If you’re a Yamaha YZ450F owner you know that your bike can be a handful at times. If it’s not a handful then you can disregard this test altogether. For me the YZ450F is one of the best bikes in the 450 class for 2025 but it still needs some work to be an easy to ride race weapon. The engine character of the YZ450F is very light/quick feeling. The spool up of the RPM’s is very quick and although at times that is a positive, when the track gets rough and technical that quick revving spool up isn’t a great thing as it makes the bike hard to hang onto as well as wheelies out of corners everywhere. Compared to a KTM, the Yamaha breaks rear wheel traction much easier. So you ay be asking “why not just ride a KTM then Keefer”? Well, smart ass, that’s because the KTM chassis can be somewhat rigid feeling and hard to dial in from track to track so trying to tame down the Yamaha “might” be easier with a flywheel weight.
Why not just use a FX or WR flywheel Keefer? That would be great but they don’t fit or work with the current YZ wire harness. Trust me, I’ve asked Yamaha. What is mind blowing is that no one has made a flywheel weight for the YZ450F to sell up until now. Enter Bundy Built Engines to the chat. Ben Schiermeyer is helping John Mitchell (owner of Bundy Built Engines) and I noticed on his instagram that he was offering 80 gram flywheel weights so I jumped at the chance to try this mod. You will have to mail Bundy Built your stock flywheel then they will weld the weight onto your flywheel and send it back to you.
Compared to the stock flywheel I now have a noticeably calmer engine character build up. There is still plenty of that Yamaha excitement but it is slightly smoother coming out of corners. I think the first thing that the average Yamaha rider will notice is more rear wheel traction out of corners and less “pop” from the front end if your body weight gets shifted too far back on exits of corners. If I start to get fatigued during my moto, this flywheel weight builds RPMs a little more calculated than the stock flywheel does. Another added bonus is that I DO NOT get any added engine braking feel off throttle which made me happy. I was worried that this weight would make the YZ450F feel heavy off throttle but I didn’t notice any of this. If you’re a third gear lugger then the weight will add a little more “chug” or lugability to your Yamaha. I can come into a corner in a higher gear at low RPMs and the Yamaha is not going to stall as easy as it would with the stock flywheel.
If you feel like you can use some more traction as well as a little more control under throttle this Bundy Built flywheel mod is really a must. It’s hard to say that one mod doesn’t have any negative effects on a bike but I truly don’t think this weight has a bad side to it. I think a professional racer or a vet rider can appreciate this flywheel mod. I didn’t get a price on this mod as it is somewhat new to their business but you can reach out to them at 704 662 3333 or head over to bundybuilt.com.
