MXA LOG BOOK: SECRETS OF THE 2017 YAMAHA YZ450F

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No bike is perfect when it rolls off the showroom floor, and that is as true for the Yamaha YZ450F as for the KTM 450SXF, Kawasaki KX450F, Suzuki RM-Z450, Husky FC450 or Honda CRF450; however, the 2017 YZ450F finished way back in the “2017 MXA 450 Shootout.” So, if you want your YZ450F to be better, faster and sleeker, you won’t get there by riding it stock. What follows is a chronicle of the changes that can be made to any 2017 Yamaha YZ450F, but, most significant, we made them to Jon Ortner’s personal Simi Valley Cycles-sponsored YZ450F. We offer this as a racer’s guide to the 2017 Yamaha YZ450F.

YZ450F AIRBOX ISSUES

Twin Air’s Power Flow kit is outfitted with an oversized, flame-retardant air filter and CNC-machined aluminum cage.

The airbox on the new-generation 2017 Yamaha YZ450F should be in the Engineering Hall of Shame. It takes a safe-cracker to get into, and once you have opened the vault, the stock filter isn’t much to look at. MXA found solace in the newest Twin Air PowerFlow kit. It isn’t just a new air filter but a totally new airbox, intake tract, cage and cover. It almost doubles the size of the filter and the available air in the airbox. The hump-back airbox looks odd, but it makes a noticeable improvement to throttle response and over-rev. For more information, go to www.twinair.com or call (800) 749-2890.

HEAVIER FLYWHEEL WEIGHT FOR BETTER HANDLING

This might sound strange, but one of the best-handling mods that we made to the 2017 YZ450F was to put a Steahly 9-ounce flywheel weight on it. In stock trim, the YZ450F is aggressive at first crack of the throttle, which leads to unwanted wheelspin in slick or slippery situations and, conversely, jumpiness in tacky situations. Deep sand and fast pros may prefer that hit, but most MXA test riders wanted more throttle control and broader power. After racing with and without the Steahly-modified flywheel, every test rider was generous in his praise of the benefits of the heavier flywheel. The goal was to make the YZ450F feel torquey, smooth out the powerband and focus on manageable power.

The Steahly YZ450F flywheel weight isn’t a bolt-on project (as it requires gluing and baking), but Steahly will do the hard work for you for a small surcharge. For more information, go to www.steahlyoffroad.com.

CLUTCH-PLATE ROULETTE

Of all of the production Japanese clutches, the Yamaha’s is the best. It lasts longer and feels better than anything that Honda, Suzuki or Kawasaki have to offer. The cheapest way to improve the YZ450F clutch is to understand that the eight-plate clutch pack has two different types of clutch plates—grippy and standard. In stock trim, the clutch has three grippy clutch plates (part number 5VP-16321-00) and five standard clutch plates (part number 5PA-16321-00). If you want a stronger clutch, replace some of the standard plates with grippy plates. You can replace all five or just two or three to modulate the feel. One caveat: the standard plates should be used in the innermost and outermost positions in the clutch stack. That said, the YZ450F is still not up to the standards set by KTM. To help the clutch survive, we added stiffer Pro Circuit clutch springs. For our AMA Pro test riders, we went with a complete Hinson clutch.

ADJUSTABLE JGR SHOCK LINKAGE

The YZ450F is a bike with a strange mix of handling sensations—some of them caused by the stinkbug stance. Our fix was to install adjustable JGRMX shock-link arms. JGR links can be set from 142mm to 146mm long (when the JGR team raced YZ450Fs, they ran the links at 144mm). The longer links lowered the rear end from 8mm to 14mm to 19mm to 23mm, depending on where we set it. This allowed us to lower the overall frame height by sliding the forks up in the clamps. Plus, with a lower rear end, we had more range in changing the head angle with fork-height settings. The 2018 Yamaha YZ450F’s seat hieght is 20mm lower.

COOL RUNNINGS

For summer racing, we wanted our YZ450F to run cooler. We believe that Cycra’s PowerFlow plastic not only makes the YZ450F narrower but allows more air to reach the radiators. Unfortunately for us, the Cycra radiator shrouds wouldn’t work with our humpback Twin Air Power Flow airbox cover. So, we added a Boyesen Supercooler water-pump cover and impeller. The Boyesen pump eliminates cavitation, which means more water and fewer air bubbles in the cooling system. As has become rote, we drop-kicked the 1.1 kg/cm² radiator cap (15.6 psi) for a higher-pressure 2.0 kg/cm² cap (25.6 psi) from CV4 Products to raise the boiling point of the antifreeze from 265 degrees Fahrenheit to 278 degrees.

CYCRA POWERFLOW PLASTIC

Yamaha’s 2018 production plastic is based the Cycra PowerFlow YZ450F plastic. The Cycra PowerFlow radiator wings eliminate all of Yamaha’s duct work and double-wall plumbing to produce a sleeker, narrower and cleaner tank/radiator interface. It is a clean design and can be ordered with just the radiator wings and airbox cover or as a complete plastics kit. We could not mate the Cycra radiator wings to our humpbacked Twin Air airbox, but if we could, we would.

HOPPED UP ON STEROIDS

We tested Pro Circuit, DR.D and FMF exhaust pipes, and they all upped the oomph, especially when combined with better breathing, crisper mapping and dialed-in geometry. As a rule of thumb, fuel-injected bikes thrive on aftermarket exhaust systems. They tend to increase over-rev while taming the barky throttle response off-idle. Surprisingly, there is a percentage of MXA test riders who prefer to run slip-on muffler systems instead of full systems, and another group who like the mellow power delivery of the stock YZ450F system.

MAP IT FOR BETTER POWER

We love Yamaha’s GYTR Power Tuner. It doesn’t produce more horsepower, but it allows the rider to advance and retard the ignition to produce different styles of power. Note that you need different maps for bikes with the mellow stock exhaust and better-breathing aftermarket pipes.

For the stock pipe, we ran close to the stock fuel map with a little more fuel on top. As for the ignition mapping, we advanced it in every box, save for the high-rpm wide-open box where we retard it 3 degrees.

For aftermarket pipes, we leaned out the fuel mixture in four of the nine boxes (the other five we left alone). As for the ignition mapping, we advanced it by 1 degree at small and middle throttle openings. The Power Tuner will not work on the 2018 Yamaha YZ450F as it has switched to wi-fi.

FIXING THE POP-OFF SPARK-PLUG CAP

If this hadn’t happened to us, and we hadn’t discovered that it happened to the factory Yamaha teams, too (including JGR and Star Yamaha), we wouldn’t believe it. The YZ-F spark-plug cap is totally sealed where it enters the valve cover. Trapped water bleeds out through a hole cast in the side of the cylinder head. But, if this hole gets clogged, the heat of the engine will cause a rapid rise in air pressure in the sealed spark-plug chamber. This pressure can actually pop the spark plug cap off of the spark plug. The first sign that you have spark-plug-cap issues is if the bike starts to run ratty on the top end. If you have doubts, reach under the gas tank and push down on the spark-plug cap. If it snaps back on the plug lead, you have identified the problem. We ran a JGRMX Yamaha spark plug cap holder. It mounts to the valve-cover bolts and holds the spark plug cap down. Of course, keeping the bleed hole clean is also required. The 2018 Yamha YZ450F has an almost identical spark plug cap holder stock.

GEARING FOR THE MASSES

Every MXA test rider complained that the bike would fall off the pipe on the second-to-third shift in heavy loam, sand or going up hills. We wanted to race the YZ450F in the broader third gear to avoid having to rev it in second gear. The fix? Gear it down. We ran 13/49. The stock rear sprocket is a 48.

LAUNCH CONTROL

Suzuki, KTM, Kawasaki and Husqvarna all have the same basic launch control systems (Honda doesn’t have launch control). The typical launch control system retards the ignition dramatically from 7000 rpm on up (because you aren’t going to launch off the starting line below 7000 rpm). This knocks off 3 to 5 horsepower to help the rear tire bite instead of spin. These systems stay engaged until you shift up, chop the throttle or run out the timer clock. Yamaha’s launch control system is different. How so? From 4500 rpm and 30-percent throttle openings, Yamaha’s launch control system reduces horsepower much more than the competing systems. Less horsepower translates into less wheel spin and more forward hookup. Once the YZ450F clears the starting gate and travels between 30 and 60 feet off the line, the horsepower ramps back up to max power without you doing a thing. Yamaha’s Launch Control System (LCS) restores full power once the rpm, throttle position sensors and gear selector match a logarithm that tells the ECU that the bike is no longer in roll-on power mode. If you never get the dots and dashes into the required box—the LCS will automatically turn itself off when you shift to third.

TRIPLE CLAMP OFFSET

Yamaha changed the triple clamp offset from 22mm to 25mm in 2016. This may seem like an earth-shattering move on the geometry front, but, in reality, it is just a return to the previous 2009 offset. But, curiosity made us want to go back to the 22mm offset that Yamaha originally switched to in 2010. We ordered Pro Circuit’s 22mm triple clamps and liked the way the YZ450F felt on the entrance of turns. It wasn’t a slam-dunk change, but in conjunction with the longer JGR shock linkage, it made us as happy as we’ve been with the YZ450F’s ability to track through corners without that irritating wiggle. For more information, go to www.procircuit.com. Guess what? The 2018 Yamaha YZ450F has 22mm offset again.

GET A HANDLE ON THE YZ450F

You might be surprised to learn that most of our engine changes (mapping, flywheel weight and gearing) were made in the name of handling more than horses. But, we did make a lot of other chassis changes. Here’s the list:

(1) Fork height. We slid the forks up in the clamps to steepen the head angle and to put more weight on the front wheel. This lessens the looseness at the entrance to turns, but it requires trial and error to avoid oversteer. If you run a longer link, you will need to slide the forks up in the clamps to maintain chassis balance

(2) Race sag. We lowered the rear sag from 100mm to 103mm in conjunction with sliding the forks up. This got rid of the YZ450F’s inherent stinkbug seat height.

(3) Shock linkage. A longer shock linkage helped even more with chassis balance and worked well with the slightly softer shock spring that the engineers added in 2016.

(4) High-speed adjuster. Most of our rear shock adjustments were made with the high-speed compression adjuster. We tended to turn it out to help the rear settle more under a load.

(5) Front tire. Always run the best front tire possible on the awkward-turning YZ450F. Cheap rubber is a recipe for disaster.

We aren’t YZ450F defenders. We know better than most that the YZ450F can be awkward-feeling on the entrance to flat or sweeping turns. We have been critical of Yamaha’s front-end response for as long as we can remember. Superb handling has never been a Yamaha strong point—suspension, yes; cornering, no. A contributing factor to the YZ450F’s ungainly feel is its weird ergonomics. In stock trim, it feels too tall in the rear. It gives the impression that it’s overly wide at the radiators. It feels tippy and top-heavy. It isn’t flat enough for our tastes. And, creative centralization of mass can’t make up for the 238 pounds.

DO-IT-YOURSELF FRAME KITS

Many riders try to retro-fix the feel of the YZ450F by moving the engine forward by 1.5mm to put more weight on the front wheel, which essentially brings the weight bias back to where it was on pre-2010 YZ450Fs. Prior to the latest 2015–2017 YZ450F, DR.D offered engine relocation kits that moved the YZ450F engine forward 2.5mm. The 2016–2017 DR.D kit relocates the engine 1.5mm forward by using special eccentric swingarm pivot-bolt spacers. Additionally, DR.D offers a kit that lowers the radiators by 27mm in an attempt to bring the water weight down on the frame.

THAT SPECIAL LOOK

The MXA wrecking crew loves the guys at Decal Works. They save our bacon all the time. Every time we set out to build a project bike, we procrastinate on the color of the plastic, sponsor logos and overall look of the bike. Sometimes we start with the stock plastic and then switch to Cycra, which means that all-new graphics have to be built at Decal Works. They never complain when we say that we have to have it by tomorrow or when we change our minds about the color. And, most important, when we need design help to pull the look of the bike together, they get it done for us. For our Simi Valley Cycle YZ450F, we gave Nick at Decal Works all the sponsor logos and told him to put them together. We think it looks great. For more information, go to www.decalmx.com or call (815) 784-4000.

MISSING RUBBER GROMMETS & DZUS FASTENERS

The rubber grommets on the upper half of the airbox, radiator ductwork and where the flip-top part of the seat plug in are prone to falling out. We also lose the the Dzus fasteners that hold the radiator shrouds. It is best to carry spare grommet and Dzus fasteners in your toolbox. Be aware that there are two different types of ductwork grommets. The radiator grommets part number is 90480-01558, while the seat grommets are 1SL-24742-00.

FREE-WHEELING FOR UNDER $600

We wanted a second set of wheels so that we could have different compound tires ready in an instant. Since the stock YZ450F wheels are adequate for the average racer (although our test riders had no intention of racing Supercross with them), we opted to go with Tusk Impact wheelsets (equipped with Tusk Typhoon brake rotors) for our backup wheels. The MXA wrecking crew has had great luck with Tusk wheels over the years. They are durable enough for regular use, stay true and we’ve never suffered a failure. Best of all, both wheels (with white hubs, black spokes and black rims) only cost $590. If you are buying the Tusk wheels to use as spares at the races, be sure to factor in the cost of new rotors (and rotor bolts); otherwise, you will have to change rotors every time you change wheels. The front and rear Tusk Typhoon rotors were only $120 ($130 with rotor bolts).

RELIABILITY: IT’S SPELLED Y-A-M-A-H-A

The reliability of the YZ450F engine is legendary.

If you are looking for the most reliable 450cc motocross bike made, look no further than the YZ450F. It is bulletproof. It never needs valve adjustment. Piston life is close to 100 hours, and nothing breaks on this bike. If you are a bike breaker, the Yamaha YZ450F is the best bike to own.

COOL STUFF THAT GRINDS ITSELF AWAY

Every rider has personal touches. MXA’s test YZ450F has the optional GYTR tall seat because the test rider is tall.

We feared that the water pump might be exposed to damage and installed a Cycra full-coverage skid plate to protect it. It’s made out of plastic and can take a lot of abuse. When we saw how banged up it was, we were glad that it took the hits instead of the bottom of the YZ450F. We ran miscellaneous JGRMX carbon fiber and anodized aluminum bits—chain guide, pipe heat shields, spark plug holder and axle blocks. We added a hard-anodized Pro Circuit clutch cover to make people think that we spent more money behind the cover than we actually did.

THE WEIGHT IS OVER

Once in motion the feeling of the weight does not go away.

Sorry, Charlie, but it would take cubic dollars to whittle significant weight off the 238-pound Yamaha YZ450F. It is 6 pounds heavier than a Honda CRF450, 8 pounds more than a Kawasaki KX450F, and 16 pounds above and beyond a KTM 450SXF. Spending thousands of dollars on titanium, air forks and carbon fiber might get it down to the weight of the Honda, but it will never come close to being light. We learned to embrace its tonnage, girth and height. It’s a big bike that’s best suited to big boys. We hate to break it to you, but the 2018 Yamaha YZ450F actually gained one pound and weighs 239 pounds (without fuel in the tank)—blame it on electric start.

FORK IT OVER

The suspension mods were handled by TBT Racing.

Yamaha has the best showroom stock suspension sold. The Kayaba SSS suspension is so good that the MXA test riders had no major complaints. In most cases, the YZ450F forks can be used without aftermarket springs or valving. Excellent forks. Below are the settings we ran on the stock Kayaba forks, but, paradoxically, we sent our YZ450F suspension to TBT Racing to have it re-valved. This customization made the forks much better, plusher and more resistant to bottoming. Most of all, the TBT valving kept the forks high in their stroke so they maintained considerable travel for upcoming bumps. For more information, contact TBT at (951) 707-7837 or www.tbtracing.com.

For hardcore racing, these are MXA’s recommended 2017 Yamaha YZ450F fork settings (stock settings are in parentheses).
Spring rate: 0.50 N/m
Oil quantity: 315cc
Compression: 10 clicks out (8 clicks out)
Rebound: 8 clicks out (10 clicks out)
Fork-leg height: 4mm up
Notes: For 2017, Yamaha has refined what were already the best forks on the market. What’s best about them? They work for Beginners, Novices and AMA Pros. They don’t care if you’re thin or fat, tall or short. There’s a setting for everyone. It is important that you get the chassis level by adjusting sag and fork height, though, so that neither end is overloaded.

SHOCK IT TO ME

For hardcore racing, these are MXA’s recommended 2017 YZ450F shock settings (stock settings are in parentheses).

Spring rate: 56 N/m
Race sag: 103mm (100mm stock)
Hi-compression: 2 turns out (1-1/2 turns out)
Lo-compression: 12 clicks out
Rebound: 9 clicks out (14 clicks out)
Notes: We ran an adjustable JGR shock linkage (not solely for suspension purposes, but also to give us more adjustment room with the head angle and frame geometry). The longer link drops the rear of the bike from the stock height to as much as 23mm and stiffens the initial part of the stroke. We compensate for the increase low-speed by turning the high-speed compression out a half turn and the rebound in five clicks. Additionally, we had TBT re-valve the YZ450F shock to match the rider’s weight, speed and favorite track.