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2011 YAMAHA YZ125 TEST: ARE YOU LOOKING FOR A MOTOCROSS BIKE THAT CAUSES YOU TO GIGGLE WHILE GOING WIDE OPEN? THIS IS IT

December 1, 2010
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2010 YZ125 action

Q: FIRST AND FOREMOST, IS THE NEWEST YZ125 BETTER THAN THE PREVIOUS YZ125?

A: No. It is the product of Xerox engineering.

Q: WHAT ARE THE MAJOR CHANGES THAT YAMAHA MADE TO THE LATEST YZ125?

A: There are none. The graphics on the gas tank are different?if that counts as a major change.

Q: IS THE NEW YZ125 FASTER THAN THE OLDER MODELS?

A: This is MXA‘s 2010 Yamaha YZ125 test, but the info in this test in applicable to the 2009 and 2011 models. Is the 2010 YZ125 faster than last year’s YZ125 or next year’s YZ125? No, and it is not faster than the 2007, 2008 or 2009 model, either. In truth, most 125cc technology was frozen in place back in 2005. It should be noted that the 2010 and 2011 YZ125s engines have a newer design than the 2010 YZ250F four-stroke engine.


yz125 carb   yz125 engine
Vergasser: Mikuni doesn’t get much play in motocross, but the YZ125’s jetting is spot-on with its old-school carb. Price tag: With little more than the occasional piston, a YZ125 requires very little in the way of maintenance or hop-ups.


Q: HOW DOES THE YAMAHA YZ125 RUN ON THE DYNO?

A: It makes 34.01 horsepower. How does that compare to other 125s? There aren’t any other 125cc motocross bikes coming out of the Big Five manufacturers. KTM was the last major competitor that Yamaha had, and the Austrians don’t import the KTM 125SX to the U.S.A. anymore?preferring to bring in the big-bore 150SX model. In a strange case of import/export envy, you can still buy a Suzuki RM125 on other continents.

The only viable comparisons for the YZ125 are the 250 four-strokes and the KTM 150SX. The Yamaha YZ125 makes 3 horsepower less than both the 250 four-strokes and big-bore Katoom (and it produces that power over a much narrower powerband).

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

    
A: It can be done, but it isn’t easy. When you match the YZ125 up against a machine with twice the displacement (especially one with more torque, increased rev and more breadth), you don’t get a fair fight. Yet, YZ125 riders can run down 250cc four-strokes when the conditions are right.

What are the right conditions? A track with a short start, loose loam, small hills, minimal off-cambers, a dirt starting line and tight corners will make life easier for a YZ125. Conversely, long starts, rock-hard dirt, big hills, concrete starting pads, off-camber corners and sweeping turns will favor the bigger, torquier and higher-revving four-stroke.

Q: HOW GOOD IS THE YAMAHA YZ125 TWO-STROKE?

A: We love this bike. As with its YZ250 brethren, the YZ125 has been developed to the nth degree. It is the perfect expression of functional engineering.

In Europe, they have started an all-new 125cc European Motocross Championship, and some American tracks offer 125cc two-stroke classes, but with fewer and fewer 125’s being produced each year, there is less interest in racing them. Thus, the perfect machine has no place to race.

yz125 side shot
2010 Yamaha YZ125: In truth, the YZ125 has been relegated to the status of an entry-level race bike by AMA rules. It is a great bike, but it doesn’t have a home to call its own.

    
2011 Yamaha YZ125: If you are looking for differences between 2011 and 2010?look at the decals on the radiator wings and a yet-to-be announced longer silencer.

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.

Big-bore kit. With the exception of 125cc-only classes, the MXA wrecking crew saw no reason to stick with the traditional displacement. So, we beefed up our YZ125 with a GYTR YZ144 kit. The kit includes a brand-new nickel carbide-plated Athena cylinder, cylinder head, 58mm piston (with rings, pins, clips, gaskets), modified Power Valves, O-rings and complete instructions. Best of all, it fits all 2005-2010 Yamaha YZ125 models. The retail price is $859.95. There is one caveat: It requires some grinding on the center cases. It is available through your local Yamaha dealer.

Gearing. Before you buy a pipe, port the engine or slip in aftermarket reeds, gear the YZ125 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.

Pipe. Exhaust pipes are an easy way to add power. They add about 2 horsepower to a 125cc and cost one-third of what four-stroke exhaust systems cost. FMF and Pro Circuit YZ125 pipes cost less than $250.

Porting. A ported YZ125 (with head mods) is a potent, high-rpm weapon. The cost to port the cylinder and mill the head is typically around $329.95. Contact Pro Circuit at www.procircuit.com.

Reeds. We run a Boyesen RAD valve to broaden the power. The $179.95 RAD valve is a complete replacement reed block and valve assembly. Boyesen can be reached at www.boyesen.com or at (800) 441-1177.


If you can only afford one mod?add one tooth to the rear sprocket. You’ll feel the difference.

Q: HOW GOOD IS THE YAMAHA YZ125’S JETTING?

A: The MXA test crew had no problems with the YZ125’s stock jetting. Here are the stock YZ125 jetting specs:
   Mainjet:
410
   Pilot jet:
40
   Needle:
6BFY42-74
   Clip:
3rd from top
   Air screw
: 2-1/4 turns out
   Note:
Yamaha delivers every YZ125 with an optional 6BFY43-79 needle and two extra mainjets (420 and 430).
 
Q: WHAT WAS OUR BEST FORK SETTING?

A: Kayaba’s SSS suspension is incredible. It can be raced right off the showroom floor. For hardcore racing, we recommend this fork setup:
   Spring rate:
0.42 kg/mm
   Oil height:
340cc
   Compression:
11 clicks out
   Rebound:
6 clicks out
   Fork
leg height: 5mm up   
   Notes:
If you are very light (under 150 pounds), you might want to replace the stock 0.42 kg/mm springs for the softer 0.40 kg/mm fork springs that were used prior to the 2008 model year. In most cases, however, spring or valving changes are not necessary on Kayaba’s SSS suspension components.

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
   Hi-compression:
1-1/2 turns out
   Lo-compression:
13 clicks out
   Rebound:
10 clicks out
   Notes:
Make small (about 1/8 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.


 yz125 bars  
Handling: Compared to the YZ125 a 250cc four-stroke is a pig. The weight difference is 18 pounds. Moving parts: A proven design, the 2010 YZ125 is bulletproof. Virtually every wrinkle has been ironed out over the years.


Q: WHAT DID WE HATE?

A: The hate list:

(1) Front tire. We love the Dunlop 100/90-19 D756 rear, but could live without the 80/100-21 Dunlop 742FAL front.

(2) Plastic. We know there is a recession going on, but how about updating the fenders, gas tank and radiator shrouds to look more modern. How hard would that be?


It’s so light that it makes everything else seem porcine.
    
Q: WHAT DID WE LIKE?

 
A: The like list:

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

(2) Suspension. We love Yamaha’s SSS settings.

(3) Handlebars. Pro Taper Contour bars. ‘Nuff said.

(4) Weight.  At well under 200 pounds, the YZ125 is 18 pounds lighter than a YZ250F. Weight is important to consider when many young riders aren’t strong enough to lift their own body weight.

(5) Entry-level. Heavy, complex and expensive 250cc four-strokes are not the best machines to start a racing career on. A 125cc two-stroke is the perfect size machine for a minicycle transplant.

Q: WHAT DO WE REALLY THINK?

A: The Yamaha YZ125 two-stroke, whether a 2009, 2010 or 2011, is a bike that teaches bike handling skills, throttle control and race savvy. It is the optimal vehicle for a neophyte to learn the ins-and-outs of motorcycle racing on. Unfortunately, it has been relegated to the play bike category by rule changes.

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