The throttle on my ZXR250 always required an adjustment of my grip to achieve full throttle, which is annoying. I decided to modify the throttle tube (increase the size of the cam) to reduce the distance needed for full throttle. Items needed: A length of 25mm x 1.8mm PVC tubing 8mm & 10mm spanner for throttle cable adjusters JIS screwdriver to undo the switchblock 2 part epoxy Vice plus several clamps Hacksaw or a bandsaw (really handy) Files The first part of any job is measuring. Start with the throttle tube, measuring the width. About 7mm for the ZXR throttle tube Take your 25mm PVC tubing and cut a few 7mm strips off the end You will need to fit the PVC tubing over the throttle tube. This was my first attempt and I cut a little too much out of it for my liking 2nd attempt - pretty much how I wanted it Once happy with your mock fit, mix up some 2 part epoxy. I used a cotton tip to mix and apply. Clamp it in your vice, add some extra clamps to hold it all down and have a cuppa while you wait for the epoxy to harden. I tried superglue on my first attempt which failed, so the epoxy is needed. Once the epoxy was set, I cleaned up the rough sides of the PVC with a file, and slightly filed down the edges I cut where the cables will run. You do not want them to bind up. You will need to completely loosen off both throttle cables and the adjuster on the switchblock/throttle housing when refitting your modified tube, to achieve correct free play. Once adjusted, I measured the length of pull required for full throttle. Roughly 1mm of play Slack tacken up Full throttle Result: Far less effort required for a full throttle turn, no fouling of the cables or PVC against the switchblock - Success! I took the bike for a quick spin around the block to confirm there were no problems. If the standard pull is 90 degrees, my estimation is that it is now in the vicinty of 40-60 degrees of rotation required for full throttle, making it about 1/6 to 1/8 turn.
Thanks, but I can't take credit for the idea. It has been done before and @my67xr suggested it to me as well.
Of course, but it's trial and error, they may be too large to fit the switchblock or not have the change in throttle action that someone wants. Doing it DIY it can be modified to suit your needs or wants.
