MOTOCROSS ACTION MID-WEEK REPORT

• Dylan Ferrandis gets win number 5 at Round 9. He still has a 39 point lead.
• Ferrandis goes 2-1 for his 5th win of the season.
• It was Yamaha’s first win at Budds Creek since 2015 when Justin Barcia won on a Yamaha.

• Ferrandis keeps his podium streak alive. He’s been on the podium all 9 rounds this season.
• Ferrandis became the first Frenchman to win Budds Creek in the 450 class.
• Roczen goes 1-2 for 2nd overall. It was his 5th podium of the season.
• Roczen now has 7 moto wins this season, 2 more than Ferrandis, but is still 2nd in the points.
• Tomac goes 4-3 for 3rd overall, his 5th podium of the season.
• Average finishes so far this season: Ferrandis 2.2, Roczen 5.1, Tomac 4.8

250 RECAP

• Jeremy Martin still fighting to catch up.
• Jeremy Martin goes 3-1 for the overall win. It was his 3rd win of the season, the most of all riders in the 250 class.

• It was Yamaha’s first 250MX win at Budds Creek since Stephane Roncada 2000.
• Martin now has 20 National wins. He is now tied with Steve Lamson for 4th place on the all-time 250MX win list.
• Jeremy Martin now has 6 moto wins, the most in the 250 class.

• Jett Lawrence goes 2-2 for 2nd. It was his 6th podium of the season. He gained 1 point on Justin Cooper.
• Justin Cooper goes 1-4 for 3rd overall. It was Cooper’s 9th podium of the season. Cooper’s points lead is down to 3 points.
• With Ferrandis winning the 450 and Martin winning the 250 it was a Yamaha sweep. The last time this happened was Round 7 in 2015 at RedBud when Jeremy Martin and Barcia pulled it off.
• Austin Forkner goes 4-5 for 5th overall, his best finish of the season.
• Average finish this season: J. Cooper 3.1, J. Lawrence, 3.2, J. Martin 5.8.

MXA TEAM TESTED: SLATER SKINS HIGH-FLOW YZ-F AIRBOX COVER

The MXA wrecking crew has never been big fans of the 2010 to 2021 Yamaha YZ airbox design. Last year MXA built a 60.83-horsepower YZ450F with nothing more than airbox mods. That was a 2.30-horsepower gain over the stock 2020 Yamaha’s 58.56 horsepower. What did we do to make such a major power improvement? We knew that the stock Yamaha air filter design didn’t flow very much air, so we combined a Twin Air Power Flow kit with a handmade airbox cover (from a left-over discontinued Twin Air part). It wasn’t attractive, but it made a lot of horsepower.

Two years ago, MXA built this YZ450F airbox cover out of discontinued plastic pieces combined with a Twin Air Power Flow kit to prove to Yamaha that their stock airbox design didn’t flow enough air. Yes, it was ugly, but what was beautiful was the 60.83-horsepower we got with no mods to the engine other than the airbox cover. 

We hoped that racers would follow in our footsteps, but our homemade humpback cover was a one-off, and there were no readily available high-volume airbox covers available at the time. Now, suddenly, there are several viable options from Nihilo, CRM, Lightspeed, VHM and Slater. It should be noted that all of these covers, save for Slater’s, are molded from carbon fiber and have prices as high as $360.00.

Not so with Slater Racing Products’ (SRP) YZ250F/YZ450F airbox cover. It is molded from plastic and retails for $80.00. You may remember John Slater from his sponsorship of the 2015–’16 Blue Buffalo team and from his many years of trying to popularize full bodywork on motocross bikes with Slater Skins. There is no need for expensive carbon fiber to replace a thin sheet of plastic—after all, plastic was good enough for the OEM Yamaha cover.

The more time the MXA wrecking crew spent with the stock Yamaha YZ450F air filter, the more we realized that the YZ450F air filter and airbox didn’t flow enough air to support an engine that can gulp 600 gallons of air a minute. We knew we needed more air. We have seen riders drill holes in the top of the YZ450F airbox cover to get more air into the airbox, but we didn’t want to do that because the turbulent combination of air coming in through the radiator wing vents and the air sucking through the drilled airbox cover holes could ruin the laminar flow air stream that produces horsepower. That’s not to say the holes wouldn’t introduce more air into the YZ450F,  just that it wouldn’t be optimum air. The YZ450F and YZ250F need a stable supply of air, and that is where the Slater High-Flow airbox cover comes into play. Not only is it larger, it has ram-air vents in the front of the cover.

A dyno cannot fully test the Slater High-Flow airbox cover’s possibilities. Why not? Because the motorcycle is static on a dyno. The only air coming into the airbox is coming from the cooling fans aimed at the radiators. But, MXA dynoed it anyway. It produced  1/2 horsepower more at low rpm and 1/2 horsepower more from mid on up. But, on the track, as expected, once the bike was moving, the quantity of air was greatly increased, and, on the seat-of-the-pants dyno, the Slater Skins airbox cover was worth more than a 1/2 horse on top and bottom. It made the throttle response crisper, revved quicker through the midrange and felt fuller under a load. The SRP airbox cover is available in black or white plastic, with optional graphic packages to make it blue or grey.

We had three quibbles. (1) As if the YZ250F and YZ450F weren’t loud enough already, the suction sound coming from the SRP airbox was a cacophony of irritating noises. Be forewarned that any vent that air can get through, dirt can get through also. (2) We wish that SRP had been willing to go bigger on the air volume, because we know from experience that more air is always better. (3) The wire screen in the vents looked like it wasn’t mounted strongly, but we never broke it out during testing and we have been using the Slater airbox cover for six months now.

DIGITS? $80.00— www.srpinternational.com or (203) 878-2379.

MXA RATING: A nice, tidy improvement for 2018 to 2021 YZ450Fs and 2019 to 2021 YZ250Fs.

MXA PHOTO OF THE WEEK: FROM 38 YEARS AGO

MXA has been testing motocross bikes since 1973. This 1983 MXA 250 Shootout photo was memorable not just because of its unique set-up, but because the four MXA test riders from 34 years ago were (from top to bottom) Gary Jones, Jody Weisel, David Gerig and Lance Moorewood. Photo: Ketchup Cox

THE SEPTEMBER 2021 ISSUE OF MXA IS OUT NOW? SUBSCRIBE! IT IS THE BEST DEAL IN THE SPORT!

The September 2021 issue of MXA is awesome. Not only did we build a GasGas MC 450F Factory Edition—with the sole goal of not using a boatload of Power Parts accessories, we also built a 44-horsepower KTM 150SX. Well, actually, we had Mitch Payton build the engine for us, but we took it to the World Two-Stroke Championship and holeshot both 125 Pro motos (yes, 150s are legal in the 125 class at the World Two-Stroke Championship). Then, we tested a 2022 TM 112MX SuperMini, while revealing photos of the 2022 Kawasaki KX112 SuperMini a few pages earlier. We interviewed Jammin’ Jimmy Weinert, had Mitch Payton explain the hoops that Pro Circuit had to jump through to stay afloat during the Covid-19 pandemic and, as the ultimate kicker, we had Josh Mosiman join the U.S. Air Force so we could get our hands on an F-16 Fighting Falcon for a test ride—see the photo below of Josh and his two favorite machines.

CHECK OUT THIS TRICK 2003 KAWASAKI KX144

BIKES YOU’VE NEVER SEEN BEFORE: 1965 JAWA 250 BANANA FRAME

The most distinctive feature of the 1965 Jawa was its unique hanger frame.

Jawa is a motorcycle manufacturer founded in Prague, Czechoslovakia in 1929 by Frantisek Janecek, who originally bought the motorcycle division of Wanderer.  When he started his own brand, he named it “Jawa” which was made up of the first two letters of Janecek and Wanderer.

Most American motocrossers know little or nothing about Jawa, least of all about the Jawa banana frame. The banana frame was one of the most iconic motocross bikes of the mid-1960s. Jawa and CZ were joined at the hip by their communist commisaars, but Jawa was the better of the two (until management told them to focused on offroad events instead of motocross).

The radical Jawa banana frame was designed and developed by chief Jawa engineer Jan Krivka in 1963. The bike featured a cassette gearbox which could be slid out the right side with the engine still in the frame. Likewise the crankshaft could be removed from the left side. The engine had a single exhaust port which emptied into two expansion chambers.

The banana frame Jawa  featured a magnesium engine, one-into-two expansion chamber, Girling shocks, CZ forks, steel gas tank and a 246cc engine fueled by a 32mm Jikov carb.

It was never officially called the “Banana Frame,” but that is the nickname that stuck to it because of the engine hung below two curved tubes that extended from the steering  head to the rear shock mounts. To casual viewers they were curved like a banana.

Vlastimil Valek was sixth in the 1965 FIM 250 World Championships on the Banana Frame and a year later raced a 400cc version to fourth in the 500 World Championships. The Banana Frame was replaced with a conventional frame in 1967.

1963 Jawa released the type 579, which was the actual Jawa model name. They came in 250cc and 350cc two-stroke version. They where lighter and faster than the type 557 they replaced. In 1964, 1965 and 1966 Jawa struggled with the Banana Frame production bike. Vlastimil Valek and Peter Dobry raced the bikes and Valek kept the brand near the front in the 250 GPs.

The last of the Banana Frames was the 1966 Jawa 402.

The last season of the “Banana Frame” was 1966 when bike Valek raced a Jawa 402cc in the 1966 500 GPs managing to take sixth place in the final standings. Jawa switched to a dual down tube conventional frame design for 1967. Photos by Justyn Norek.

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