THE MOST EXTENSIVE 2021 125cc SHOOTOUT YOU WILL EVER WATCH
TWO-STROKE SPOTLIGHT: BOB PATCHETT’S 1976 SUZUKI RM125
-Race Tech fork rebuild
-Noleen Marty Tripe vintage shocks.
-Buchanan black anodized rims and heavy stainless spokes.
-Full sandblast and powder coat of all components. Every nut-bolt new OEM.
-Vintage Suzuki plastics and PPG paint to redo tank to match plastics.
-Super fun and fast bike
Editors Note: Please keep those submissions coming. If you would like your bike to be featured in the “Two-Stroke Spotlight,” please email me at firstname.lastname@example.org. All I ask is that you give a breakdown of your bike and a detailed description of the build. Please also send a few photos of your steed. By submitting your bike for the “Two-Stroke Spotlight,” you agree to release all ownership rights to the images and copy to MXA.
ALL THE 2022 450 BIKES THUS FAR
MXA YOUTUBE CHANNEL | HIT THAT SUBSCRIBE BUTTON
BRUTAL SAND TRAINING! WITH FAST FREDDIE NOREN
ANCIENT ART OF FUEL-SCREW KNOW-HOW
I own a 2013 Yamaha YZ250F. It is a good bike, but its real claim to fame is that it was the last carbureted 250cc four-stroke. I have some jetting issues, and a guy said that there is something called a fuel screw on the carb that will allow me to make the bike richer or leaner. Where is it, and how do I adjust it?
The fuel screw bleeds down how much fuel mixes with the air coming from the carb’s bypass hole. Do not mistake it for a two-stroke’s air screw. The air screw is on the side of the carburetor and meters the amount of air that makes it to the pilot-jet nozzle. A fuel screw is located underneath the float bowl and meters the amount of fuel that makes it to the carb’s main body. Four-strokes use fuel screws instead of air screws because they don’t have enough low-speed vacuum for an air screw. At low rpm, a four-stroke creates less engine vacuum than a two-stroke. It is the vacuum created by the engine that sucks fuel out of the float bowl and into the engine. Thanks to the fuel screw, a four-stroke is able to start easier and run cleanly at its very low-rpm idle speed by getting fuel via the fuel screw.
Before you touch the fuel-mixture screw, you must first warm up the engine and then bring it to a fast idle. As a rule of thumb, 1800 rpm will do. With the engine at a steady idle, turn the fuel screw in, which lessens the amount of fuel. Continue tightening the screw until the engine rpm drops (and nearly dies). Now, slowly turn the screw back out, which increases the amount of fuel. You will hear the engine rpm begin to speed up and the exhaust note will become crisper.
Stop turning the fuel-mixture screw at the exact moment when the engine hits peak rpm. Peak rpm is when the engine runs the cleanest and fastest. If you keep turning the screw out, the rpm will stay up but the exhaust note will become dull, flat and lumpy. If you have any doubts about the best setting, turn the fuel screw back in until the rpm slows down, and turn it back out again until it speeds up.
There is no right number of turns, only wrong numbers. Typically, the fuel screw can be set anywhere from 1/2 to two turns out. If you have to turn it more than two turns out before it reaches peak rpm, it might indicate that the pilot jet is too small (lean). Try the next larger pilot and retest the fuel-mixture adjustment. Conversely, if peak rpm is reached before you turn the fuel-mixture screw out a half turn, it could mean that the pilot jet is too rich. Try the next smaller size.
Sadly, you will need to check your fuel screw any time the temperature changes—twice a day if it is cool and overcast during practice, and bright and sunny for the first moto. Changes in temperature, elevation and humidity will require fuel-screw adjustments. To avoid having to squeeze a tiny screwdriver up under the Keihin carb, you can buy an aftermarket fuel screw that sticks below the float bowl and can be turned by hand.
Accidents on the track can happen like casing a jump or bumping into another rider. When
mishaps like this arise, it could result in a part on your bike either bending or breaking. Luckily for 2013-2021 CRF110F
riders, we here at Pro Circuit have just stocked a part that can offer additional support. Our Shift Shaft Brace is a
CNC-machined part that sits just behind the shift lever and offers added protection for the shift shaft to prevent it from
bending. Since the shift shaft sticks out on the 110, it’s always best to have more support and to protect the transmission
from serious damage. Don’t be left with a bent shift shaft and have to replace it, so pick up a Pro Circuit Shift Shaft Brace
for increased protection and a factory look.
Please note that the plastic countershaft sprocket cover will need some custom cutting for the shift shaft brace to
“THIS WEEK IN MXA” WITH JOSH MOSIMAN: THE FUTURE OF MOTOCROSS ON TV
WANNA RACE IN SOCAL? NEED TO RENT A BIKE? FIND A PLACE TO STAY? JUST CALL STAPO WHEN YOU CAN TRAVEL AGAIN
In his spare time, when he’s not testing with MXA, racing in a foreign country, going to Japan or helping many of his motocross buddies, MXA test rider Dennis Stapleton opens up his house, garage, bikes and mechanics to help riders who would like to come to SoCal on a motocross vacation—and now that the coronavirus pandemic is waning in the USA and the country is opening back up, foreign riders will be able to come to America to race, train and sightee again. You should plan ahead and make your reservations now for this upcoming Summer and Fall. Dennis offers full service to all of the Southern California tracks for racers or for play riders. Whether you want to rent a bike, move in for a week, race at Glen Helen or take motocross lessons—this is one-stop shopping. Just send them an email (Stapoknobbyshop@gmail.com). If you’d like to live the SoCal lifestyle for a day, a weekend, a week, a month or three months, visit Dennis Stapleton’s’ website at www.knobbyshopsouth.org for more details!
MOTO | TRIVIA
TAKE THE MXA SURVEY FOR A CHANCE TO WIN A SUNDAY MOTORS FLAT TRACKER
Don’t pass on this opportunity to win a free Sunday Motors bike! Completely fill out the annual “Reader Survey” below or click here. We’ll take your input to help improve both the web and monthly print content of Motocross Action. One lucky winner will be chosen at random to receive a bike from Sunday Motors. For a few minutes of your time, you’ll be entered into a drawing to win this Sunday Motors S 147 flat-track motorcycle. The S 147 model features a 150cc engine, Mikuni carburetor, 14-inch front/rear tire, stainless steel footpegs, bottom-mount brake caliper, YCF 310mm rear shock, 200mm rear disc, low-exhaust configuration system, and kill switch with leash. One winner will be chosen on July 6, 2021.
The MXA wrecking crew is busy year-round testing motorcycles and producing content for the magazine and website, but once a year we compile a “reader survey” to help us learn more about our loyal magazine/website readers and viewers. We take your input on the survey to help improve both the website and monthly print content coming from Motocross Action. This year, we are offering the super cool opportunity of winning a Sunday Motors 147 Flat Track motorcycle! Completely fill out the annual MXA Reader Survey by click here. One lucky winner will be chosen at random to receive a bike from Sunday Motors and you’ll be helping us out as we strive forward continuing to testing motorcycles, parts and gear. One winner will be chosen on July 6, 2021.
TALK MOTO WITH MOTO MINDED PEOPLE. JOIN MXA’S FACEBOOK GROUP CHAT
THE JULY 2021 ISSUE OF MXA IS HERE NOW? YOU DO SUBSCRIBE DON’T YOU? IT IS THE BEST DEAL IN THE SPORT
HOW TO SUBSCRIBE TO MXA SO THAT YOU NEVER MISS ANOTHER ISSUE, PLUS GET A $25 ROCKY MOUNTAIN GIFT CREDIT TO COVER YOUR COSTS
If you subscribe to MXA you can get the mag on your iPhone, iPad, Kindle or Android by going to the Apple Store, Amazon or Google Play or in a digital version. Even better you can subscribe to Motocross Action and get the awesome print edition delivered to your house by a uniformed employee of the U.S. Government. Did we mention the $25 gift card for any part you want from Rocky Mountain ATV/MX? You can call (800) 767-0345 or Click Here (or on the box at the bottom of this page) to subscribe.
Moto Trivia answer: Billy Payne 1999 on a Pro Circuit KX125.