300 lawn runs 20 mins then backfires and dies

   / 300 lawn runs 20 mins then backfires and dies #31  
I'd be pulling the head(s) and looking at the valves, seats, and piston rings.
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#32  
Reading where a plugged breather could cause blowback out the dipstick. The breather tube was not pulled through into the air cleaner, but that was not the issue. However maybe the overfilled oil or some other plugged the interior breather.
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#33  
Midniteoyl said:
I'd be pulling the head(s) and looking at the valves, seats, and piston rings.
Click to expand...
That's next after digging into the breather. Engine was rebuilt 15y ago and not used heavily, so I'm wishful thinking ;-)
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#34  
Mystery continues. I let it sit for over a week. Last night I pulled off the air cleaner and tried to remove the breather cover. I got it loose (one nut in the center of the cover), but could not remove it as it sits behind the carb. I put it back, and for the heck of it, blew compressed air into the little rubber breather tube thinking maybe something was plugged. Buttoned it back up and ran it for at least 30m. No issues. I feel a slight vacuum on the dipstick while it's running.
 
   / 300 lawn runs 20 mins then backfires and dies #35  
Yes, overfilling the oil can cause these issues. Glad you have it taken care off. A full breather chamber can't function. A crankcase w/o a healthy pulse can't run a pump that is oil soaked on the vacuum side either. It doesn't seem like you took the initiative to slosh the fuel out of the tank and check for debris in the tank and pick up. Hopefully you don't get to do this allover again...
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#36  
Ye
tomplum said:
Yes, overfilling the oil can cause these issues. Glad you have it taken care off. A full breather chamber can't function. A crankcase w/o a healthy pulse can't run a pump that is oil soaked on the vacuum side either. It doesn't seem like you took the initiative to slosh the fuel out of the tank and check for debris in the tank and pick up. Hopefully you don't get to do this allover again...
Click to expand...
Yeah I really don't feel like I've gotten to the root cause. Or maybe it was that connector at the coil, or something in the fuel line. Fuel ran good out of the line at the pump. Who knows.
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#37  
Still stalls after 20-40 minutes. Maybe replace condenser?
 
   / 300 lawn runs 20 mins then backfires and dies
  • Thread Starter
#38  
Replaced fuel pump. Maybe problem solved. I used a cheap $13 one from Amazon but it looks ok. We'll see.

Another issue - the rectifier is outputting -2v DC (yes minus). AC across its two terminals is 38v AC. I replaced the original Kohler awhile back. What DC should I see? I felt like issue with original one was too high of voltage and it damaged the battery. I'm guessing around 13v to 14v would be right.
 
   / 300 lawn runs 20 mins then backfires and dies #39  
You should have battery voltage at that terminal of the regulator to start with, so I would guess that's your issue. Yes, once you are running, higher voltage in that range.
 
   / 300 lawn runs 20 mins then backfires and dies #40  
I had a JD 300 lawn tractor that would quit after about 2 hours. Mine it was the exhaust valve would stick open when hot. IIRC later models got a sodium filled exhaust valve to cure that problem.
My lawn took longer than 2 hours to mow, so I traded it in for newer model.
 
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