ya i have a 2003 yz 125 and i mostly ride trails but sometimes i do motocross and i usually have a really hard time on the trails because it is mostly bogging with no power :| any tips for that. thanks
i almost only trail ride with 00 kx125 you just have to keep the motor on the power band and spinnin fast or else you'll start boggin. if your going to jet it though do it yourself, factory and aftermarket manuals have the procedure. buying jet "kits" can get dangerous because they may be made for a different pipe etc. just get an assortment of jets and do it yourself youll have a better end result.
Depends, it is not vital to do but if you want to keep the same chain size and gear lower than you would "distribute your teeth accordingly". For example if you dropped a tooth in the front than you would go up a tooth in the back. So basicly what you loose in the front you gain in the back or.
You will see a big difference with just going 2 teeth. I think 3 is too much (constantly shifting) If you ever do some porting work for woods riding, that will give you more low-end........which may make you want to go back to stock gearing or +1 tooth in the rear. Less countershaft teeth, or more rear teeth will always move the gears closer together too, meaning more shifting. Motor work is a solution, gearing is a bandaid fix on a 125.