FIRST LOOK AT THE TWENTY-TEN YAMAHA YZ250F:

FIRST LOOK! TWENTY-TEN YAMAHA YZ250F:
26 THINGS YOU DON’T KNOW ABOUT THE 2010 YAMAHA YZ250F?

    (1) All-new straight/smooth intake boot has been added to improved throttle response. The shock spring was moved to clear a path for the new air boot.

2010 YAMAHA YZ250F JETTING
Main jet: 178………….180
Pilot jet: 42…………….45
Needle: NHKR-4…….NDJR-4
Leak jet: 70……………70
Fuel screw: 2…………2-1/4
 
    (3) Intake cam lift is changed from 7.6mm to 7.7mm (cam timing is same as ’09).

    (4) Chromium nitride surface treatment is added to valve stem to improved durability, lessen valve adjustment and improve throttle response.

    (5) Valve spring retainers changed from steel to aluminum.

    (6) Valve spring load is reduced which allows for lighter valve spring rates. The intake valve spring load is 12 percent less, while the exhaust spring load is nine percent less.

    (7) The exhaust port shape is changed from round to a D-shape design. Exhaust port volume is reduced to increase exhaust velocity and improve low-end power.

    (8) The new exhaust system has a two-step design (going from 45.0mm head pipe to 50.8mm midpipe. The muffler is 50mm longer. The core diameter is reduced from 42.7mm to 41.3mm. The perf core has the holes placed farther apart, but because of the 325mm log muffler there are the same number of holes as last year. The muffler is no longer rubber mounted.

The 2010 muffler (top) is 50mm longer than the 2009 muffler (bottom).

    (9) The clutch actuation arm’s cam ratio is increased is by nine percent, while the clutch springs are six percent stiffer. Overall the clutch pull is three percent lighter. Additionally the clutch baskets center boss has a harder material for more durability.

    (10) Third and fourth gear ratios are taller.

YAMAHA YZ250F GEAR RATIOS
Gear   2009…….2010
3rd:    1.450……1.444
4th:    1.227……1.222
 
    (11) The aluminum bilateral beam frame (think perimeter frame) uses 20 pieces of forged and extruded components i its design. The old aluminum frame used eight pieces and had some castings).

    (12) The steering stem pipe is moved 12mm and lower and 7mm back.
 
    (13) The head angle has been changed from 27.2 degrees to 27.5 degrees. The trail has been increased from 117mm to 120mm.

    (14) The new frame is more rigid under a twisting or horizontal load and about the same as the 2009 frame vertically.

The 2010 perimeter frame is on the left and the 2009 single backbone frame is on the right.

    (15) The head stays now mount on the side of the cylinder and use straight pieces of aluminum. Last year the head stay had S-bends in them.

    (16) The remote oil tank is smaller and lighter. It holds 100c less oil than in 2009. The oil sight glass is now located in the correct spot (in 2009 it as 200cc too low).

    (18) The top steering head bearing has a new heavy-duty rubber seal to keep water out.

    (19) The Kayaba Speed Sensitive System (SSS) front fork has new damping settings with more low -speed damping, new forks seal shape and a frictionless surface treatment on the piston rod.

    (20) The Kayaba shock spring is 30mm lower to make room for the new intake boot. The damping is stiffer to handle the new chassis’ rigidity.

    (22) The footpegs are 5mm higher and the seat is flatter and further forward.

    (23) There is a new brake pedal and kickstart lever to fit the new frame design.

    (24) The skid plate is plastic and has built-in case guards. The skid plate was changed from aluminum because the aluminum skid plate effected frame rigidity negatively.

    (25) The all-new plastic is called “arrow styling.” It is very pointy.

The fenders are very pointy. The 2010 front fender on on the left.

    (26) The 2010 YZ250F is available in traditional blue or white with red trim (and black rims).

IN THE FOLLOWING PHOTOS THE 2010 PARTS ARE ON THE LEFT AND THE 2009 PARTS ARE ON THE RIGHT