( 3) Flywheel weight. We ran a 9-ounce Steahly flywheel weight. We loved what this mod did for the chassis as much as we loved what it did to broaden the power delivery. Once we installed the flywheel weight, the Pro test riders returned to the stock mapping because they could let the weight mute the bark instead of the ignition. It should be noted that we had issues with the press-fit of our prototype Steahly flywheel weight; Steahly had to redesign the mounting system. You can contact Steahly at www.steahlyoffroad.com or (800) 800-2363. ( 4) Exhaust. The stock YZ450F muffler is very choked down. It has grown 2 inches longer while being squeezed down from 33mm to 30mm since 2011. The combination of a longer canister and smaller core slows the revs down, hampers throttle response and delays the transition across the middle to the top. Q: HOW DOES IT RUN ON THE DYNO? A: It is better on the dyno than it is on the track. Max horsepower is 55. 24 ponies. That is a very good peak horsepower number, but, strangely, the dyno numbers make you think that the engine favors high-rpm, top-end attacks. Not so. It is a low-to-mid powerband on the track. Q: HOW DOES THE 2013 YZ450F HANDLE? A: It’s far from perfect, but, not surprisingly, the MXA test riders have issues with the handling of the majority of 2013 bikes. Most test riders complain that the YZ450F front end is loose on the entrance to turns and then lifts on the exit. The effect of the light front end at the crux moment of cornering causes the bike to step out when it should be going forward. It likes sand, berms and good dirt. It doesn’t like flat turns, ruts or mud. It is not a scary bike to race—just irritating. This is nothing new. Before the advent of the backwards-engine design in 2010, the 2009 YZ450F pushed in the center of the corner (as opposed to the entrance). Our fixes all revolved around balanced power, balanced suspension and a balanced chassis. Q: WHAT DID MXA CHANGE ON THE 2013 YZ450F TO IMPROVE HANDLING? A: We think our engine mods go a long way toward calming down the chassis, but we have tested a potpourri of frame and chassis mods. Here is how we rate them. (1) Shock linkage. By swapping out the stock rising-rate linkage for a longer Pro Circuit arm, we lowered the rear of the bike, which allowed a wider range of setup options in terms of fork height, race sag and suspension settings. For more info, go to www.procircuit.com. ( 2) Front brake. Yamaha’s front brake is adequate, but not much more than workmanlike. We swapped the stock 250mm front rotor for a 270mm oversize brake kit. ( 3) Engine relocation kit. Moving the engine forward puts more weight on the front wheel to help the front bite. A cheap solution is to move your rear axle as far back as possible. This also moves the engine’s weight bias forward. ( 4) Radiator lowering kit. Surprise! Test riders could feel the difference and liked it.
Left-handed compliment: We geared the YZ450F down, but
not to make it hit harder, but instead to get to third sooner.
Slant nose: We have no complaints with the engineering on
the backwards engine, but wish it had a broader powerband.