A clean motorcycle is a happy motorcycle. While washing your bike you will notice problems when they are still easy to fix.

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A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It’s all in the jetting.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at its best.

It’s very important that you start with the pilot circuit. The reason is simple. The pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to rejet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don’t seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet.

Once you have determined (and installed it if it’s necessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it’s time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it’s time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn’t really any way to test the needle other than by feel, but it’s usually quite obvious when it’s right or wrong.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between “rich” and “lean”, you’ll begin to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won’t go into that here.

Keep in mind; even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, and screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer.

Carburetor Animation

RG3 Suspension: Riding with Marvin Musquin & Ken Roczen from Kyle Cowling on Vimeo.

RG3 Suspension: Riding with Marvin Musquin & Ken Roczen from Kyle Cowling on Vimeo.

Circuit of Americas

• AMA/FIM Supercross
• AMA National Motocross
• AMA Women’s Motocross
• FIM World Motocross
• FIM Women’s World MX
• Supercross Tickets
• TV Listings

10 Things You May Have Missed on DirtRider.com:

1. A Two-Stroke With FI | 2011 Ossa TR280i Riding Impression http://bit.ly/qzgc6n
2. A 4-stroke company goes 2-stroke http://bit.ly/qE4zU8
3. A look at Alpinestars 2011 Fall Gear http://bit.ly/p1iwbq
4. Shan Moore gives you the Weekly Dirt http://bit.ly/qA8GN3
5. Carson Brown runs a Athena Big Bore Kit on his KX65 http://bit.ly/r1P0K6
6. First Ride: 2012 KTM 450 SX-F http://bit.ly/pYutiZ
7. Cairoli Victory at Lommel MXGP http://bit.ly/piJPvi
8. Kurt Caselli talks about ISDE 2011 http://bit.ly/qf3XyX
9. Enduro X Takes X Games Gold http://bit.ly/pCgpcs
10. 2010 EnduroCross Wallpapers http://bit.ly/npLxli

Research has shown that polystyrene loses 2% per year in its effectiveness due to simple evaporation. So with basic mathematics, in 5 years, you’ve lost 10% of your protection, and in 10 year, you’ve lost 20%.

Read More…

and am unrelated bonus…

Fox MX: Photos from the 2011 AMA Motocross Championship Race – Round 2 Wortham, TX. http://fb.me/HkvuAbdY

All you have to do to be eligible for this is send in an email to matthespr@yahoo.com and that’s it! Every entry will be put into a draw and the lucky winner will be notified by email after the Las Vegas SX round.

Go ahead and get your name in for this cool prize and check out www.andrewshort.com!

More info…

Now on to the topic… Houston, Texas SX 2011.
Houston SX Pre-race report….

The 2011 XC bikes have a new frame and out of the box they have a limited  turning radius. The R&D guys at EE have found a quick fix for the limited turning radius of the new XC. The stock steering stops are adjusted out from the factory.

This limits the amount of movement of the handle bars. We feel that even if they are adjusted all the way in the steering is still too limited. The fix we are using is to replace the stock steering stop bolts with an 8×20 button head bolt.

We do not use a lock nut with the bolt we just bottom the bolt out and use thread locker.

This increases the turning radius and you still have proper triple clamp to radiator clearance. We hope this tip helps you enjoy that new bike even more.

More KTM Tech Tips here

The championship-winning Rockstar Makita Suzuki team and Roger DeCoster will be parting ways after the close of the 2010 Lucas Oil AMA Pro Motocross season.

DeCoster has been Team Manager for Suzuki’s Supercross and Motocross efforts for 15 years, and together they have earned numerous titles and championships. DeCoster will continue to lead the team through the final two rounds of the Motocross series.

With numerous titles under his guidance, long time Suzuki team manager Roger DeCoster leaves on the heels of handing Suzuki a Supercross and Motocross championship title.

The championship-winning Rockstar Makita Suzuki team, led by Ryan Dungey, earned the 2010 AMA/FIM Supercross title in May and wrapped up the 2010 Lucas Oil AMA Pro Motocross championship last weekend at Southwick, making him the most successful rookie in Supercross and Motocross history.

For now, the Rockstar Makita Suzuki team plans to focus on finishing off the 2010 season strong and celebrate the incredible year it has been. For 2011, the Rockstar Makita Suzuki team looks forward to defending its championships with Ryan Dungey sporting the number one plate in both the Supercross and Motocross series. The team will begin the search for a new manager in preparation for the 2011 race season.

American Suzuki Motor Corp., the Rockstar Makita Suzuki racing team, Rockstar Energy Drink, Makita Industrial Tools, Yoshimura R&D of America, and all the sponsors of the team wish Roger the best in his future endeavours and thank him for the great years spent together at the races.

“You can never replace an icon like Roger,” said Yoshimura R&D of America Vice President Don Sakakura. “However, with Suzuki and Yoshimura’s racing DNA still strong as ever, and with the core nucleus of the team staying the same, we are looking forward to defending the 2010′s championships. Roger has made great contributions with Suzuki and certainly has the utmost respect, friendship, and our acknowledgement of a job well done. We wish him nothing but good luck in the future.”