2009 Yamaha YZ125 Two-Stroke; Suspension Settings, Jetting Specs, Likes & Dislikes, Plus Much More

On Feb 26, 2009 Last updated Feb 14, 2018

MXA RACE TEST: THE NEW 2009 YZ125
MAY WELL BE THE LAST OF ITS KIND & THE BEST OF ITS KIND

Have you ever heard the phrase, “Hoisted by their own petard?” Nothing better defines the 2009 Yamaha YZ125 than that archaic phrase. Why? And what does it mean? A petard was a military weapon that was used to blow holes in the walls of fortresses. The metallic device was filled with gun powder and used much in the same way as the modern “shaped charge” to direct force in the desired direction. It was an awesome weapon by 16th century warfare standards, but every now and then a petard would explode unexpectedly, blowing its handlers into the air-?thus they were “hoisted by their own petard.”

And so it is with the 2009 Yamaha YZ125. It too is a brilliant weapon of warfare, and since 1996 the YZ125 has owned the 125cc class, lock, stock and barrel. Then Yamaha, flush with the success of the YZ400 four-stroke, decided to build the 2001 Yamaha YZ250F four-stroke. It was the 2001 equivalent of the 16th century petard. It was an explosive new machine that was going to blow holes in all the other competitors in the 125 class. It did. But in the process, the YZ250F not only drove every other manufacturer out of the 125 two-stroke business (and into the four-stroke fold), but it killed sales for the very popular YZ125. Today, YZ125 sales are one-half of what they were in 2005. Thus, the YZ250F blew up the YZ125 and left Yamaha hoisted by their own petard.

There is no doubt that the YZ125 has been maimed by the 250cc four-stroke explosion (which reached every manufacturer by 2004). YZ125 sales have dipped to the point where it may not be profitable for Yamaha to keep producing them. Yamaha’s only competitor for 125cc two-stroke sales, KTM, abandoned the 125cc formula by selling twice as many bored-out KTM 144SX and 150SX models as 125SX’s. The fuse has been lit for the venerable small-bore two-stroke. It will explode in the near future.

Q: WHY SHOULD WE MOURN THE DEATH OF THE 125 TWO-STROKE?

A: There are many reasons, but here are three good ones:

(1) Price. With very few moving parts, a two-stroke is cheaper to build and maintain than a thumper. The 2009 YZ125 retails for $750 less than a YZ250F.

(2) Weight. At well under 200 pounds, the YZ125 is 18 pounds lighter than a YZ250F. Weight is important to consider when many pubescents can’t lift their own body weight.

(3) Entry-level. Not everyone needs to start racing on a heavy, complex and expensive starter machine. With the 125cc two-stroke gone, the number of people who can easily gain admission to the sport will be reduced.

Q: IF PEOPLE DON’T WANT 125 TWO-STROKES, WHY PUSH THEM?

A: People do want 125 two-strokes, but the AMA made it impossible for them to stick with them. The AMA killed the 125 two-stroke with their stupid rule-making. Then, resisted all requests to fix the displacement formula when it would have made a difference. When they finally did allow big-bore 125s in the 250F class, they immediately made that effort null and void by allowing 250cc two-strokes in the class (making big-bore 125 engines an orphan).

The motorcycle industry is living to regret its silence when 250cc four-strokes were given a massive advantage over 125cc two-strokes a decade ago. Without a low-cost, easy-to-maintain, entry-level race bike, the manufacturers are going to find it harder to get young people into the sport.

Q: ARE THERE ANY CHANGES TO THE 2009 YAMAHA YZ125?

A: You won’t have to sit down to contain your excitement, but there are three changes from 2008 to 2009. This may not sound like much, but in 2008 the YZ125 got eight major changes, including stiffer fork springs, new fork dropouts, smaller YZ250F brake calipers, a redesigned reed spacer, a YZ250F chain guide and more powerful front brake piston. Here are the 2009 changes.

(1) Front brake clamp. Yamaha dropped its oversized, steel, serpentine brake hose holder in favor of a 32-gram-lighter aluminum clamp that looks as though it was borrowed from the DR.D catalog.

(2) Chain. For 2009, Yamaha gets a special zinc-coated chain. It is more corrosion-resistant.

(3) Seat cover. Last year’s gripper seat cover, with its sandpaper-like texture, has been replaced by a woven seat cover that still has gripper potential but without the habit of getting stained.

Q: IS THE 2009 YZ125 FASTER THAN THE 2008 MODEL?

A: No, and it is not faster than the 2007 model either. This is not an old engine and is, in fact, much newer than the Yamaha YZ250F powerplant. Yamaha introduced a brand-new 125cc engine design (with a six-speed tranny) in 2005 (even though the 2004 five-speed engine had also undergone some major mods). The original Yamaha YZ125, the engine that started the ball rolling, was R&D’d in 1994.

Q: HOW GOOD IS THE 2009 YAMAHA YZ125?

A: We love this bike. It is a shame that the YZ125 is on its last legs, because it is as modern, up-to-date and perfected as any motorcycle sold today. It’s a great motorcycle without a place to be raced.

Q: CAN YOU BEAT A 250 FOUR-STROKE ON A YZ125?

A: Of course you can, but it isn’t easy. The YZ125 lacks the torque, hookup, breadth and over-rev to run head-to-head with the much larger four-stroke engines. If a track doesn’t have a long start, hardpack dirt, big hills, off-camber corners, concrete start, fast sweepers or smallish whoops, the YZ125 has a chance. It also has a chance if the YZ125 rider is determined.

Q: WHERE DOES A 125 TWO-STROKE OUTSHINE A 250 FOUR-STROKE?

A: Here is MXA’s list of positive attributes:

(1) You haven’t lived until you’ve ridden flat out on a 125 two-stroke. Nothing compares to its screaming rpm, light weight and six speeds.

(2) With one-tenth the moving parts, you can rebuild a YZ125 four times for the cost of one 250 four-stroke rebuild. A set of pistons, rings and clips for a YZ125 is less than $90. That won’t buy doodly-squat on a YZ250F.

(3) You can pick it up without getting a hernia. It’s a feather compared to the bulky 250Fs.

(4) The snappy engine of the YZ125 allows it to skim across the top of big whoops without dropping in-?the bigger the whoops the better a two-stroke is.

(5) Steep jumps favor the light weight and flickablity of a two-stroke.

Q: WHAT IS THE BEST YZ125 MOD?

A: Before you buy a pipe, port the engine or slip in aftermarket reeds, gear it down. Adding one tooth will perk up second gear, get you to third gear sooner and make the overall ratios between the six gears more user friendly.

Q: WHAT ARE THE BEST YZ125 HOP-UPS?

A: Here is a quick list of things that YZ125 owners can do to make their bikes more competitive.

(1) Bore it out. In the good old days, the most popular big-bore kit was MaxPower’s 139cc kit. It uses a 57mm piston, costs about $925, and is good for about three more horsepower. MXA’s favorite big-bore kit is MaxPower’s 151cc engine. It has a 57mm bore by 59mm stroke and pumps up the volume by four horsepower. It retails for $1950. MaxPower can be reached at (608) 224-2524 or http://maxpower-engines.com/.

(2) Put a pipe on it. Exhaust pipes are a quick and easy way to up the oomph of a 125cc two-stroke. They add about two horsepower and cost a lot less than four-stroke exhaust systems (FMF and Pro Circuit YZ125 pipes cost less than $250).

(3) Porting. Although you have to give to get, a ported YZ125 with head mods is a potent high-rpm weapon.

Q: WHAT ABOUT 2009 YZ125 JETTING?

A: Other than air screw and clip position changes, the MXA test crew had no problems with the YZ125’s stock jetting. Here are the stock YZ125 jetting specs:
   Main Jet: 410
   Pilot Jet: 40
   Needle: 6BFY42-74
   Clip: Third from top
   Air screw: 2-1/4 turns out
   Note: Yamaha delivers every YZ125 with an optional 6BFY43-79 needle and two extra main jets (420 and 430).

Q: HOW GOOD IS THE YZ125’S KAYABA SSS SUSPENSION?

A: Great. Kayaba’s SSS suspension is awesome stuff. There is no doubt that Yamaha’s test department is head-and-shoulders better than any other manufacturer when it comes to suspension settings. For hardcore racing, we recommend this fork setup:
   Spring rate: 0.42 kg/mm
   Oil height: 340cc
   Compression: 11 clicks out
   Rebound: Six clicks out
   Fork leg height: 5mm up
   Notes: Spring rates were upped in 2008, making the bike better suited for hardcore racing.

Q: WHAT WAS OUR BEST SHOCK SETTING?

A: For hardcore racing we recommend this shock setup:
   Spring rate: 4.7 kg/mm
   Race sag: 98mm
   High-compression: 1-1/2 turns out
   Low-compression: 13 clicks
   Rebound: Ten clicks
   Notes: Make small (about 1/8th turn) adjustments to the high-speed compression clicker to adjust the attitude of the chassis at speed. Yamaha’s high-speed compression clicker (the large dial) is very sensitive to adjustment.

Q: WHAT DID WE HATE?

A: The hate list:

(1) Front tire. Love the Dunlop 100/90-19 D756 rear tire, but could live without the 80/100-21 Dunlop 742FA front. It never works as well as specialized rubber.

Q: WHAT DID WE LIKE?

A: The like list:

(1) Suspension. We absolutely love Yamaha’s SSS settings.

(2) Handlebars. Who can complain about oversize ProTaper Contour bars?

(3) Weight. Someday they will build a 250 four-stroke that is under 200 pounds, but until then the 125 two-stroke is the only bike that can make that claim.

(4) Frame. We wish that the Yamaha four-strokes turned their frames inside-out like the YZ125 and YZ250. It looks cooler.

Q: WHAT DO WE REALLY THINK?

A: Every MXA test rider with kids old enough to start racing puts their offspring on 125 two-strokes before letting them loose on 250cc four-strokes. 125’s teach bike handling skills, stress throttle control, and develop racing savvy, while being easy to maintain and sized right for teenagers.