the carb against the intake header of the engine very tight (the nuts were not very tight at all). So, it was either that or the rebuild that fixed the backfiring. Also, the mower does not surge at all when mowing at full throttle. Before the rebuild, it would vary RPM even when cruising on level smooth ground.
Flynfrfun

 

[coach]

I changed the oil and checked things out a bit tonight and as flynfrfun said their is no fuel pump, so I'm guessing a bit of dirt or a worn needle. Since the level didn't seem to change this week, I'm guessing dirt and maybe the seafoam did the trick.
I'll keep an eye on it and use the manual fuel shutoff. Unless something else happens, I think I'll wait until the off season the rebuild the carb.
Thanks for the help.

 

[flynfrfun]

I changed the oil and checked things out a bit tonight and as flynfrfun said their is no fuel pump, so I'm guessing a bit of dirt or a worn needle. Since the level didn't seem to change this week, I'm guessing dirt and maybe the seafoam did the trick.
I'll keep an eye on it and use the manual fuel shutoff. Unless something else happens, I think I'll wait until the off season the rebuild the carb.
Thanks for the help.

Yeah, unless it starts having backfiring problems, or running bad there is no need to rebuild the carb right away.

Personally, I'm not a believer in Seafoam. I did a little test to see for myself if Seafoam can clean carbon from a combustion chamber. I removed the spark plug and checked to see how much carbon was on the piston of my weedeater before I did the test as a reference. I followed the recommended procedure of running the engine and slowly spraying Seafoam into the intake until it died. Fired it up 5 mins later and ran it until all the smoke went away. People think all that smoke is the carbon going out of the engine. But, after removing the spark plug, the piston had the exact same amount of carbon on it.:banghead3 . I did the test several times and even let it sit overnight one of the times. There was no change. So, I'm not a follower of Seafoam...at least for carbon removal. I don't know how well it works as a fuel system cleaner, as I haven't had the opportunity to test it out.
Flynfrfun

 

[coach]

I've used seafoam for a while now, first on outboard engines then on everything else. I use it mostly for it's fuel system cleaning abilities which I've seen it do some amazing things on some crapped up carbs.
I've used it for decarboning, but not sure of the results for that.