I have a 2014 xt 250 turns over slow and won’t start. Has new battery
And lots of electrical parts for spark and what not. Just can’t figure out why it’s turning over slow and will only turn over once or twice then I have to let off the starter button and press it again. Does the same thing jumping the solenoid as well. Thanks in advance for input.

There are a couple of simple things you can do to check. You can run jumper cables from a running car (~13.6V) over to your bike's battery terminals. See if that changes your cranking speed. If it does, the battery is most likely the cause. If there is resistance between the battery and starter motor that can reduce cranking speed. On the XT225, the + terminal is accessible on the starter motor. You can jumper cable directly to that terminal and see if the starter cranks properly. The goal is to establish correct power levels in the starter circuit. Another idea is to measure (w/VOM) what voltage is actually at the starter motor. Perhaps someone can weigh in with what that would be on a XT250 bike that cranks properly. This does not address any mechanical issues that might be causing this problem. There could be problems with the motor itself. Both our bikes (2003 XT225) never had any starter motor issues in the 15k trail miles we put on those bikes. I always used Yuasa batteries. Good luck and I hope this helps.

Check battery with multimeter, what voltage is it reading? You say it's new, could still be a bad one or low charge. Mine reads 12.8V, not ridden or charged for a week or so.

Hi Paul - Hope all is going well over on your side of the pond. It would be helpful to know your battery voltage when the bike is cranking. How far below OC (open circuit) voltage it reads gives a better indication of its cranking amp capacity. You are correct in that new doesn't always mean good. Ride safely.

It had a bad ecu when I purchased the bike and the person I bought
The bike from bought a ecu for it and the new ecu it turns over once
Or twice. When I put the bad one on it turns over fine. Gonna check the battery in a bit to see what it’s reading

I'm not familiar with the ECU function on a later model bike. The only thing I can think of is the plug firing is too advanced for some reason. That's an easy thing to check. Just disconnect the plug and see if the engine cranks through the compression stroke. If I recall, some older bikes would slightly retard the spark when cranking. That to avoid a kick back on the kick starter. Not sure what's going on.

OC voltage isn't necessarily conclusive of battery condition. The battery needs to maintain a certain voltage when loaded. I have no specs on that to share. Other than the tests I provided above. Good luck.

If the only thing that's changed is the ECU, that would be the first place I'd look.