Engine Tips

There are a number of engine performance products and services available for all KDX models which I have tried and would recommend. Because everyone operates on a different performance need and budget I have decided to list my recommendations in the most logical and economical sequence:

1989-1994 "E" Models: The first modification I would recommend is to replace the stock exhaust pipe and silencer with an FMF pipe and a POWERCORE II or TURBINECORE II Silencer. While both silencers will perform comparably, the POWERCORE II model is designed for closed courses and the TURBINECORE II "spark arrestor" model is required at all government regulated riding areas. At the same time I would recommend replacing the stock jetting with a 45-48 PILOT JET, a 152-158MAIN JET and an 1173 NEEDLE set in the middle position with the air screw adjusted out .5-1 turns. These simple and fairly inexpensive modifications will noticeably improve the performance of your KDX throughout the power band.

If you still want more power from your KDX I would recommend that you SEND us your cylinder so we can work our magic on its ports. This modification will provide even greater performance throughout the power band with more revs on top. After making this modification I would recommend replacing the stock jetting with a 45-48 PILOT JET, a 152-158MAIN JET and an 1173 NEEDLE set in the middle position with the air screw adjusted out 5-1 turns.

Still want more low-end throttle response and performance throughout the power band? Then I recommend replacing the stock reed valve with a BOYESEN RAD VALVE. If it's more bottom end performance you want I would recommend installing an FRP TORQUE RING. This small device will boost bottom end performance at the expense of only a couple hundred rpm's from the top. No additional jetting changes are required with either of these modifications.

1995-2006 "H" Models: The first modification I would recommend is to replace the stock exhaust pipe and silencer with an FMF Pipe and Silencer. There are two pipes available. I recommend the Gnarly "REV" PIPE for the more experienced rider and all other riders riding in fast terrain with good traction. This pipe will improve performance throughout the power band with the most noticeable hit in the mid-range and up. I recommend the GNARLY "TORQUE" PIPE for the less experienced rider and more technical terrain because it also improves performance throughout the power band but with a more manageable power delivery. The torque pipe is not recommended for the 220’s. There are also two silencers available. While both silencers will perform comparably, the POWERCORE II model is designed for closed courses while the TURBINECORE II "spark arrestor" model is required at all government regulated riding areas No jetting changes are required with this modification. These simple and fairly inexpensive modifications will noticeably improve the performance of your KDX throughout the power band.

If you still want more power from your KDX I would recommend that you SEND us your cylinder so we can work our magic on its ports. This modification will provide even greater performance throughout the power band with more revs at the top. After making this modification you may need to replace the stock jetting with a 45-48 PILOT JET and a 155-160 MAIN JET. For 220 Models Only: You can improve low end throttle response and add even more top end performance to this model by letting us work a little extra magic on your cylinder head and carburetor. Just SEND us these components with your cylinder and we will turn your 220 into a machine that even your 250 buddies will admire!

Still want more low-end throttle response and performance throughout the power band? Then I recommend replacing the stock reed valve with a BOYESEN RAD VALVE. If it's more bottom end performance you want I would recommend installing an FRP TORQUE RING. This small device will boost bottom end performance at the expense of only a couple hundred rpm's from the top. No additional jetting changes are required with either of these modifications.