I thought I would share my experience with installing a 300 crank in my 2014 CRF250L. Before the install the only thing done to the bike was the snorkel was removed and has a K&N air filter. I also have an AFR+ fuel controller. Here is some info on the parts I used. For those that do not know there was a crank recall on the CBR300 which had proved to be beneficial as Honda released a "repair kit" to fix the issue. This kit includes everything you need to swap the crank, with exception to the 300 piston and balance shaft. You can look up the part number to see what is all included. I also decided to upgrade to 300 cams/springs and throttle body. Crankshaft Kit: 06130-K33-305 CBR300R Balancer Shaft: 13421-K33-D01 CBR300R Piston: 13101-K33-D00 Piston Rings: 13010-KYJ-305 CBR300R Intake Cam: 14110-K33-D00 CBR300R Exhaust Cam: 14210-K33-D00 CBR300R Valve Springs Inside x4: 14761-K33-D01 CBR300R Valve Springs Outside x4: 14751-K33-D01 Also used was a 2015 CBR300R ECU from ebay, this plugged directly into the harness and I have not had any issues. The reason to use the ECU us fueling and Spark timing. The 300 ECU appears to advance the timing be approx. 3-4 degrees at idle. I cannot comment on how the curve differs throughout various engine speeds and loads. 2015 CBR300R throttle body from ebay was also used, 38mm vs. 36mm on the 250. I am not going to get into the detail of the install as anyone should be able to do this that is mechanically inclined and has a service manual. There are a few tricky parts being getting the clutch basket off/torqued and balance shaft nut torqued but I made do with standard tools. All the parts were swapped over as described above. While I had the head disassembled I lightly lapped the valves and port matched the intake to the throttle body. Light porting was also done on the intake and exhaust port. Just enough to open up the ports a bit and remove the casting marks. Valves also needed adjusting so this was done at this time as well. Here are some details on fueling. with everything swapped over the bike started and ran just fine. With the AFR+ you have a wideband o2 sensor with a gauge so the A/F ratio can be monitored all the time on the gauge. With no adjustments to fueling the bike has a very rich idle (11:1) but off idle the stock o2 sensor is active and closed loop control is utilized keeping A/F ratio right at stoich. I will continue working to figure out the rich idle. While riding, the bike utilizes short term fuel trims to achieve stoich. The ECU appears to target stoich in all low to moderate load cases. In high load cases the bike switches to open loop and the stock o2 does nothing. At full throttle the bike was also running in a rich condition. At mid-range rpm A/F would be at 12.5:1 while at high engine speed A/F would be around 11:1. And the part everyone is interested in........Performance. With the stock exhaust on the bike engine torque had a significant increase in the low to mid range of the RPM range. It is hard to describe in words but I would say somewhere in the ballpark of 20-30% more low to mid range torque. Since I mostly ride on the street I changed the front sprocket to a 15t and the rear to a 39t. With the 300 swap the engine pulls harder with the taller gearing than the 250 did with the stock gearing. Acceleration is much improved. As for top end power the best way to quantify this is top speed. The 250 would top out right around 70 mph indicated on GPS on level ground. Going up hills it would slow down to 65 or so. With the 300 upgrade speed was increased 10 mph up to 80 mph with less speed lost going uphill. With all this done I felt the stock exhaust was holding the bike back in the upper rev range. I installed an FMF Q4 with power bomb header this morning. Took the bike for a ride and definitely noticed an improvement in mid and top end power. The A/F ratio confirmed what I felt as A/F ratio at full throttle increased 1 full point from 11:1 to 12:1 indicating increased airflow through the engine. This is still a bit rich but safe. I leaned out the ratio from 12:1 to 12.5:1 and 13:1 with the AFR+ and did could not tell a noticeable difference. I anything I think it likes 12:1 to 12.5:1. Better rich than lean. Top speed is now 83-84 indicated on GPS. The bike will comfortably cruise at 70-75 mph with the taller gearing. I might take a look at increasing flow area in the intake on the side of the air cleaner cover or where the snorkel was located to see if that is creating a bottle neck. My guess is that head porting/cams and valve springs are now the limiting factor. The bike definitely looses power as you approach the rev limiter. A look at a CBR300R dyno graph confirms this. I think the gearing on the bike is about perfect for the road, top speed is about the same in 5th and 6th. However engine revs are obviously much better in 6th. Hopefully this was informative, also the cost is very reasonable to get the crank kit Honda released for the 300 crank recall, $220 from bike bandit. Like I said in the beginning it come with absolutely everything to change a crankshaft ( crank, gaskets, O-Rings, piston wristpin clips, header gasket, keys for crank/balance shaft, valve cover gasket). I's sure I am missing things but any consumable used during a crank swap it comes with. I have not done the math but I am sure separate you are saving over $100.