Reference this past thread if you would like to read detailed information on riders experience.
http://www.thumpertalk.com/topic/1020420-yz-325/
There is no Replacement for Displacement!!! Repeat those words over and over because once you feel a 325 Two-Stroke Torque (close to a 450) down low, you will kick yourself for waiting to buy the kit! In the FIM World Enduro Championship (WEC) the E3 Class (290+ 2-Stroke or 475+ 4-Stroke) with most of the best riders are on 300 2-Strokes. Most of the time, the 300 2-Strokes will be faster than the E1 250 4-Stroke class or E2 450 4-Stroke class. This kit allows you to have 1 Fun Bike with the Broadest (Linear) Power Band for Motocross/Off-Road riding!
Eddie Sanders Racing (ESR) http://www.eddie-sanders-racing.com/category_s/126.htm
Options: 325 (option-5 Oversize Pistons) (33% Displacement increase over 250) / 345 (option-2 Oversize Pistons) (38% Displacement increase over 250), Aluminum Cylinder (Can be Re-sleeved), Machined Head, Piston, Adjustable Power Valve and Gaskets a $900 to $1000 investment.
Options: Thinking of buying a 2016 YZ250X ($7,390), YZ250FX ($7,890), YZ450FX ($8,890) Model, if you have the money good for you. Or spend the money on a used Yamaha YZ 250 ($3K to $5K), add a skid plate, front disc cover maybe some other preferred items. After riding the YZ ESR 325 I would say, all the 250’s or 450’s are now second rate compared to the YZ ESR 325! I believe ESR is the best VALUE Big Bore with the BROADEST power band!
Yamaha YZ with ESR 325 Kit - (250 was 212 LBS. Dry - 228 Wet) (YZ 325 - 214 LBS. Dry est.)
Weight Benefit over YZ 250FX, (231 LBS Dry est. – 247 Wet or 16 LBS. heavier) YZ450FX (240 LBS. Dry est. – 262 LBS. Wet) – (30 LBS. heavier) (Note: Fuel weighs 8 LBS. / 1 gal.)
Recent Rides: YZ ESR 325
-MX Tracks, torque out of the turn, nice linear power band (easier to ride), stronger than a 250 could ever hope to be! (Yamaha YZ250X or YZ250/450 FX bikes with wider gearing will be at a disadvantage)
-Off-Road (OHV areas), try to stall my bike you may not be able to! Want to ride Trials like for Extreme Enduro, no problem! (YZ 250 (non X) will have less top end)
Setup: Yamaha YZ ESR 325 - 2007 Model
-ESR 325, S7 Woods Porting, Silver Head, Race Gas Dome, (Use Race/Pump Gas 50/50)
-168 Main Jet (ESR recommended Main) and 48 Pilot Jet, Needle in the top position, may go to a 45 Pilot and change the needle position to minimize any unburned oil. Riding Altitude 500’ to 4100’
-Maxima Formula K2 Two Stroke Oil – Flash Point 240 Degrees (One of the Lowest) (helps reduce unburned oil) (40 to 1)
-No Fly Wheel Weight needed, but on the 250 engine a 9 oz. worked well.
-Rekluse EXP Core 2.0 Auto Clutch Kit
Summary: I do not work for ESR, but this bike is awesome! No more 250 for me! Dyno run coming in the future.