520xi will not start after hot shutdown (after mowing)

[doc724 925]

Hello folks

 

I have a 2002 520xi (Kohler Command V twin 20HP )machine that is great in all respects except that if I shut it down after mowing for 45-60 minutes it absolutely refuses to start.  The starter turns, it will cough but it will not respond to the throttle at all.  To me, it apprears to have vapor lock.  If you leave it sit over night, it starts right up the next day.  During mowing, the engine temperature gauge is just slightly past vertical (hot is far right) but still well in the green zone.  This problem does not happen during the winter.  My solution to date has been to never shut it down until it is driven back into the shed. 

 

So, have any of you had a similar experieince with this tractor and if so, what was your solution?  The Toro manual does not seem to address this problem

 

thx

[dsholler 54]

Not sure if this helps, but when I was in high school my friend had a 1958 Volvo station wagon that would get vapor locked. (the car was 25 years old or so when given to a teenager). After a few annoying incidents, every time we took it to the beach we carried a bucket of water with us... when the thing locked up, we poured the water on the fuel filter (an in-line one just like on the tractor) and it started right up. Maybe give it a try? If it works, it will confirm your vapor lock theory, and if it doesn't, the worst thing that happened is that you have wet shoes.

[rmaynard 16,363]

Be careful not to pour cold water directly on a hot engine. You may end up with a much more serious problem than vapor lock.

[dsholler 54]

I was being partly facetious . Personally, I would first check to see if you have fuel flowing at the carb. Vapor lock is not a bad theory, but it could also be the fuel pump being flakey in the heat, or air getting into the fuel line when it is hot. Might as well determine whether fuel flow is the problem in the first place. I have had to replace several ignition system components on cars due to heat related failures.. not sure about how the command engine works, but it may not be fuel at all.

[Rick_in_CT 156]

When the tractor is in the "no start" mode, I would check to see if you have a good strong spark from the plug wires to ground.  Make sure the fuel shut off is fully open (I would close it then open it).  If you have spark, then I would loosen the fuel tank cap and try starting again.  I know that there is a vent tube on the gas tank, maybe it is plugged and as noted above you have a vapor lock.  I just took a good look at my 5xi gas tank cap and I don't see a vent hole in the cap, so the vent hose maybe the only vent (the parts manual shows this as a fairly long hose).  I can see the end of the vent hose on mine looking at the back of the tractor up under the the center of the back fender.  Possibly a bad ignition module that when heat soaked does not work, but when cool works ok.  Carburetor fuel shut-off solenoid that will not open when hot.  I'm thinking that it is not the fuel pump if the tractor starts right up when cold and you can continue running for a long period with no problem, only after hot shut down something is affected.  Fuel flow can easily be checked, but use extreme caution if you are testing on a hot engine.  On the firewall there are three relays, when in the "no start" mode, using the butt end of a screwdriver, tap on top of each relay one at a time and see if it starts.  K1=kill relay, K2=start relay, K3=interlock relay.  Sometimes hot relays stick.  Just a few things to look at, let us know how you make out or if you need more details.  I have the Kohler service manual for these engines.

 

Rick

[doc724 925]

Rick, I will give a look at the things you suggested.  I am still thinking it is fuel related as the other electrical things you suggested seem to not allow any ignition at all.  When this is hot, it will start, run 3-5 seconds and not respond to the throttle.  Since carbs have to atomize liquid gas, if there is only gasoline vapor present, that will quickly get drawn into the cylinders and ignited an then there is no more to follow.  The gas cap should be fine as I replaced the original (the rubber seal on the underside kept falling off when refeuling) with a OEM replacement.  As you are probably aware, the diaphragm fuel pump sits on the engine tins right next to/on top of one of the cylinder heads.  As soon as the engine shuts off, the temp in that area must increase 50 degrees or so (automotive engineers call it "hot soak") and any fuel in the fuel pump must evaporate.  IF I think about how a diaphragm pump must work, it need a vacuum source (created by engine cranking), liquid fuel in, and a vent on the punp itself (there appears to be a small powdered metal filter on the diaphragm pump that must be there to let air into the backside of the diaphragm.  The mystery continues

 

Don

[doc724 925]

Hello again Rick

 

I just checked the Parts tree illustrated diagram on the carb.  There is a small solenoid attached to the carb that seems to effect the needle jets.  Any  idea how that works or impact if is gets sticky (like when it is too hot)?  I would have thought that only the throttle plate would determine gas flow, but maybe post 1996 with new EPA regs, there are now other electronic controls that play a part

 

don

[MarkPalmer 81]

That is the fuel shotoff solenoid, and it can cause the problem you are having with warm restarts if it sticks.  It's purpose is to stop the fuel flow to the main jet when the engine is shut down to prevent backfiring.  As you can guess, if it doesn't fully re-open when the ignition is activated, the engine isn't going to start. 

 

-Mark-

[doc724 925]

If you are correct, this would seem like a good candidate to check out.  Don

[bitten 134]

I had the same problem with a K series and it turned out to be the coil. No experience with a command but thought I would throw that out there.

Good Luck,

P.J.