2019 Factory Off-Road Bikes—Nick Burson’s Yamaha YZ450FX

Exploring the Purvines Racing Yamaha YZ450FX war wagon.

The Purvines Racing Yamaha YZ450FX that Nick Burson raced to third in the AMA National H&H Championship is actually a 2018 since IMS didn’t come up with larger-capacity tanks until mid-season—plus it was cheaper to buy leftover ’18s.
The Purvines Racing Yamaha YZ450FX that Nick Burson raced to third in the AMA National H&H Championship is actually a 2018 since IMS didn’t come up with larger-capacity tanks until mid-season—plus it was cheaper to buy leftover ’18s.Mark Kariya

It’s telling that bikes don’t seem to need tons of modifications to run up front nowadays. Obviously, that means bikes are coming from the factory and straight off the dealer showroom floor more capable than ever.

The Purvines Racing Yamaha YZ450FX that Nick Burson rides (as do teammates Tyler Lynn and Axel Pearson) is a great example. Always beautifully prepared by race team manager Collin Woolsey, their looks belie the actual quantity of changes made to the machines.

Perhaps the most crucial modification is to suspension, that responsibility given to Precision Concepts. Galfer brakes and AXP’s skid plate are also plainly visible here.
Perhaps the most crucial modification is to suspension, that responsibility given to Precision Concepts. Galfer brakes and AXP’s skid plate are also plainly visible here.Mark Kariya

Interestingly, the team runs 2018 models owing to the fact that Yamaha actually provides minuscule support. Therefore, buying three (or more) bikes for each of the six team riders from sponsor Berkeley (California) Yamaha was/is an expensive proposition and it made more financial sense to snap up left-over 2018s. Also, IMS wasn’t making larger-capacity tanks for the ’19s until halfway through the season and those, of course, are vital to have in a desert racebike.

From there, Purvines turned to other sponsors to prepare the bikes for the unique rigors encountered in the Kenda/SRT AMA National Hare & Hound Championship Series, presented by FMF, that was one of the series the team focused on this year.

As series runner-up last year and third this year, Burson certainly has credentials. What many may not realize is that he’s an excellent test rider as well, having spent many years in that role for Kawasaki doing new-model development and durability testing. Thus, here is how he’s developed his YZ450FX.

“The motor’s stock—we don’t touch it, we don’t open it up,” he begins. “We just replace the top end after a while [to freshen it up]. Right out of the box, we bolt an FMF pipe on and that’s it for power [enhancements].

“I think we’ve been running stock mapping this year. I messed with the map a little bit [but went back to stock]. Then [we also put in] a Rekluse TorqDrive [manual] clutch. That’s the only [performance] motor parts we use. I’m pretty hard on a clutch so a Rekluse lets me get through the race.”

The sole change to the engine is the Rekluse TorqDrive manual clutch and cover. Otherwise, it’s OEM Yamaha internally to retain reliability, Burson subscribing to the adage that to finish first, you must first finish.
The sole change to the engine is the Rekluse TorqDrive manual clutch and cover. Otherwise, it’s OEM Yamaha internally to retain reliability, Burson subscribing to the adage that to finish first, you must first finish.Mark Kariya

Purvines Racing crew chief Collin Woolsey adds, “They’ll play with mapping depending on the race. Nick did [test different maps] for quite a bit when we first got the bikes. I think he [liked] one up from stock—a little bit harder hit—and he hasn’t touched it since.”

Unlike a number of top pros, Burson isn’t very picky about ultimate power, Woolsey noting, “Nick’s never said [he needs more power], not even once. Nick’s more about, ‘I need to make sure that it’s reliable; when I start it at the start of a race, I need to know it’s going to run the entire race without a problem, no matter what I do to it.’

“So that’s always where my focus is: It isn’t on peak power—it’s on peak longevity.”

To that end, when it comes time to freshen the engines, Woolsey says, “Even when I rebuild them, I rebuild them to stock with stock parts. I don’t use anything aftermarket inside the motors other than the clutch.” Maxima provides all lubricants.

With the dust so prevalent in the desert, nailing the dead-engine starts is a vital component to success, but there’s not much that’s changed on the Purvines machines, Woolsey confiding, “We do put the eight-cell Antigravity [battery] in it, [replacing the four-cell standard unit], but that’s it. It’s got an extra 100, 150 cold-cranking amps to it for initial hit, but that’s all we’ve got. We’ve had a few [starts] that we’ve been caught out on, but there’s not a lot you can do with that. I mean, once you go fuel-injected, you’re kind of stuck with what you get.”

Fasst Company’s unique Flexx handlebar, a GPR V4d, A’ME full-waffle grips, and ARC perch/lever assemblies are clearly shown here as well as the quick-fill receiver on the IMS tank.
Fasst Company’s unique Flexx handlebar, a GPR V4d, A’ME full-waffle grips, and ARC perch/lever assemblies are clearly shown here as well as the quick-fill receiver on the IMS tank.Mark Kariya

Burson continues, “From there, Precision Concepts [dials in the] suspension. That’s one thing we can’t race without.”

Part of that, of course, is respringing both ends for the speeds at which Burson (and teammates) hit road crossings, G-outs, and the like. Precision Concepts determined his bike needed 0.51 kg/mm fork springs with a 5.3 kg/mm shock spring. (For comparison, the YZ250F that Lynn runs in the FMF AMA National Grand Prix Championship Series’ Pro II class features 0.48 kg/mm fork springs and a 5.6 kg/mm shock spring.) Sag is set at 106mm for all team riders.

In the drivetrain, DDC sprockets and RK’s EXW XW-ring chain spin 13/50 gearing. (Interestingly, on the YZ450Fs that Justin Seeds races in WORCS and NGPC, gearing is slightly taller at 13/49, though Woolsey observes, “It’s just the way the motor hits [in the MX-focused ’450F] so that’s why we dropped it down to the 49. The [YZ450FX] is really [interesting]; yeah, it got to a better top speed, but for time to speed, corner to corner, it was dramatically [increased]. It worked awesome in the valleys, but everywhere else, it lost time, like three or four bike lengths just because it takes you longer to get up to speed.”

RK’s EXW XW-ring chain and DDC sprockets (13/50) spin the 18-inch rear Dunlop MX52 that contains a Dunlop foam insert to prevent flats. Note too the BRP chain guide.
RK’s EXW XW-ring chain and DDC sprockets (13/50) spin the 18-inch rear Dunlop MX52 that contains a Dunlop foam insert to prevent flats. Note too the BRP chain guide.Mark Kariya

For tires, it’s Dunlop with the MX3S in front and MX52 in back, though for the GPs, it’s usually the MX3S front and rear. Naturally, all team riders run foam inserts to preclude the possibility of flats, with the Dunlop versions employed most of the time. As Woolsey shares, “To be honest, I kind of bounce back and forth. The guys [racing] NGPC, they like the Nitro Mousses and we haven’t had any issues with Nitro Mousse, but Nick and Axel at the beginning of the year did not like the feel of them, so we stick with Dunlops in the desert.”

To ward off the inevitable abuse that desert racing throws at machine (as well as at man), the Purvines group installs a number of Bullet Proof Designs guards: chain guide, radiator, and rear-brake rotor sharkfin. AXP Racing, however, provides the polymer skid plate with a few Works Connection guards and bling also found throughout.

Above the triple clamps, the team relies exclusively on Fasst Company’s Flexx handlebars, the 12-degree bend the universal team choice along with the red elastomer “bumpers.” A’ME’s full-waffle grips as well as ARC levers/perches are preferred by both Burson and Lynn, and GPR’s V4d steering stabilizer helps tame unexpected deflection.

The team uses Seat Concepts products, though Woolsey points out, “Neither one’s real particular on foam. Seat Concepts has been awesome because they’ve been sending me complete seat assemblies [when I build the bikes] for the past year or so, although their covers go on super, super easy. But usually it’s just stock foam or whatever their stock replacement foam is, [even keeping the height the same as stock]. Neither one of them is really very picky on that—they don’t spend enough time sitting down to worry about it.”

As for the IMS tank, Burson uses the 2.4-gallon version for his 2018 ’FX, though on the team’s 2019 YZ450Fs for GPs, the 2.9-gallon tank is utilized. “There’s some modification required because I have to use the ’FX fuel pump and ’FX wiring for the fuel pump because it is different,” Woolsey notes. “But for [the added capacity], it’s worth it.”

Finally, there’s the RAD Custom Graphics kit that provides the aesthetic upgrade.