Posted this in electrical tech as well but figured i would post here also since my bike is most closely related to an EVO FXST.

Bike is a 2007 Ultima Fat Bastard 250 (kit bike) which is based on 93-99 FXST. Carbeurated 113 ci Ultima and 6 spd trans. Was cruising down the interstate at 75 mph when she started sputtering and would bog under throttle. Reached down and switched to RES cause I thought that might be the problem. That didn't help so I limped the bike to a rest stop which was about a half mile up the road. When I parked, it was idling fine but as soon as I gave it throttle it would bog and sputter. I shut the bike off and went to restart it, and nothing...No lights, no nothing. Wondering if anyone has any ideas of what it could be?

I already know I now have to replace the battery because it is only showing 10.5 volts after being on a tender for 2 days.

Mechanical linkage to the carb is fine and the slide operates normally.

 

Before you shut it off did you have lights?

In the electrical section is a couple really good posts about diagnosing the stator and rotor, as well as the voltage regulator. I would check all of those out and see what you find.

 

Actually you need THIS THREAD and THIS THREAD from the Electrical DIY forum.

 

Thank you!

 

Run a jumper to the coil and see if it starts. If it does then work backwards till you find the problem. I would look at the main breaker, ignition switch, run/stop switch and also see if it's charging.
john

 

At this point just replace the battery and see what you have....newer sealed battery's tend to die a sudden death with little or no warning. My last "Harley" brand battery served me well for years, but when it died it turned off like a switch....no warning, just quit working...wouldn't charge at all. I bet if you put a load on your 10.5 volt battery it will drop to zero... which equals no lights. Also if the battery drops to 0 volts the charging system will not charge at all...it requires some voltage to "excite" the circuit or it will not work.

 

I'll pick up a new battery tomorrow and see what happens. Hopefully, that will fix the issue and I will be back on the road in short order. Thanks again!

 

After the new battery and before you ride anywhere, check the electrical system output. I have some directions here somewhere, but a quick check is to start the bike with the headlights on and check the voltage across the battery. At, say, 1500-2K RPM you should have >=13.5V.

Batteries do just die by themselves, but they get killed by dead charging systems too. Also, a "tender" may not charge a dead battery.

 

Either you had a ground wire come off somewhere or your charging system just **** the bed

 

Well, there ya go! Replace the battery and check out the charging circuit. My 07 Ultra's voltage regulator quit on me and the battery was due to be changed as well. Yours is about the same age.