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MXperts

HAVE YOU SEEN THE NEW MXA? YOU DON’T KNOW WHAT YOU ARE MISSING ? ON THE NEWSTANDS NOW!

Read those headlines again! Believe it or not KTM gained 5 horsepower in one year, while Kawasaki slowed down the KX450F and sped up the KX250F…and made both bikes better at the same time. This is the KTM 350SXF the way it should have been built back in 2011. If this bike had come out two years ago, there would be more racers on 350s today. Jody may be writing about modern motocross racers, but he went back to his younger days to make the point. This photo was shot at Saddleback Park 30 years ago. Tal…

ASK THE MXPERTS: WHY DOES MY 2006 YAMAHA YZ450F BOG AND DIE, BUT RUN A FEW MINUTES LATER?

Dear MXA,     My 2006 Yamaha YZ450F bogs and dies when I?m riding it. If I pull over and wait a few minutes it will run fine. Then the problem starts up again. What is wrong? The 2007 YZ450F got the four-bolt stator?not the 2006 model.     The 2006 Yamaha YZ450F had a three-bolt stator plate. It was prone to cracking, which would cause erratic running. In 2009 Yamaha fixed this by switching to a four-bolt stator plate. Unfortunately, you?ll have to buy a new three-bolt plat…

ASK THE MXPERTS: WHAT WOULD IT TAKE FOR KTM TO GET RYAN DUNGEY?

Only Ryan Dungey knows what he is going to do for 2012. Dear MXA,     Everyone has heard the rumors that Ryan Dungey will leave Team Suzuki for greener pastures in 2012, but is there any truth to the rumor that he will move to Team KTM to be with Roger DeCoster?      First and foremost, we are officially in the silly season?thus any farfetched idea is fair game. The DeCoster connection is what makes the Dungey to KTM rumor seem so plausible. And, it didn?t hurt when DeCoste…

ASK THE MXPERTS: WHY DOES WATER WEEP FROM UNDER MY WATER PUMP?

Dear MXA,    I have a 2006 YZ250. When I fired the bike I noticed coolant leaking in a very small amount from a small hole in the bottom of the water pump cover. It didn’t leak much but I could find no reference in the manual about this. It never did this before. The hole looks like a small bolt or something might have fallen out of it. What is this and can I ride the bike? Do not try to put a bolt in the hole and do not ride the bike. The small hole between the water pump and oil seal is a we…

ASK THE MXPERTS: WHY DOESN’T MXA HAVE MORE BYLINES ON ITS STORIES?

Dear MXA ,     I noticed, and have heard other people comment, that there are no bylines on the stories in MXA . Why is this? Are you afraid? That crafty John Minert pulled a fast one and put a byline on this travel story about riding the 2011 Husqvarna’s in Italy. First of all, there are bylines on all “first person” stories (race coverage, travel stories or historical tales). Take the last few issues of MXA for examples: We put bylines on Dennis Stapelton’s “MXA Goes GNCC Racing” story …

ASK THE MXPERTS: WHAT IS THE PROPER 2007 HONDA CRF150 JETTING?

Dear MXA,     I bought my kid a 2007 Honda CRF150 from my brother-in-law. The bike is totally stock and never been race (only ridden around the family farm). Unfortunately, my kid wants to race, but the bike pops and bangs so bad that I think it is going to blow up. Are there any jetting changes I can make? Yes. The stock CRF150 jetting is a 135 main, 40 pilot, NHNT needle and 68 leak jet. It is not very good. Try these jetting specs: 138 main (richer), 38 pilot (leaner), NMQS needle (lea…

ASK THE MXPERTS: WHAT IS THAT HIGH-PITCHED SQUEAL COMING FROM MY CRF450?

Dear MXA,       I recently purchased a used 2006 Honda CRF450. Before taking my first ride, it emitted a high-pitched squeal. When I restarted the bike, the noise was gone. But, on my next outing the noise returned. Any ideas on what the problem might be?   The high-pitched squeal is coming from your kickstarter idler gear. The problem is that the oil level in your engine is too low. The check hole on the 2006 CRF450 is in the wrong place. The CRF check hole leaves you about 200…

ASK THE MXPERTS; IS IT TRUE THAT PISTONS AREN’T ROUND?

Dear MXA,    Is it true that piston aren’t round? A kid in auto shop told me this, but I have looked at a lot of pistons and they all look round to me. Are they round? They aren’t even close to round. Pistons are egg shaped from front to back. This egg shape is called “camming” in piston speak. Camming is hard to measure because the sides of the skirts aren’t there, but if you could measure them, you would find that many pistons are as much as 0.010″ out of round. Camming helps resists rocking…

ASK THE MXPERTS: MY 2006 YZ250 HAS A PERSISTENT YZ250 PING; WHAT CAN I DO?

Dear MXA,     My 2006 Yamaha YZ250 has stock jetting, lower gearing and a Pro Circuit pipe, but it pings under a load. What is the solution? You have two simple solutions: (1) Add a small amount of race gas to your pump gas (which you must be running since your YZ250 is pinging). Don’t run 100 percent race gas, just add one gallon of VP Racing C12 to four gallons of pump gas. That should fix your pinging problems. (2) Even cheaper, you can change the stock N3EJ needle for N3EW (the N3EW n…

ASK THE MXPERTS: WHO MADE THE FIRST SUCCESSFUL ALUMINUM FRAME?

Dear MXA,     Who made the first successful aluminum frame? Was it Honda in 1997 or someone else? 1977 Hagon. Greeves aluminum down tube from the 1950s. Almost 60 years ago there was a motocross bike with an aluminum frame (at least one-half of the frame was aluminum). The 1953 Greeves used a cast aluminum head tube and down tube in their Villiers-powered motocross bikes. But, the first, all-aluminum, monocoque, motocross bike was the British-built Hagon that Vic Eastwood raced in 1977. I…

ASK THE MXPERTS: CAN MY HANDLEBARS BE DAMAGED BY TIE-DOWNS

Dear MXA,      Can my handlebars be damaged by my tie-downs?      Yes. If the metal hoop on your tie-downs scratch the outer surface of your aluminum handlebars it creates a hot spot in the aluminum grain structure. Even a small scratch can create a stress riser which will focus energy to that spot (which on an oversize, crossbarless, aluminum handlebars just happens to be at the point of most flex). This can germinate into a crack. It is best to use the kind of t…

250/450 AMA NATIONAL RESULTS: DUNGEY WINS AGAIN AT THE 13TH NATIONAL OF THE YEAR:

This may look like a victory whip, but it is actually Ryan Dungey twisting his bike to get a good look at Roger DeCoster driving away. The 13th and final AMA National of the 12-race 2010 AMA National Motocross Championships came to a conclusion today at Barber Motorsports Park in Alabama. A estimated crowd of 65,00 spectators jammed the imaginative racetrack (well, actually 15,000 fans made it into the track, but the traffic jam on the roads to the course contained 40,000 people who wanted to be there a…