Modifying the GZ250 - What's Available

[jonathan180iq]

If you're looking for 100mph and a big increase in horsepower, you've come to the wrong place and you're probably riding the wrong bike. The Gz250 will never be a "pull-your-arms-out-of-the-socket" kind of bike. You can however, tweak the exhaust and/or air filter and carb jetting to achieve a slightly better than stock power delivery.

How do I do it?
There is really only one way to increase the power output of any motor vehicle and that is to correctly & proportionately increase the amount of air and fuel that goes into each cylinder. On a carburated machine this is particularly important because increasing the amount of either of these two factors will have adverse effect on the other, if their proportions are not balanced.

For example, as simple a change as having a disconnected crankcase hose will make the bike ping and pop and will leave it basically unrideable over 30 mph. There is a proper balance of the air to fuel ratio and that is 14.7:1
http://en.wikipedia.org/wiki/Air-fuel_ratio

Jaime has an excellent write-up on how to rejet your carburetor when working with a high flow air filter or an exhaust change. Read it thoroughly. Jetting will be different on almost every bike and you need to know what you are doing before you start just taking things apart. That being said, it's not all that difficult, once you know your way around.

See Jaime's write-up here:
viewtopic.php?f=8&t=617

Disclaimer:
Some people consider this mod to be not worth the hassel, as it doesn't provide a mind-blowing difference and takes quite a bit of work. Be sure you know what you are doing before you go in there and screw something up. An imporperly jetted bike is about as much fun to ride as a epilectic cow.