Meeners 2008 KTM 250 sx Supermoto Build - Two Stroke Power
Engine, Drivetrain & Transmission, Cooling Mods
-- Stock 36mm Keihin PWK Carb Tuned by KRW Cycles
-- FMF Expansion Pipe & Spark Arrester
-- 520 116 Link EK O-Ring Chain
-- Motorex Top Speed 15w40 Synthetic Gear Oil
-- 13T & 14T Renthal Steel Sprocket, 42T KTM Rear Sprocket SM / 52T KTM Rear Sprocket Dirt
Air & Fuel Modifications:
-- Jetting; __ Pilot Jet, __ Main Jet
-- Running 40:1 Champion Water Pumper 2 - 2-Stroke Oil
Brakes, Wheels, & Suspension:
-- Dirt/Street Wheels: KTM 21"F & 18"R w/ __ Knobbies
-- Track Wheels: KTM/Behr 450 SMR 16.5"x3.5" & 17"x3.5 Fronts & 17"x5" Rear
-- Track Tires: 125/80/R420 F & 165/55/17 Metzeler K1 Racetec Slicks (120/70/17 Dunlop KR106 Slick on 17"F)
-- Big Brakes: Beringer FTE 4-pot Radial Caliper and Master Cylinder from 2006 KTM 560 SMR w/ Purte1 Radial Bracket Adapter
-- Small Brakes: Stock Brembo 2 Piston Front and Brembo Rear w/ F&R Stainless Lines & Motomaster 320mm Adaptor Bracket (Part no. 211012)
-- WP USD 48 mm Forks w/ _ Springs & WP PDS (Non-Linkage) MonoShock w/ Racetech SRSP 6326P15 Serviced by KRW Cycles for 208lb rider
-- Dominus/Motomaster 320mm Floating Rotor (Part no. 111043)
-- Scott's Steering Damper w/ _ Riser/Adaptor
-- Ebay Hour Meter
Appearance & Cosmetics:
-- 10mm Rise 1-1/8 Fat Bars
-- Acerbis Copy Hand Guards
-- Moose Contour Inner Handguard Mounts
-- Skateboard Wheel Bar Sliders
-- KTM Axle Sliders
-- Ebay Peg Sliders
Stage 2: By Late Spring 2013
[_] ASV Brake and Clutch Bar Caps
[_] Look into Flywheel Change depending on if their are issues cornering
[_] KTM Supermoto Specific 14mm offset Billet Triple Clamp
Stage 3: Winter 2013?
[_] Total Loss Battery TRAIL TECH 8 cell battery pack or Batteries (Werker) Plus deep cycle
[_] Upgraded Plastics?
This is the old KTM 300 RIP
Engine Type: 2-stroke
Displacement: 249 cc
Bore x Stroke: 66.4 mm x 72 mm
Engine Features: Single, reed valve, hydraulic clutch
Engine Cooling: Liquid
Carburetor: 36mm Keihin PWK
Transmission: 5 - speed
Steering Rake: (Castor)26.5 degrees
Wheelbase: 58.1 in
Ground Clearance: 15.2 in
Seat Height: 37.8 in
Dry Weight: 210.3 pounds
Fuel Tank Capacity: 1.98 gallons
Forks: 48mm WP USD
Fork Travel: 11.8 in
Shock: WP, PDS No Linkage
Shock Travel: 13.2 in
Wheels: 21" Front & 19" Rear
Brakes: Brembo 2-Piston Caliper & DiskFront, Brembo Disk Rear
380 motor can bolt in with small modification
Swap to sx 125 Triple Trees for Smaller Offset
Suspension Laden/Race Sag is 70-80mm for KTM SM Rear
Static Sag I'm going for 25-30% Adjust rear and match front
Rev limiters are pretty much for 4-strokes and that whole valve thing. Since you have no valves to float, you can rev it till it won't rev anymore. That's the joy of a 2-stroke. You may encounter a point where you loose all power and it feels kind of like a rev limiter. That was actually explained to me by a 2-stroke tuner/guru as a limitation of the pipe and head. I know I don't experience that with a low compression head, but do with a high compression head.
Being "on the pipe" is everything in a 2-stroke. I've found keeping up with the 4-strokes is often very difficult. We may share a similar top end but the bottom end and midrange is non-existent in comparison. They gain in such a major way on corner exit. If you're even the slightest bit off the pipe on corner exit, you loose out to those guys instantly. In some corners I'll end up going wide open before the apex, so by the time I'm at corner exit I'm on the pipe. Nothing will teach you throttle control like a 2-stroke! I take a great deal of pride when I race Supermini to even be able to keep up with some of those guys.
Anyhow, to the original topic question...just be mindful of your downshifts and run a rich bottom end (pilot jet). It may make your bottom end a little groggier, but if you're riding on the pipe correctly you won't even notice it.
I swapped from a 14:52 dirt gears to 14:46 gears for the local cart track. top speed is about 75-80mph.
I race on the stock brakes. I swapped the brake fluid to motul 800 dot 4 as it has the highest boiling point of any fluid available to me. I'd reccomend going with bigger rotor and caliper, but mine raced okay with the stock setup.
Other suggestions for you? If you plan to race that bike you are going to need to get the suspension revalved if you want to be competitive. if you are just riding for fun, then have at it. It's a blast to pass the 4-strokes on a smoker.
Oh, and try this jetting: 40pj, NAFH needle in the 3rd or 4th clip position and a 162 or 165 main. It'll rip your arms off on the road and allow you to run with the 450s. PArt of the reason I like this jetting is that the richer PJ keeps you from seizing the engine when you are blasting at 70 mph and then close the throttle and let it coast to a stop. If you run the stock 35PJ and do that you risk seizing the engine.
380 models with the 50mm extreme forks (98 and 99 models) have 17 mm axle diameter
380 models with 43 mm upside down forks (2000, 2001, 2002 models) have 20 mm axle diameter
if you use a 48mm fork of a newer model (the newer the better ) then its 26mm axle diameter. we use such a fork (and we also have to use other triple clamps).