The Fastest YZ125 Ever? | Project Bike - Pro Circuit Yamaha YZ125 7

The legendary YZ125 has been in production for 51 years, earning a special place in the motocross community thanks to its longevity and the pure joy it delivers on the track. It’s the perfect stepping stone for young riders transitioning from 85s who aren’t quite ready for a 250F, and equally ideal for adults who simply love wringing every ounce of performance out of a bike. A few years back, I had the pleasure of helping develop the latest generation of the YZ125, which came with updated bodywork, refined suspension, and a new carburetor. Recently, I took a brand-new stock model to my home track at Glen Helen Raceway to refresh my memory of how it feels in stock trim—then brought it straight to Pro Circuit Racing to prep it for the upcoming 2-Stroke Nationals. The crew at PC turned it around in under a week and had me back on track just seven days later to shake it down and compare it to the stock version.

A few years ago, the Pro Motocross Series featured 125 All-Star races as a halftime show during select Nationals. None other than Ryan Villopoto—the greatest retired rider of all time—lined up aboard a Pro Circuit–built YZ125 and put in some impressive performances. While still at Yamaha, I got the chance to ride that engine spec myself, even throwing a leg over a cylinder hand-ported by the legend Mitch Payton. Fast-forward to today, and Mitch has continued improving that engine package, claiming to have found even more horsepower—which had me pumped to get on this updated beast. PC’s recipe includes a ported and polished cylinder, piston, GET CDI, VForce reeds, a full PC exhaust system, and a mix of VP MRX02 and C12 race fuel. We also bumped the rear sprocket from a 49 to a 51 for added low-end grunt and throttle response.

Click play to hear and see this bike in action and listen to Tokarski's thoughts.

Build List - 2025 Yamaha YZ125 Project Bike

Engine:

• Pro Circuit Works pipe: $306.95

• Pro Circuit R-304 silencer: $171.95

• Cylinder and head modification - Pro Circuit: $349.95

• Pro Circuit YZ125 "RV" spec piston: $258.50

• GET CDI unit: $585.95

• Pro Circuit GET remap: $99.95

• GYTR YZ125 jetting kit: $99.99

• MotoTassinari VFORCE4R: $168.00

• Total engine package price: $2,041.24

Remainder of build:

• Enzo Racing - suspension revavle, respring, and spring tube kit

• VP Racing - C12 and MRX02 fuel

• Hinson - Complete billet clutch kit

• Works Connection - Pro Launch device, Engine plug kit, and Brake caps

• Dunlop - MX34 front tire and MX14 rear tire

• Renthal - Twinwall bars, sprockets (13t front and 51t rear), and Kevlar grips

• DeCal Works - Custom graphics kit

• FCP - Titanium engine hangers and titanium footpeg pins

• Maxima - Lubricants

• GUTS - Custom gripper cover

First impressions were immediate—this thing just looks and sounds fast. That R304 shorty silencer adds a high-end feel, and the bike’s bark alone makes you want to go ride. Firing it up, the difference is clear: crisper, cleaner, and more refined than the stock setup. There’s nothing like the sharp crack of a built 125, and just warming it up in the pits put a grin on my face. A few people even walked over just to ask what was done to it. After I gave them the rundown—and told them to ditch their bikes and buy a YZ to take to PC—I headed out for what was sure to be a very fun day of riding.

So, do all the Pro Circuit mods really change the YZ125’s character on the track? Just two corners in, the answer was a clear yes—absolutely worth every penny. Stock YZ125s can be tricky at low rpm, with soft bottom-end power and a need to keep the clutch working. This build completely changes that. Throttle response is sharp, and the torque down low gives you the freedom to ride without constantly feathering the clutch. I could carry a taller gear through corners, skipping unnecessary downshifts and keeping things smoother and faster. Power recovery is quick, and the bike becomes dramatically easier to control—even in soft berms or rough terrain. I expected the low-end improvement, but the midrange pull blew me away. The way this engine screams out of corners and rockets down straights is exhilarating. It pulls hard from low rpm all the way through the midrange and into the top end and over-rev. There’s no flat spot or sign-off—just smooth, linear, and thrilling power delivery.

Jetting was spot-on too, which is impressive considering how sensitive the new Keihin PWK38S carb is to changes in weather, elevation, and track conditions. The bike ran clean all day, even as temperatures climbed. It’s hard to put into words how fun a properly tuned, hard-pulling YZ125 is unless you’ve experienced it firsthand. There are very few bikes that match the fun factor of a crisp, well-set-up 125 two-stroke. You feel like a hero revving it to the moon and getting rewarded with more and more power. Compared to stock, this engine left me with zero complaints—just more power, better rpm control, cleaner running, and more fun. What’s not to love?

At this point, this bike is easily one of my all-time favorites, and I highly recommend that anyone looking to bring more fun and excitement to their riding experience go buy a YZ125 and send it straight to Pro Circuit. You won’t be disappointed. Now we’re taking this ripper to race the 125 Open Pro and +30 Pro classes at Glen Helen’s 2-Stroke National, where it’ll go head-to-head with a bunch of KTM 150s. Even being a little heavier than some of my competition, I have full confidence in this machine. If I don’t win, it won’t be the bike’s fault—it’ll be mine!