Jeff Fredette at Fredette Racing Products has been racing KDXs for over 20 years and has learned a lot about how to modify them to fit your specific needs. Here's some of the answers to the most frequently answered question. For more information check out Jeff's web page here: Fredette Racing Products .
Engine Performance
1983-1985
The stock pipe works best with Answer SA silencer. The cylinder ports should be cleaned and matched. The carburetor jetting should be as follows: 1983, 150 Main jet; 1984-85, 35 pilot and 280 main jet.
1986-1988
Changing the silencer has the biggest performance improvement. The Answers SA works well with a FMF pipe. Cylinder porting (clean and match casting and match port heights) will tame the hard hit and give more low and top end. Carburetor jetting should be as follows: 1986-87 models. 30 pilot jet, p-2 needle clip position, 330 main jet; 1988 model, 48 pilot jet, p-3 needle clip position, 155 main jet. When performing top end rebuild the factory service manual does not explain the KIPS timing procedure. The dot marks on the drum valve align with the ring mark on the actuator rod (rack). To check your work when the actuator rod is pulled to the stop the valves should be open and when pushed in the valves should be closed.
1989-1994
These modifications work best to improve the powerband over the entire rev range: FMF pipe and straight through silencer, Boyesen RAD valve, cylinder porting. Carburetor jetting; 48 pilot jet, 1173 needle in the middle clip and 155 main jet and turn the air screw out 1.5 – 2 turns.
1995-2003
The 1995 year was the first year of the KX style exhaust valve system. The new design utilizes a wedge for the main exhaust port. The design enables better control of the effective stroke and compression ratio over a wider RPM range. The best mod is an FMF pipe. If you need top run a spark arrestor try the FMF or Acerbis 035. The next mod to consider is cylinder porting. The cylinder needs the cast marks polished and smoothed for more power throughout the power range especially on the top end. A Boyesen RAD valve gives a modest gain in performance. If you are having troubles with clutch slippage switch to stiffer clutch springs: Kawasaki OEM #92144-1484. Run the transmission oil high on the sight window. This will help reduce the noise from the clutch side of the engine.
Front Suspension
1983-1985
Use the stock springs for riders up to 180 pounds. Over that use .32Kg springs with 5-weight oil and a fork oil level of 5.5 inches measured with the springs out and the forks bottomed.
1986-1988
The best fork oil weight is 7.5 (mix 5 and 10 wt 50/50). Run oil level between 4.75 and 5.5 inches. The forks are Characteristically harsh on small rocks and for best performance they need to be revalved. Use of progressive fork springs is recommended on all models for riders over 175 pounds. The stock fork springs sag over time. The maximum distance a spring should sag under the bikes own weight is ¾ inch.
1989-1993
These forks are a little soft. Switching to a heavier fork spring makes a big difference. For riders up to 170 pounds we recommend .33 Kg springs from the 1988 KDX. For heavier riders we recommend progressive springs 18 to 26 lbs. try setting the compression adjusters 6 to 11 clicks out. If that set up is not to your liking, try revalving.
1995-2003
Stock forks are set up for 130-pound rider. For riders between 140 and 190 pounds switch to 21 pound spring, for riders over 200 pounds, use the 23-pound springs. Set the oil level at 100 mm and compression adjuster between 10 and 18 clicks out. The Race Tech Gold Valve kits works well with Fredette shim placement specs.
Rear Suspension
1983-1985
Use stock spring and set the damper to position #2 for fast riding such as whoops and position # 3 for slower riding over rocks. I set the sag to ½ inch unladen (the bikes own weight only) for riders under 175 pounds and ¼ inch for riders over 175 pounds.
1986-1988
Use the stock shock valving. The settings that work best are ½ inch unladen (the bikes weight only) sag for most riders and no sag for riders over 200 pounds. Compression damping setting s were best at 3 clicks out on fast whooped out courses and 12 on slow riding over rocks. Run rebound adjuster at 2.5 turns out. Have the shock oil changed frequently (every 100 miles) to prevent shock shaft wear.
1989-1993
The stock spring and valving work OK if dialed in correctly. Start with a fresh oil change and set the sag to 3.75 inches (with rider and full fuel tank). Set the compression clicker for 6 out on fast terrain and 10 out in slow terrain. Set the rebound clicker for 8 for fast terrain and 10 for slow terrain.
1994-2003
The stock spring and valving work well for riders 170-200 pounds. If you are lighter or heavier than that you would benefit from a different spring. Lighter riders should use a 4.8-Kg spring and heavier riders should use a 5.2-Kg spring. Set compression 8 clicks out for fast terrain and 16 clicks out for slow terrain. Set the rebound adjuster in the same way more damping at higher speeds.
Engine Performance
1983-1985
The stock pipe works best with Answer SA silencer. The cylinder ports should be cleaned and matched. The carburetor jetting should be as follows: 1983, 150 Main jet; 1984-85, 35 pilot and 280 main jet.
1986-1988
Changing the silencer has the biggest performance improvement. The Answers SA works well with a FMF pipe. Cylinder porting (clean and match casting and match port heights) will tame the hard hit and give more low and top end. Carburetor jetting should be as follows: 1986-87 models. 30 pilot jet, p-2 needle clip position, 330 main jet; 1988 model, 48 pilot jet, p-3 needle clip position, 155 main jet. When performing top end rebuild the factory service manual does not explain the KIPS timing procedure. The dot marks on the drum valve align with the ring mark on the actuator rod (rack). To check your work when the actuator rod is pulled to the stop the valves should be open and when pushed in the valves should be closed.
1989-1994
These modifications work best to improve the powerband over the entire rev range: FMF pipe and straight through silencer, Boyesen RAD valve, cylinder porting. Carburetor jetting; 48 pilot jet, 1173 needle in the middle clip and 155 main jet and turn the air screw out 1.5 – 2 turns.
1995-2003
The 1995 year was the first year of the KX style exhaust valve system. The new design utilizes a wedge for the main exhaust port. The design enables better control of the effective stroke and compression ratio over a wider RPM range. The best mod is an FMF pipe. If you need top run a spark arrestor try the FMF or Acerbis 035. The next mod to consider is cylinder porting. The cylinder needs the cast marks polished and smoothed for more power throughout the power range especially on the top end. A Boyesen RAD valve gives a modest gain in performance. If you are having troubles with clutch slippage switch to stiffer clutch springs: Kawasaki OEM #92144-1484. Run the transmission oil high on the sight window. This will help reduce the noise from the clutch side of the engine.
Front Suspension
1983-1985
Use the stock springs for riders up to 180 pounds. Over that use .32Kg springs with 5-weight oil and a fork oil level of 5.5 inches measured with the springs out and the forks bottomed.
1986-1988
The best fork oil weight is 7.5 (mix 5 and 10 wt 50/50). Run oil level between 4.75 and 5.5 inches. The forks are Characteristically harsh on small rocks and for best performance they need to be revalved. Use of progressive fork springs is recommended on all models for riders over 175 pounds. The stock fork springs sag over time. The maximum distance a spring should sag under the bikes own weight is ¾ inch.
1989-1993
These forks are a little soft. Switching to a heavier fork spring makes a big difference. For riders up to 170 pounds we recommend .33 Kg springs from the 1988 KDX. For heavier riders we recommend progressive springs 18 to 26 lbs. try setting the compression adjusters 6 to 11 clicks out. If that set up is not to your liking, try revalving.
1995-2003
Stock forks are set up for 130-pound rider. For riders between 140 and 190 pounds switch to 21 pound spring, for riders over 200 pounds, use the 23-pound springs. Set the oil level at 100 mm and compression adjuster between 10 and 18 clicks out. The Race Tech Gold Valve kits works well with Fredette shim placement specs.
Rear Suspension
1983-1985
Use stock spring and set the damper to position #2 for fast riding such as whoops and position # 3 for slower riding over rocks. I set the sag to ½ inch unladen (the bikes own weight only) for riders under 175 pounds and ¼ inch for riders over 175 pounds.
1986-1988
Use the stock shock valving. The settings that work best are ½ inch unladen (the bikes weight only) sag for most riders and no sag for riders over 200 pounds. Compression damping setting s were best at 3 clicks out on fast whooped out courses and 12 on slow riding over rocks. Run rebound adjuster at 2.5 turns out. Have the shock oil changed frequently (every 100 miles) to prevent shock shaft wear.
1989-1993
The stock spring and valving work OK if dialed in correctly. Start with a fresh oil change and set the sag to 3.75 inches (with rider and full fuel tank). Set the compression clicker for 6 out on fast terrain and 10 out in slow terrain. Set the rebound clicker for 8 for fast terrain and 10 for slow terrain.
1994-2003
The stock spring and valving work well for riders 170-200 pounds. If you are lighter or heavier than that you would benefit from a different spring. Lighter riders should use a 4.8-Kg spring and heavier riders should use a 5.2-Kg spring. Set compression 8 clicks out for fast terrain and 16 clicks out for slow terrain. Set the rebound adjuster in the same way more damping at higher speeds.
