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Yamaha’s 2001 YZ250F: The Horsepower Mystery

We will be testing Yamaha’s YZ250F motocrosser soon. Some bikes have already been delivered to customers here in the United States, however, and we have been reading customer ride reviews on the internet for the last couple of weeks.

Recently, FMF Racing posted a dyno chart on its web site showing a horsepower peak for the YZ250F of less than 30 — significantly less than many 125cc motocross bikes (which show roughly 31 to 33 horsepower at the rear wheel in stock condition). Indeed, FMF’s tuned YZ250F had more horsepower than stock, but still less than 30 peak horsepower. Here’s a link to FMF’s dyno chart.

The YZ250F has been hyped almost like no other motocrosser in recent memory. After my interview of Yamaha’s test rider Doug Dubach, I began salivating at the chance to ride the bike — and so have thousands of other dirt bike enthusiasts. Doug described to me the ultimate vet class/amateur race bike with the handling of a 125 and substantially more torque and a broader power curve — all combined with the easier, less tiring power delivery of a four-stroke.

Many people imagined that the YZ250F would have significantly more peak horsepower than a 125 (some expecting it to rival a modern 400’s power), in addition to the broader, smoother power delivery. With all the hype, and nothing to directly compare it to, these people have forgotten that a 125cc two-stroke is this bike’s competition, not a 250cc two-stroke or a 400cc four-stroke. In any event, there has been some disappointment expressed on the internet after the posting of FMF’s dyno chart.

Well, Yoshimura, a company we have worked with before and trust, has now posted its own dyno chart showing significantly higher power figures for a stock and a piped YZ250F. Here is a link to Yoshimura’s chart (Adobe Acrobat). It shows the peak horsepower of a stock YZ250F to be 33.2 — higher than most stock 125cc two-strokes. With the prototype Yoshimura exhaust system installed, the peak horsepower of the YZ250F rises to 35.2 — an extremely healthy figure for racing in the 125 class. More importantly (just as the FMF chart shows), power is much broader than a 125. The Yoshimura graph shows the YZ250F making more than 30 horsepower at all times between 8400 rpm and 13200 rpm — a 4800 rpm spread. Yoshimura’s chart backs up the claim that the YZ250F has extremely competitive peak horsepower, and far better rideability than a 125cc two-stroke.

I can’t explain the dramatic difference in the dyno charts posted by these two companies, but, at this point, I personally believe the Yoshimura chart is more accurate. It may come down to a difference in the type of dyno, or software, used by each company.

By the way, the torque displayed by the 250F on the Yoshimura chart simply blows a 125 two-stroke into the weeds. The YZ250F makes nearly 19 foot pounds of peak torque, and more than 15 foot pounds everywhere between 6,600 rpm and 11,100 rpm — a 4,500 rpm spread. The peak torque of a 125cc two-stroke is roughly 15 foot pounds. A 125 will hold more than 14 foot pounds for approximately 2200 rpm. Trust me, a YZ250F will exit corners far harder than a 125 for virtually everyone — certainly, for amateur riders.