125cc Engine Tuning

So, where do you start with 2-Stroke engine tuning?

Not at the engine, that’s for sure. First things first, your bike has to be in good condition before you start. See the maintenance section for more info, but basically it means ensuring you are not loosing power between the engine and the road. This covers everything from the throttle cable to the tyres, so there is quite a lot to it. But if you are serious about having a fast bike, I believe this first step to be essential. You can loose more than 10% of the engines output power at the sprocket through various parts of your bike.

The main one, and its easy to fix is the chain. If your chain is due for replacement anytime soon, then replace it with the best you can afford. If there is still a good amount of life left, then make sure it is properly adjusted, and well (not over) lubricated.

Next thing to check is the wheel bearings. These should be lubricated, and the wheels should spin freely when the bike is off the ground. These are an often-overlooked part of the bike, but they are important. A quick tip to help your wheel bearings – if you jet wash your bike, don’t spray the water directly into the centre of the wheels, as it may penetrate the bearing and cause corrosion.

While you’re on your knees checking the wheels, have a look to make sure the brakes are not binding. This is when the pads and disk are touching slightly, and this will loose you power. It can happen due to a warped brake disk, or sticking pistons, due to the brake calliper being dirty or damaged.

Tyres are another point of potential loss of power, so should be looked at here. The grip your tyres have is very important to getting the power from the engine down. A worn out or square tyre will decrease forward motion, and cost you power. Check your tyres and their pressures, and if they are on the way out replace them. This will benefit all aspects of your riding, not just help get the power down.

So, that’s pretty much it, but you could have just gained 10% for a couple of hours tinkering with your bike…. now on to the good bit, the real engine tuning.

The tuning of your engine depends a lot on your budget and what you want. It is better to start small and do things gradually, as you can see what works and what doesn’t. It is also important to weigh up the reliability/power ratio. It is no good having a 45bhp missile if your engine needs rebuilding every 500 miles; so keep in mind what the next mod will do to the reliability of your engine. The following starts small and cheap, and gets increasingly larger as it goes on (larger as in more power, but also more cost and possibly more unreliability)