ULTRA-SERIOUS RACING FOUR STROKES! - KTM 520 SX, 520 EXC, 400 SX AND 400 EXC

KTM 400 SX is Austria?s answer to the YZ 400. It?s lighter than the Yamaha and at least as fast through the gears.

RIDING IMPRESSIONS ? KTM 400 SX

This is the MX and/or Supercross version of the mid-sized pure racing four-stroke. Much like the 520 SX, the 400 SX was ultra-quick steering and demanded attention when pushing it even at the 90 percent level.

Speed? It seemed to have a lot more low rpm power than the YZ-400, and at least as much mid-range, but the Yamaha revved higher and longer. It weighs the same as the 520 SX, at 235.8 pounds ready to ride, but with no gas in the tank. It?s lighter by a few pounds than the Yamaha and feels much lighter than the 520, even though the scales tell you the truth.

Equipped with a four-speed gearbox like the 520 SX, it?s clear that the 400 is also designed for close-course racing. There?s no way you?re going to gear a close-ratio fours-speeder up for cross country or GP racing. However, like the 520, the 400 will accept a six-speed box, if needed.

I stalled the 400 a few times when landing from a jump because my foot was forced down on the brake pedal from the G-force. If it was my personal bike, I?d find some way to "soften up" that rear brake a bit.

As with the 520 SX, the 400 seemed on the stiff side, suspension-wise. Since the entire quartet of four-strokes shares the same chassis, forks, shock, swingarm, etc., you would think they would all handle the same.

Not so. Each bike had a distinct personality.

For some reason, I did not like the Bridgestone M77/M78 tires that came with the bikes, and genuinely disliked the 19 inch rear wheel on the SX models. On the fun fireroads, those 19 inch rear tires simply did not hook up and the rear end spent a lot of time slithering around, rather than driving the bike forward.

Oddly, the 18 inch tire on the EXC models offered acceptable traction when compared to the 19 incher.

TECHNICAL SPECIFICATIONS

Engine Type;

Single Cyl. 4-Stroke, SOHC/4 Valve Head, Liquid Cooled, Automatic Decompression System

Cylinder;

Mahle Nikasil Coated

Exhaust;

Twin Head Pipe, Two Into One Collector

Silencer;

Aluminum Muffler

Bore and Stroke;

89.0mm X 64.0mm

Displacement;

398ccm

Trans;

4 Speed, SX Close Ratio

Gear Ratios ;

1st - 14:34, 2nd - 17:31, 3rd - 19:28, 4th - 22:

Primary Drive;

30:81

Final Drive;

14 /50, 520 chain

Trans Oil;

SAE 10W-40 wt.; Capacity 1200cc

Spark Plug;

NGKCR8EK

Fuel;

Premium Fuel (92+Octane U.S. Octane)

Fuel Capacity;

7.SL/2.0 U.S. gallons

Carb;

Keihin MX-FCR 39

Jetting;

Main: 175 Idle: 48 Start: 85 Needle: OBDTM Slide: #1 5 Needle Position: #2 Mixture Screw: 1 ½ Turns Out

Ignition;

Kokusan 4K3 Electronic, w/ Lighting Coil 12v 10w

Ignition Timing;

5° B.T.D.C. @ 1000 R.P.M.

Mainframe;

Chrome-Moly

Sub Frame;

Aluminum

Fork;

WP 43 USD, MA

Fork Travel;

295mm/11.6 inches

Fork Oil;

SAE 5 wt.

Rake Angle;

26.5°

Front Brake;

260 mm/10.2" Disc, Brembo Double Piston Caliper, Sintered Pads

Front Tire;

Bridgestone M77 80/100 X 21"

Shock;

WP PDS, External Adjust Compression/Rebound

Rear Wheel Travel;

320mm/12.6 inches

Rear Brake;

220mm/8.65" Disc, Brembo Single Piston Caliper, Organic Pads

Rear Tire;

Bridgestone M78 11 0/90 X 1 9"

Seat Height;

92.5mm/36.4 inches

Wheelbase;

1481 mm/57.3 inches

Ground Clearance;

380mm/15.0 inches

Weight;

107kg/235.8 lbs. (dry)