The Yamaha YZ250F was the first quarter-liter four-stroke, and as such, it had a long string of firsts. First 250 four-stroke to win an international race, first to score an AMA Supercross win and championship title, and first to win an AMA National race. During that time it’s gotten nearly continual tweaks to add power, and also make it easier to start and more reliable. But it’s also remained remarkably similar to the original design, and there are some who think it’s about maxed out in its current configuration.

During nearly that entire time, Luc “Frenchie” was working with either Yamaha of Troy, or the Yamaha Factory Team, tweaking and tuning to get the maximum out of the 250 engine. In short, he definitely knows how to get the most out of the blue 250s. We decided to let him do some maxing of his own, and you’ll find the results below.

Video: Maxed Out, C4MX Yamaha YZ250F

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Luc "Frenchie" Caouette got started in Eastern Canadian motocross by wrenching for Marco Dubé, and then working for the Two Wheel Kawasaki team, with Sean Hamblin. Along the way he learned English, as well as a ton about both engine and suspension work.

After passing a resumé to Erik Kehoe at Binghamton in the summer of '01, he got a call telling him that if he could get his work visa figured out, he had a spot at Yamaha of Troy. After dialing in those details, he joined the team late that year.

Click any image for a larger version.

With the combined efforts of Dave Dye and Frenchie, they dialed in the engine and chassis on our 2010 YZ250F, and the result was one very sweet-looking and performing bike. The good news is, all of these will work just as well on the 2011 model. Custom graphics for this one were courtesy of N-Style. Visit their web site or call for pricing.

A test rider to wring out the bike? Those chores went to Austin Politelli.

So what went into the engine? You name it, and it's in there. Starting on the intake side, with a Twin Air flow kit (filter and billet cage, $150), as well as a different air boot that flows better and adds half a horsepower by itself ($55). There's also a carb mod ($150) combined with a float bowl change ($85) designed to eliminate any bogging on hard or flat landings. There's also a replacement needle ($25), as well as a different carb bore ($115), which adds mid-to-top power, and is recommended for MX only.

From the top down? There's a new spark plug ($14), and custom billet cams ($690) designed to boost bottom-to-mid power. They're mated with a Faction MX valve spring kit ($315). Frenchie really wants to make sure that there's no valve float, especially with a higher rev limit (from 13,500 to 14,200 RPM) provided by a JD ignition box ($650). As for the valves themselves, they're Faction MX high-compression one-piece valves ($885), and mated with DLC buckets ($500) for less wear and friction.

As for the head itself, it gets the porting treatment from C4MX ($400) for better flow, and for added life and better flow, it also gets copper valve seats and a five-ange valve face ($650).

Moving into the cylinder, you get a high-compression piston ($275), and DLC-coated wrist pin ($115). They're connected to the lower end via a stronger-than-stock Carillo rod ($280), and a C4MX crankshaft mod ($500) that makes it lighter than stock, and eliminates the counterbalancer and rebalances the crank for much snappier throttle response.

C4MX also eliminates the oil tank and lines with their oil tank kit ($140). To make shifting easier, reduce friction between the gears, as well as reduce heat and add more power, the transmission gets and ISF (Isotropic Superfinish) process to smooth everything out to factory standards ($400).

To finish it off the internals, and make sure there's no slipping and loss of power, there's a complete Hinson clutch setup, including the basket (H341 $289), inner hub (H142 $309), pressure plate (H070 $189), clutch plates, including fibers, steels, and springs (FSC141-9-001 $199), and a Hinson cover (C141 $159.99).

The exhaust? That belongs to FMF, and is one of their Factory 4.1 systems ($849).

Radiators are stock, but to keep things run cool under pressure, Frenchie bumps up from the stock 1.1 psi cap to a 1.8 psi cap ($37). Oils are from Maxima.

With the oil tank eliminated, and some high-digit components in the engine, a Works Connection skid plate seemed like a good idea.

One of the goals of Frenchie's engine package was to add some more low end power. Yamaha boosted that in the 2010 model with the D-shaped exhaust port, but like most things, more is better. You can see that Austin was able to put it to good use.

The stock sprockets were replaced with Renthal components ($25 front, $65 rear), along with an RK chain ($116). Black Excel A60 rims were used front ($200) and rear ($230). The black finish? That's all for fashion, but the wider 2.15 width in the rear? That's to make sure it hooks up, along with the Dunlop treads (see your dealer for pricing).

The stock bars were swapped out for a pair of Renthal Twinwall bars ($120), and the stock clamps were traded out in favor of these XTRIG clamps ($800) that feature adjustable offsets, PHDS (Progressive Handlebar Damping System) mounts, multiple bar mount options, precise clamping, and flex tuned for a particular model.

As for the front suspension, the economy may be bad for some factory technicians, but it works out pretty well for consumers. C4MX has access to some former factory talent, and the forks were revalved ($180) and set up for more aggressive riding. Austin dig the action, both over braking bumps and the bigger jumps.

The rear shock also got a rebuild from C4MX ($180 plus oil and springs), and we really liked the addition of the XTRIG Preload Adjuster ($150). With this one you'll never need a hammer and punch to change your shock spring preload. Instead, an 8mm wrench is all that's needed to raise and lower the preload adjuster all the way up and down the shock body. Very cool.

Austin was having fun on the bike, and putting in some long motos.

Controls? Renthal's long-lasting Kevlar grips ($20) were used, along with a Works Connection Elite Perch and lever ($140).

Meanwhile, Austin was still styling and having fun. He was impressed with the power of the bike.

The engine got a little dressed up, courtesy of a set of Works Connection engine plugs ($40). The fuel? That was Renegade's SX4+ ($38/gallon). Yep, that's pricey for regular racers, but it's a favorite of the GEICO Powersports Honda, DNA Shred Stix / Star Racing / Yamaha, Suzuki City and Honda of Troy teams, as well as riders who race stock classes. Developed for high-revving two-strokes, it's said to be more stable and cause less issues with gumming than other racing fuels. For those riders who need to worry about such things, it's also AMA-legal. This came highly recommended by both Dave and Frenchie. For a less expensive alternative, Renegade's MX4 ($15/gallon) doesn't require jetting changes, also doesn't suffer from gumming issues, and allows riders to easily switch from pump gas to race gas.

If you're going to make it go, you also have to make sure it'll stop, and a QTM Oversize Front Brake kit ($300) handles that chore. This is the same type kit that Chad Reed recently chose when racing his Vodaphone Honda in Australia.

There it is, the finished YZ250F, and one that wouldn't make you feel like you'd brought a knife to a gunfight, no matter the level of competition. While this one was maxed out, with just about everything possible thrown at it (and it might max out your credit card), C4MX also has engine packages of varying degrees available. Checking in with Frenchie to let him know your requirments (and budget) will yield plenty of options.

Contacts: (Engine and suspension mods) (Clutch components) (XTRIG clamps and preload adjuster) (Oversized front brake kit) (Exhaust) (Skidplate, clutch lever, and engine plugs) (Bars, sprockets, and grips) (Air filter and cage) (Rims and chain) (Tires) (Graphics) (Lubricants) (Fuel)

2011 Yamaha YZ250F.

While the project bike here was a 2010 Yamaha YZ250F, everything you see here will work just fine on the 2011 as well. Once again, this warhorse features the same engine package, and the bilateral beam chassis that was introduced in 2010. But this one gets a new intake boot, carb settings, and clutch pull. There’s also repositioned radiators, and oil tank, in an effort to centralize the mass.

2011 YZ250F Specs

Engine Type: 250cc liquid-cooled DOHC 4-stroke; 5 titanium valves
Bore x Stroke: 77.0 x 53.6mm
Compression Ratio: 13.5:1
Fuel Delivery: Keihin® FCR MX37
Ignition: CDI
Transmission: Constant-mesh 5-speed; multiplate wet clutch
Front Suspension: Speed-Sensitive System inverted fork; fully adjustable, 11.8-in travel
Rear Suspension: Fully adjustable single shock; 12.0-in travel
Front Brake: Hydraulic single disc brake, 250mm
Rear Brake: Hydraulic single disc brake, 245mm
Front Tire: 80/100-21
Rear Tire: 100/90-19
L x W x H: 85 x 32.5 x 51.3 in
Seat Height: 38.9 in
Wheelbase: 57.7 in
Ground Clearance: 14.8 in
Fuel Capacity: 1.7 gal
Wet Weight*: 224.8 lb
Color: Team Yamaha Blue/White; White/Red

* Wet weight includes the vehicle with all standard equipment and all fluids, including oil, coolant (as applicable) and a full tank of fuel. It does not include the weight of options or accessories. Wet weight is useful in making real-world comparisons with other models.

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