My 250S FI is acting up.
I am just guessing in the wind, too many wires everywhere.
Here is the symptoms-
-Starts great!, (cold start) then rpms slowly fall off until it stalls (aprox 1 minute duration)
-Can restart with a little throttle, if hot start - it will not start (almost starts though)
-Some backfiring
-Hesitation, stalling, more hesitation when goosing throttle, quite a bit as the engine warms up
-At 5-6k rpm a lot of power is missing, not a smooth running, like the timing is too far advanced?

-I have pulled the air cleaner foam out
-I have pulled the spark plug, looked fine
-I have pulled the ecu out and checked for corrided terminals
-I have checked to see if coould pull codes from the orange black wire, just 20 short flashes. No FI light on in general unless I pull a senser.
-I pulled the tank off and inspected hoses for cracks, put back on
-I changed the fuel twice
-I put in a different ecu (programmable) same symptoms.

Anybody have any ideas for me too check, when it gets warmed up it is acting up. Almost like the mixture or timing is wrong.
Thanks in advance for any replies.

 

check for air leaks

like the boot the throttle body mounts to

 

Like PB said-make sure there are no simple mechanical issues.
If no signs then based on the symptoms the throttle position sensor may not be sending a linear signal to the pcm. Intermittent problems almost always require some means of monitoring the suspect signal with a DVM or a scope. Sucks, but that's the reality of computer controls-and patience or money to throw at parts.

 

Try opening the fuel cap & closing it a few times while bike is warming up. There can be a pressure lock or vacuum in the FI tank sometimes. This normally stops my bike starting in the few occasions it has effected me but might be worth a try.

 

Just addressing off your first point, try turning the idle screw up some and see what happens. My RPM's start high from a cold start and slowly go down as it heats up. (I'm assuming a computer controlled choke function)

Doubt that would solve the other problems. So prob not that. But anything might be worth a shot at this point.

 

Thank you for the replies, I'll get some free time on Monday to work on it again. I have fiddled with the idle screw (didn't help), I can't remember if I tried with the gas cap opened, so I'll try that again, and check the throttle body for air leaks too.
I do have a pdf manual that describes how to check the sensors on the klx250s (DFI). Not sure if I have a digital meter around. The one sensor on the tail pipe is the O2 right?, I think I want to check it since that heats up pretty darn quickly the same time as the problems start. Anybody know are the sensors generic, or do I need to order from dealer if it has a fault. Thats interesting about the choke, so maybe a temperature sensor? Would that be a engine temp sensor not telling the ecu to signal servo to close/open choke?

I think next motorbike I buy will be old school, but modern. Forget the computer unless you can hook it up to your smart phone with a regular charging usb cable, and get a read out of every thing the computer gets maybe with possible limp home mode on the app that can reconfigure the map and stuff.. :-)

 

Spent some more time on my bike today. I got nowhere. Followed manual to check crank shaft sensor, and checked timing with timing light. I posted earlier, but I had my multi-meter on wrong setting. So I was a fool. The sensors I check were all ok at the end.

So I still have same problem, but I noticed it does not happen if I lean bike to the right. If its standing up or on the kick stand or leaning left the problem happens. Just when engine hot straight up, and worse the farther it leans to left. The more on its left side the worse the hesitation, back firing....

I want to check the bike down sensor next. Any thoughts?

 

Sounds like fuel starvation. I would disconnect all hoses at the carb/FI unit and check that the fuel from the tank is flowing freely with the pit **** in all positions except 'off'.

 

I don't have a petcock valve. No reserve, no on/off. The fuel pump is inside the tank and as far as I am aware has a filter that can not be accessed. I wanted to take injector off but the bloody screw is on so tight I am afraid I will strip the grooves on the screw's head. (phillips)

I did take the tank off once and blew compressed air around. You are probably right about fuel starvation. Maybe its the fuel pump inside the tank. I think I can remove it from the bottom, but not sure if its user serviceable.

 

That injector screw is crazy tight. I stripped mine trying to get it off.