First a little about myself. I did my first motocross race in 1975 in the 125B class. After 9 years of racing (as much as my limited funds would allow) I joined the Marine Corps and didn't own a motorcycle for 22 years. In 2006 my retirement was looming on the horizon and I decided to go back to the sport I loved so much but SO much had changed! I ended up buying a brand-new 2006 KX250F and loved it.
In my first race back (beginner class) I was able to score a come-from-behind win and was asked to not ride the beginner class again. I loved the bike but did not like getting smoked to the first turn, especially on uphill and/or deep sand starts. This led to my next bike being a 2007 KX450F; It was a beast! A holeshot was certain as long as I didn't make a mistake on the line but riding it was like wrestling a water buffalo. I am only 5'7", 153lbs and it was just a big, heavy bike. Next up was a 2009 KX250F that I bought used from a WMX Pro, followed very closely by a used 2009 KX450F. For an entire season I had both bikes and was able to pick either one to ride/race as I saw fit. What I ended up doing was practicing on the 250F (A great way to build skill) and racing on the 450F (A great way to get the holeshot) but even though the 2009 KX450F handled better than my old 2007, it was still a big, heavy beast and sometimes I felt like it was riding me. Because I simply enjoyed riding the 250F more than a 450, my next bike was a 2011 KX250F, the first fuel-injected model. Once again, I loved it and it was to become the platform for my ultimate racer.
Here's the list of mods I did initially:
MB1 suspension revalve
DRD Full Stainless exhaust
TAG Rebound grips
Twin Air Filter
EvoMX Gas Tank Foam
Braking Batfly front rotor
TAG Sprockets (49 rear vice the stock50)
Acerbis skid plate
Pro Circuit 22mm-offset triple clamps
Dunlop Geomax tires
At this point, I was loving this bike and racing it very successfully but I still struggled with starts as I was one of the only guys in my class on a 250F. Furthermore, it made doubles out of tight corners scary, or even impossible in some cases. I did not want to give up the lightweight feel of the 250F but just needed more horsepower to help close the gap. I had previously built a 2004 KX250F for my Son and we added an Athena 290cc big-bore kit. It gave the bike monster torque in the initial portion of the powerband but after that, fell flat on its face and refused to rev. For that reason it was useless as a motocross machine so we sold it to an off-road guy. I heard that a company called Cylinderworks had a big-bore kit that revved like a normal bike so I ordered their 269cc kit and I had it in the mail 3 days later. While I was waiting for a chance to have it installed, I figured that while I had the motor apart I might as well add cams too so I ordered a set of stage2 cams from Hotcams. As luck would have it, I also located a full Hinson clutch on E-Bay for a great price that had only been mounted on a show bike and never used. Add to the list:
Cylinderworks 269cc Big-Bore Kit
Hotcam Stage 2 intake/exhaust cams
Hinson full clutch
Once all of this was installed I was out of time as I had a two-day race, two hours from home. I loaded up both my bike and as a backup my old 2009 KX250F that I had passed down to my youngest Son, as I was not even sure my bike would run properly without anything done to the ECU. Long story short, it ran great during two days of practice and 4 motos, the only glitch was the idle was a bit "lumpy", causing it to stall easily when cold.
Despite the fact that it ran well, I could not help but think a reflash of the ECU would help it run even better. This led to a trip to Tokyo mods, just a short drive away, where for $89 and 5 minutes they performed their magic. The result was an even stronger engine with no more stalling issues. After a couple more sessions at the track I realized that the cams were causing the effects of engine braking into corners to be more pronounced, so to offset that, I simply raised the idle a bit and all was well. The bike is now complete and I couldn't be happier. The only additional thing I am considering is subtracting yet another tooth from the rear sprocket, as the bike has so much torque that I find myself in 5th gear very often on the track and have even tried to shift to a non-existent 6th gear a time or two.
I absolutely LOVE this thing! It has has the light weight of a 250F and now plenty of power to get over any obstacle on the track with confidence. It still won't beat a 450 to the first turn on an uphill or deep sand start but I will be a heck of a lot closer!
The bike is currently dirty in the garage from a practice session yesterday but here is a photo from before the last few mods were done.
Edited by freds4, 09 April 2012 - 07:26 AM.