Dual Fuel-Injected YZ250F Project Bike

The Yamaha YZ250F has made a pretty big name for itself in the 250 class – it’s consistently won shootouts for the last couple of years with its unique engine design and amazing power. Supercross and motocross star Jeremy Martin has even won two national championships in the past couple of years riding the YZ250F. So what could we do to make a great bike even better? We wanted to do something different than just the typical big bore or bolt-on mod. Our goal was to create a race-legal bike that had serious power, while still running a stock-size bore for the Amateur Mod race class. We decided to hit up a top-level engine builder who specializes in motors for A and B class riders and see what he could do to help us make this awesome bike perform even better. Take a look this video to see the highlights of the build and then check out the post below for more details.

From Good to Better: The YZ Build

Jamie Ellis is a renowned name in motorcycle engine development. He’s is a top-level builder who built engines for Rockstar Suzuki, KTM and more over the years. Last year he branched out on his own and started his own company called Twisted Development, where he applies his knowledge and experience building engines. He got his hands on our YZ and gave it an overhaul any racer would be envious of.

An Engine Overhaul by Twisted Development Drives This Bike

To mod the engine, Jamie ported the head and cut the valve seats. He also degreed in the stage 1 cams and did a custom set up on the Vertex piston. That might sound pretty basic for a good engine builder, but he didn’t stop there. We still wanted more power, so Jamie added a second fuel injector that would allow us to receive continual power at higher RPMs. The added injector sits right inside the modified air intake. The extra injector required specific programming, so we added a Vortex ECU so Jamie could program the engine to perform perfectly. The second injector sprays the precise amount of fuel the motor needs at just the right time to achieve optimal performance for as long as you need.

A Second Fuel Injector Provides Long-Lasting Power

These mods gave this YZ250F some serious horsepower and increased torque – eight more horsepower and three more foot pounds of torque, to be precise. That was massive for this engine. The bike runs a 50 tooth rear sprocket stock but after beefing up our engine the way we did, we are running a 48 tooth now that the motor can pull it. We achieved the big power we were hoping for, but not without a big price tag to go with it. Building a motor like this is best suited for those that are competitively racing the A or B Mod classes, where upgrading to a big bore is out of the question.

Aftermarket Accessories Cover This YZ250F

The stock KYB Suspension is already pretty good, but Factory Connection took a look at it and worked to make it a bit more plush than stock, and help us so we didn’t blow through on the shock as bad. Once they had tweaked it a bit, we felt that it was right on target and was the perfect complement for our new motor package.

Finishing Touches at the Track

When all was said and done, the guys from Motocross Action spent a full day testing out our newly modified YZ250F. They loved it, and wanted to keep riding it as long as we would let them. Check out their article in Motocross Action Magazine to see what they had to say about it!

Products Available at Rocky Mountain ATV/MC That Were Used in the Build

Hot Cams Camshaft (Exhaust) Stage 1 Hot Cams Camshaft (Intake) Stage 1 FMF Factory-4.1 RCT Anodized Titanium Silencer with Carbon End Cap
Hot Cams Camshaft (Exhaust) Stage 1 Hot Cams Camshaft (Intake) Stage 1 FMF Factory-4.1 RCT Anodized Titanium Silencer with Carbon End Cap
FMF Titanium Megabomb Header Pipe Cycra Full Armor Skid Plate Tusk Oversized Floating Typhoon Brake Rotor Kit, Front
FMF Titanium Megabomb Header Pipe Cycra Full Armor Skid Plate Tusk Oversized Floating Typhoon Brake Rotor Kit, Front
Tusk Stainless Steel Typhoon Brake Rotor, Rear Tusk Impact Complete Front/Rear Wheel Kit Tusk Brake Rotor Bolt Kit
Tusk Stainless Steel Typhoon Brake Rotor, Rear Tusk Impact Complete Front/Rear Wheel Kit Tusk Brake Rotor Bolt Kit
Primary Drive Sprocket Bolt and Nut Kit CV4 High Pressure Radiator Cap Twin Air Filter Cage with Pro Flow Intake System
Primary Drive Sprocket Bolt and Nut Kit CV4 High Pressure Radiator Cap Twin Air Power Flow Intake System
Renthal Front Sprocket Renthal Rear Sprocket Renthal 1 1/8" FatBar
Renthal Front Sprocket Renthal Rear Sprocket Renthal 1 1/8″ FatBar
Renthal Dual Compound Grips - Half Waffle 80/100x21 Dunlop MX32 Geomax Soft / Intermediate Terrain Tire 110/90x19 Dunlop MX32 Geomax Soft/Intermediate Terrain Tire
Renthal Dual Compound Grips – Half Waffle 80/100×21 Dunlop MX32 Geomax Soft / Intermediate Terrain Tire 110/90×19 Dunlop MX32 Geomax Soft / Intermediate Terrain Tire
Works Connection Aluminum Radiator Braces Works Connection Elite Clutch Perch Assembly Works Connection Front Brake Reservoir Cap
Works Connection Aluminum Radiator Braces Works Connection Elite Clutch Perch Assembly Works Connection Front Brake Reservoir Cap
Works Connection Rear Brake Reservoir Cap Hinson Billetproof Clutch Cover Hinson FSC Clutch Plate and Spring Kit
Works Connection Rear Brake Reservoir Cap Hinson Billetproof Clutch Cover Hinson FSC Clutch Plate and Spring Kit
Hinson Clutch Basket Hinson Inner Clutch Hub Hinson Pressure Plate
Hinson Clutch Basket Hinson Inner Clutch Hub Hinson Pressure Plate

By Jay Clark