Hey Malves, love it when a plan comes together. Glad to hear you EFI is running sweet. When they are dialed in they are such a pleasure. Purr like a kitten around traffic and roar when opened up.

I changed my final drive this afternoon, from 15/42. I put on the 39 rear sprocket that I got from Joel, combined with a 15 front. Just got back from a test run up the mountain and down along the coastal flats. Love it. I was overreving and shortshifting as the power dies at 8000, now there is a lot more usable power with the taller gearing. I mistakingly went the low gear route, right down to 13/48, looking for power, only to end up way past the power curve. 15/39 forces the engine to stay slap bang in the middle of the action. Not sure if this combo will work on a 250, but 331 and up, perfect.
I would guess at 14/39, for a modded 250.

 

I run the stock 14/39 gearing. Been thinking on trying a 14/42, but I am afraid I may regret it. Maybe try a 13T first and see how I like it.

Exactly how my bike sounds. I'm telling you...I love the Powercore sound. Down here I ride lane splitting 98% of the time...I certainly can have their attention when I need to.

 

I put a 13T (13/39) on for about a week. Very difficult doing racing starts off the line.....front end was up in the air all the time!! Gears ran out to quickly to utilize the power. It was kinda fun for a week.

I like the 14/39 combo, it feels good off the line & will loft the front wheel off the throttle in 1st easily & in 2nd without the clutch (bit of handlebar yank needed tho). Good torque thru the gears on the mountain circuit!

I've had a 15T sitting in my toolbox for 5 months now & never felt inspired enough to bother bolting the bugger on. I'll give it a go next week Graham.

 

That´s a good thing, then... No?