Yamaha YZ125s are great bikes but have been basically the same since 2005. For this build we thought we would see how good we could get this 2011 YZ125 that was saved from a premature death. The bike had been rode hard and was pretty beat. The cylinder was in bad need of full repair from Millennium and the bottom end was no better. 

Jay Clark thinks it’s good to build some of these Craigslist finds as cheaply as possible (the bike was only $800), however, for this build Jay thought why not go all out and build a full-on race ripper motor with the help for two-stroke guru Tom Morgan. Tom worked for factory teams and top racers for years and has long been the choice of top two-stroke engines. So we shipped off our engine to Tom and we tackled the suspension and chassis part of the build.  

The YZ134cc still sounds like a 125cc and produces more mid-top HP while maintaining a normal type power band. This power works well for use on longer, faster tracks. The YZ134cc is a standard bore stroker; TMR strokes the crank and leaves the bore stock size. The cylinder port timing and head dome shape and volume are modified to achieve the desired performance with the stroked crankshaft. The piston is modified to add a boost port of the correct open duration to further improve performance. The crankcases are also modified for clearance to the stroked crankshaft and other changes to produce the correct power output. The motor also has a balanced crankshaft from CWI to help on vibration and of course to change the stroke they have to modify the pin placement. 

After throwing way too much money at this thing we have the ultimate fun machine that is great for a young rider or an older guy who wants to relive his past glory days.

TMR                                   

www.tommorganracing1.com                 
Cylinder porting mod 
Head mod
Piston boost port mod
Case boring, machining, and porting  
Engine assemble 

Hot Rods                                 

www.hotrodsproducts.com          
Complete bottom end kit  
Includes complete crankshaft, main bearing seal kit and complete engine gasket kit.        

Vertex Pistons                  

www.vertexpistons.com    
Pro replica piston kit  (ring, pin and clips). Piston window mod by TMR 

Crank Works INC

www.crankworks.com
Crank balancing and added stroke; added heavy metal to smooth our power and reduce vibration.  

Millennium Tech                 

www.mt-llc.com         
Strip, re-pair damage and re-plate to stock size on the 134cc  

Cometic Gasket

www.cometic.com
Engine gaskets
Reed cage spacer  

Supersprox          

www.supersproxusa.com  
Rear stealth sprocket 49T  
Front sprocket  
Race chain 

Uni Filter                              

www.unifilter.com               
Two-stage air filter                      

Hinson Clutch Components                    

www.hinsonracing.com        
Full clutch kit basket, inner hub, pressure plate and fibers, steels and springs clutch kit and cover 

FMF Racing                              

www.fmfracing.com              
Fatty exhaust                   
Shorty silencer                                     

MotoTassinari                            

www.mototassinari.com       
V-Force reed cages               

Pivot Works                             

www.pivotworks.com                
Steering stem bearing kit       
Swing arm kit 
Linkage rebuild kit

ICW                                     

www.icwbikestands.com   
Radiator straightening and bracing           

All Balls 

www.allballsracing.com
Carb rebuild kit
Throttle cable
Clutch cable 
Brake master rebuild kits  

Renthal                         

www.renthal.com                  
604 Fat bars one 134
Tacky grips
Front and rear brake pads  

Dunlop Tire                             

www.dunlopmotorcycle.com  
MX 3S front  80/100-21
MX 3S rear  90/100-21 

Works Connection                            

www.worksconnection.com     
Elite clutch perch               
Brake caps
Stand
Front brake lever
Brake rotating bar mount
Stand

Tusk                                                   

www.tuskoffroad.com                  
270mm oversized front and rear rotor 
Front and rear steel braided brake lines

Applied Racing                   

www.AppliedRace.com       
Custom triple clamp to fit new fender/number plate

DeCal Works                                     

www.decalmx.com                     
Semi-custom graphics kit                    
Pre printed number plates backgrounds 

Cycra Racing                                     

www.cycraracing.com         
Full update plastic kit in blue 
Formed silicone coolant hoses
High pressure radiator cap 

TM Designworks 

www.tmdesignworks.com  
Chain guide and chain block  

Moto Seat                               

www.motoseat.com                  
Custom cool seat cover

VP Fuel 

www.vpracingfuels.com  
C-12 Fuel 

Faster USA 

www.fasterusa.com  
Complete custom wheel set  

Motion Pro

www.motionpro.com  
Grip glue
Titan throttle tube 

Klotz Synthetic Lubricants           

www.klotzlube.com                
R-50 two-stroke pre-mix

Factory Connection                        

www.factoryconnection.com             
Suspension rebuild and service 

Bolt Motorcycle Hardware

www.boltmotorcyclehardware.com    
Hardware 
Chain adjuster blocks  

Scar

www.scar-racing.com
Titanium footpegs