The 250es and 250sx motors are 100% interchangeable and the gearing differences in the transmission is minimal and is barely noticeable when riding..
I installed a NOS 250SX motor in my ES then had fun with it..called it my 'Back in Black' build..
For me it took away a bit of take off torque, about the same as someone switching from stock size tires to 26". If you're considering a 250ES motor in your frame it will be the opposite..you'll gain torque and lose a small amount of top end speed. Oversize the rear tires one size to bring it back to stock ratio.
My ride isn't as pretty anymore since this was a few years ago..but they never are when you ride them where I do. But at least I have my memories of how pretty she was..
It'll work..go for it!!
Last edited by dougspcs; 03-20-2016 at 08:24 AM.
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)