I have a 2008 RTV500 UTY. I bought it used a couple of years ago. Was like brand new. Currently has under 200 hrs on it. I use it mostly to plow snow. Which it does awesome at. Otherwise it is stored inside and gets used occasionally for other tasks.
The RTV500 is a gas unit.
It starts and runs like a top. Except in one situation. When it sits in the sun and the ambient temp rises to 80 degrees or higher it will not start. It will crank and try to start one time and that is it. It will continue to crank but will not fire again. Once the temp drops, especially if the location becomes shaded. It will fire and run like a top.
I have taken it to my Kubota dealer. They could not figure it out. The service manager talked with someone who told him it could be the throttle position sensor. About a $200 part and the engine would need to be removed to replace it to the tune of $1200 not including parts and there is no guarantee that is the problem.
I emailed Kubota and while they did contact me it was to tell me to work with my dealer to resolve.

I always wanted a Kubota and do love this little machine for what is is. But having a machine I cannot rely on is a real issue.

I am wondering if the collective can provide some thoughts or input on where I go from here.

TPS does not make sense at all. My first impression is that it is a fuel issue. Try unscrewing the fuel cap when this happens and see if it will start.

quote:

Originally posted by Shifferbrains:
TPS does not make sense at all. My first impression is that it is a fuel issue. Try unscrewing the fuel cap when this happens and see if it will start.

This would be my guess also, sounds like the engine is getting vapor locked. Removing the fuel cap to vent the pressure in the tank may fix the issue.

sounds like vapor lock, but 80 degs isn't all that hot. Weak fuel pump? Compromised fuel filter?

Thanks guys, I will try the cap thing tomorrow. Could be the fuel pump. There is no fuel filter.
How can one test the fuel pump?.

quote:

Originally posted by old rugged cross:
Thanks guys, I will try the cap thing tomorrow. Could be the fuel pump. There is no fuel filter.
How can one test the fuel pump?.

Fuel pressure gauge on the fuel line after the fuel pump. Change the filter if you haven't in a while. Also check and see if any of the fuel lines are very close to hot areas of the motor or exhaust.

First thing I thought while reading the OP was vapor lock. Fuel pump or filter.

quote:

When it sits in the sun and the ambient temp rises to 80 degrees or higher it will not start.

Vapor lock was my first inclination. Based on the symptom, it sounds like the sun could increase the temperature in an area where the fuel line is routed. A quick test would be to park it in the shade on a hot day and see if the symptoms are the same. If so, then it could be a simple as opening an engine cover when parking in the sun. A PITA to be sure but way better than spending $1200.

BTW, any of us that thought of vapor lock are either 1) way old (like me) or 2) work with carbureted engines on a regular basis.

I was thinking fuel issue as well. Other than a true vapor lock, I have seen a plastic fuel line collapse when it gets hot. This would be before the fuel pump, the pump pulls the hose closed, preventing the free flow of fuel.

I agree that 80˚ seems not "hot enough" to cause this kind of issue, but if it is in direct sunlight the surface temperature could be much higher. Have you considered that it might not just be heat in general, but the sun shining on a specific part of the machine that causes the problem? If so, a workaround presents itself, park it so the fuel system is in the machine's own shade, or rig some kind of a parasol.

One other thing to check, given that you don't have a fuel filter, there may be a filter on the end of the fuel line inside the tank to serve as such. Sometimes these get clogged although I don't see this related to heat. Worth a check any way. Fish it out the filler hole with a bent coat hanger.

I did some internet searching and the fuel filter is an integral part of the fuel pump and not available separately.

Did the dealer say crank position sensor rather than throttle position sensor? The crank position sensor would probably require engine removal to replace.

Are you using ethanol or non-ethanol gas? There's a few threads on tractor forum that describe similar problems:

"This summer it is vapor locking in the afternoon when temperature is in the 90's. Stalls out, engine won't "catch".

It will not start until temp falls into the 70's, then it starts immediately and runs fine."

The problem seems to be bad fuel ruining the fuel pump and the solution seems to be cleaning the fuel tank and replacing the fuel pump.

Sorry, I don't have first hand experience.

Thanks guys, I really appreciate the thoughts and suggestions.

I do not run much fuel through it. But mostly use E-O fuel as that is what I usually keep on

I too believe it to be fuel component related some how. I pulled out of my shop this am. Snapped to life with the turn of the key as usual. Having it sitting outside now. Once temps rise, going to be hot today I will check it. Surely it will do what it always does. Try to fire upon a turn of the key but will instantly die. Pumping the throttle has no effect. Then it will just crank. If I let it sit for a while and try again. Same outcome. It will try to start once when I first try. Then it will crank but will not attempt to fire.

Thinking about it, it could also be an electrical component that when it gets too hot, it stops working. Maybe the coil. After loosening the fuel cap and seeing it that works, pull a plug wire and turn the motor over and see if you have spark.

I don't know what E-O fuel is.

I won't conjecture what the problem is, but as different thing, I'd like to recommend that, since it seems you don't use it a lot, and I may be wrong with that assumption, once you have it running, I'd burn up all the fuel out of it and get it as low as you reasonably can, then fill it with fresh fuel.

Where I live, we have Ethanol 10% mix fuel and we have lots and lots of 100% Pure Gas, no ethanol.

The ethanol blends ruin rubber gas lines and the innards of carbs. You may have an issue with this, not counting your current dilemna.

If you have it available, buy the 100% Pure Gas, no ethanol blend.

Good luck to you, best wishes.
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Could it be getting hot enough to weaken springs or sensors and trip the automatic choke?

quote:

I don't know what E-O fuel is.

Ethanol free fuel.

Where's PHPaul when we need him?

When it won’t start try cranking it with some starting fluid. At least if it runs on that you know it’s fuel related and you’ve narrowed it down some.

Not sure your location but here in the north winter fuel is blended to have a different vapor pressure than summer fuel. Winter gas would be more likely to give you vapor lock issue than summer fuel. If you’re still working thru winter gas in it that might be the problem

My guess, and it's only a guess, is that there is a temperature sensor that failed or is failing. It would control the injectors fuel rate and is not giving it enough fuel. Does it restart after it is warmed up, as in turn the key off and restart within a minute?

ok guys, some really great discussion.

I was a little low on fuel. There is no fuel guage which has always been a head scratcher for me. I keep fresh fuel and treat all my fuel.

Today it did start after being in 90 degree direct sun. This is a bit sporatic. Petr, that is really interesting. I would say yes, that has been an issue. Today it was not. I need to keep testing it. Tomorrow is supposed to be pushing 100 degree's