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MARCH 29–YZF470

A Yamaha for the woods

In the last few issues, we’ve featured several Yamaha YFZ450s decked out and ready for the motocross track. From our project YFZ and Tavis Cain?s Duncan YFZ to Kory Ellis? Alba/GYTR race winner, these machines are track-ready rockets. Now, we have the first test of a true woods YFZ. Four Stroke Tech (FST) has been building big bore cross country racers for well over a decade now and if anyone could get more ponies out of the YFZ, it would be them.

The staff of FST got to work early on the new Yamaha as part of a support program for XC star Chad Duvall. At the end of last season, Duvall got the call to become a Yamaha factory rider and parted ways with FST. Sure, a factory ride is good for Duvall, but the chances of you buying the same YFZ parts Duvall uses are slim. On the upside, FST continued development on the YFZ and created a woods rocket that is smooth to control and has gobs of low-end power. Best of all, the parts are available to the general public.

To make the Yamaha YFZ do well in the woods it needs lower gear ratios, more bottom end and plusher suspension. Stock, the YFZ is built for the MX track with a tall first gear (good for starts), high revving motor (for roost-throwing horsepower) and stiff suspension that?s good for pounding the whoops or the occasional flat landing.

MAKING A MONSTER
The main objective in turning any quad into a woods racer is finding bottom-end horsepower. That means you want the machine to pull hard without having to rev the motor very high. This allows for fewer shifts and a less demanding ride.

On the YFZ450, FST accomplished this with a typical big bore piston. On the YFZ450 there is no room to stroke the motor (change the rod size) so a 30cc larger 98mm Wiseco 12:1 piston kit ($205) was used. To make it fit, FST has to bore and re-Nikasil the cylinder ($195). FST offers a cam ($160) that gives the YFZ more top end but opted not to use one for this project. Instead they port and flowed the head (cleaned up) for an additional $250.

To allow this monster engine to breath, FST found the Pingry high flow air box and the exotic White Brothers stepped head pipe with carbon fiber muffler $750) worked the best. The carburetor was left stock except for the addition of a WR450 needle and a 190 main jet. As always when you add this much horsepower (approx. 60hp) to an engine, you?ll want to make sure every bit of it makes it to the ground, so FST installs their own heavy duty clutch springs ($20) along with a complete Hinson clutch. To help cool this monster, a Pingry?s +1 quart oil tank was utilized. The radiator remained stock.

THE SKELETON
To have the best engine of the bunch is one thing, but to win races you need the best chassis as well. Since this creation was made to run in the Pro Production class, the frame remained stock except for a fresh powder coating. However, the rolling chassis is about as far from stock as you can get. Houser (740-528-4111) supplied the plus one inch A-arms and a stock length swing arm and plus three steering stem. Houser has swingarms that will accept the stock bearing carrier or a Honda round type. Shock absorbers were supplied by Elka for this project. As a matter of fact FST has been a part of Elka?s XC development program for some time and is one of the reasons their shocks are as good as they are today.

Dura Blue supplied the rear axle and hubs while Hard Core hubs were used up front. FST changed to a Honda bolt pattern so sharing spare tires at the races would be easier. Speaking of tires, Maxxis Razr 2?s mounted on Douglas wheels are used on all of FST team quads. AC Racing took care of the bumpers and footpegs. However, FST lowered the pegs an inch and a half.

To keep things safe under the machine, Badger (859-760-2822) covered the underbelly and the swingarm with their stainless steel skid plates. Rider protection is provided by Cycra hand guards mounted on Renthal bars. Finally, to help slow this monster down, FST removed the stock rubber brake lines and installed a set of White Brothers steel braided lines.

THE RIDE
We hooked up with the FST crew at a recent round of the ATVA cross country series and took their fine tuned YFZ for a spin. The first thing we notice is how comfortable this Yamaha was. Compared to a stocker, that has you hunched over to control it, on this machine a more upwards seating position was obtained. The taller steering stem, high CR bend Renthal bars and lowered foot pegs all contributed to the improved comfort. FST replaced the stock battery with one out of a drag racing street bike to help start the new 12:1 motor quickly. In cross country racing, the start is crucial.

Out on the track this quad had tons of low-end power. With low revs we could zig-zag in and out of the trees with ease. Gear selection became unimportant on this ride. You could carry a gear or even two out of the tightest corners. The power would build strong and very smooth. We were pleasantly surprised that the motor lost its tendency to stall if you?re not hard on the gas out of a turn. This makes it nice for chugging through the mud or up a steep slippery hill.

Even if you?re not into the cross country racing scene, this motor kit can help you explore the tighter trails with less effort. The very smooth linear power along with the Houser steering stem reduce the YFZ vibration to undetectable levels.

Handling on the FST quad was far superior to anything we have ridden in the woods. The quad stayed low and flat around every corner with only the slight hint of roll in the corners. Having lower footpegs help us hold on during high-speed sharp turns.

The suspension soaked up the bumps like they weren?t even there. Tree roots, ruts and holes felt much smaller the harder you hit them.

Four Stroke Tech didn?t make the YFZ much faster; they made it easier to go faster on. Sure, everyone can go fast in a straight line; with this machine you?ll have more fun connecting hundreds of short straight lines. Throw in a few bumps and you?ll have the time of your life on a machine like this. FST can build you a woods racer or just a forest cruiser; it?s your choice. Call them at (814) 842-6159.

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