John Deere STX38 Problems, Please Help!

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  #1  
Old 11-19-14, 07:11 PM
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John Deere STX38 Problems, Please Help!

Hello all, I'm new here!

This will be lengthy, I want to give you guys as much detail as I can.

I bought a JD STX38 (1994/5 is my guess from the serial number) with a Kohler CV12.5S (spec no. 1270), black deck, and hydro tranny last year on craigslist, and she ran like a stinking champion last year. I mean, just crushed whatever I threw at her.

This is also my first time owning small engine power equipment, so I did some very scant reading on winterizing last year, and apparently screwed it up, because she hasn't run right all year.

The problem is this, after some time, the motor just bogs down and dies. Sometimes I can run it for 5-10 mins with the blades going, sometimes it dies right after it fires up. Sometimes it seems like its running great, sounds good, no hiccups or jitters, then all of a sudden quits. I've done quite a bit of forum searching, YouTube watching, and service manual reading, and can't figure this out.

So here's what I've done so far.

The air filter, fuel filter, oil filter, spark plug, breather hose, fuel line (from tank to carb), and head gasket have all been replaced.

The carburetor has been taken apart and cleaned, soaked in carb cleaner for two hours, reassembled and bolted back up. While it was off/apart, the gasket, air cleaner gasket, bowl gasket, and bowl screw gasket were all replaced. I took the carb to a local power equipment store and just to see what they thought, and he said it looked nice and clean.

While she's off, the battery is at 12.7vdc. While running, its at 14.3vdc, and the rectifier/regulator has 40.5vac going through it.

I've also gone into the gas tank and fished out all of the things that had fallen in and may have been getting sucked down and blocking the flow of fuel. I also shortened then length of the fuel line to have a more direct, downward sloping angle to the line as it was too long before and had some weird bends where the fuel had to go up to get into the carb. So now its a straight shot with a gentle down angle from tank to carb.

I've also adjusted the idle fuel screw on the carb to where I feel it runs best, when it actually runs. With where it is right now, when running strong, the motor speed stays nice and even when I engage the blades and it feels real good.

But like I said, after a few minutes, it craps itself.

I've uploaded a video to YouTube, if you want to see what happens for yourself.

I'm all ears with any further troubleshooting or ideas. I think I've ruled out electrical with the numbers I told you about, and I'm pretty sure vapor lock isn't it since it does the same thing if I run it with the cap off altogether. But it still seems like a fuel issue to me.

Thanks in advance!!
 
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  #2  
Old 11-19-14, 08:02 PM
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Some models have a mechanical fuel pump. Some have a fuel shutoff solenoid under the carb. Either one could be a problem. Also, check for loose wires - both low voltage (12V) and the spark plug wire.
 
  #3  
Old 11-19-14, 08:56 PM
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I'll check for the pump, and the wires tomorrow. Mine definitely does not have the fuel shutoff solenoid on the carb though.

I'll update soonest.
 
  #4  
Old 11-20-14, 03:53 AM
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cburns,

I happen to have a user manual for that model machine. If you want it PM me and I can e-mail a PDF formatted copy to you.
 
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Old 11-20-14, 06:03 AM
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@Norm, are you referring to the motors service manual, or a JD one? I have the Kohler manual, but I'd definitely appreciate the JD one if that's what you've got!

My model is also not equipped with a fuel pump.
 
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Old 11-20-14, 10:55 AM
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Grab an inline spark tester from an auto parts store and put it in and watch to see if it quite firing when it dies. This way we can pin it down to one side or the other (fuel or ignition).
 
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Old 11-20-14, 02:17 PM
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cburns,

This is the owners manual that came with the unit. I don't remember what kind of engine or if it had a pump or not.
Cover photo.



If you're still interested let me know.
 
  #8  
Old 11-21-14, 06:57 AM
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Norm, my serial falls outside of that range... Thanks though!!!

So, thanks for the responses all. Turns out the main jet in the carb was still gummed up. I took it all apart and ran cleaner through it, then boiled it for a half hour, then soaked it in cleaner, then ran a can of cleaner through it again, and it worked!

Thank goodness!

But now the stupid thing won't start! It sounds like the starter motor is turning, but the flywheel isn't moving.... So now I'm trying to figure that out. Going to test the solenoid today, but that should be fine if the starter motor is turning, right?
 
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Old 11-21-14, 09:56 AM
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If the starter is turning, the solenoid is okay. The starter drive gear is bonded to a rubber clutch on the underside. This rubber gets dry and dusty, or wet/oily, and it causes it to slip. Take it off and clean it well to restore function in most cases.
 
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Old 11-21-14, 11:04 AM
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Thanks cheese. I posted this in the am to gather some advice for when I get home! I'll get the starter off when I get home and see what happens.

Saw a youtube vid that sounded exactly like my issue, and the drive pinion was destroyed, so it couldn't engage the flywheel. That's what I'm hoping my issue is. I'll know soon!
 
  #11  
Old 11-21-14, 03:50 PM
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That happens on the briggs engines, not the kohler. (pinion destroyed)
 
  #12  
Old 11-23-14, 09:00 AM
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Mission accomplished!

I took the starter apart, cleaned and greased it, and bolted it back up, and she turned right over. Thanks for all the help guys.
 
  #13  
Old 11-23-14, 09:51 AM
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Glad you got it all fixed. Remember if you want that manual it's waiting for you.
 
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