Yz 125 trail bike

[AkYz125Ripper]

So i own a 2003 yz 125, but dont do too much racing. What are some things i can do or get to make it better for trail riding? Heres the stuff i already got:
1. Skid plate
2. Go up 2-3 teeth on the rear sprocket
3. Hand guards
4. Larger fuel tank
5. Switch to br8es instead of the br9es race plug
6. New expansion chamber ("fatty"), anyone have any suggestions on a good one thatll help with trail riding? I have thought about getting a fly wheel weight and am not really liking the sound of it. I like the light response of the throttle as it is and im pretty good about keeping it in the power band a lot.

 

[SRAD97750]

One thing not mentioned yet is Base gasket/Port Timing. Also Engine Ignition Timing.
Some top end gasket kits come with 3-4 different sizes of base gasket to give your engine slightly different port timing. A thicker base gasket can smooth or move the "hit" lower in the rpms making it easier to trail ride.

Retarding the engine ignition timing slightly can also achieve this. (Though, not all bikes have adjustable stators)
If yours does, Just loosen the screws on the stator and rotate it slightly in the direction of engine rotation. Then re-tighten the screws. -BIG DAN

 

[2strokesteve89]

the suspension set up is usually stiffer on a mx bike than what most people like for the trail, I'm one that likes the stiffer suspension for trail or track, but you may want to experiment with different settings on you shock and forks, for whatever trails you'll be on.just keep track, maybe on paper, how you changed your adjustment, so you know what way to go next time. or get back to your starting point.

 

[snowflake]

the suspension set up is usually stiffer on a mx bike than what most people like for the trail, I'm one that likes the stiffer suspension for trail or track, but you may want to experiment with different settings on you shock and forks, for whatever trails you'll be on.just keep track, maybe on paper, how you changed your adjustment, so you know what way to go next time. or get back to your starting point.

The faster you ride the stiffer you'll want the suspension.

OP- If you're just starting out I'd set your sag on the rear shock, and try turning down the comrpession and rebound 2 clicks at a time to see if that helps you feel comfortable.

I'd also go 1 tooth smaller on the rear as opposed to larger on the rear.

 

[ossagp]

For my yamahas one tooth smaller on the sprocket affects the drag too much. I go up on both ends sizewise. getting one larger than a 53 usually results in ordering from Sprocket Specialties though. I use a 14 and a 56 for some riding and that requires that the chain guide be modified.

In the end, if you stick with the 5 speed you are going to be 'wanting' for a lot.

The over bored 125's I have make pretty good trail bikes. I have one that is a lot like a fast, light KDX with closer ratio gears as far as the engine goes. (It is a yamaha with a 144 kit that started life as an athena 125).

As far as going up or down on the cylinder height, the larger bikes can go "up" a little and live ok with the more advanced and longer port timing easier than the 125's can. My trail ridden 144 is quite a bit retarded in the port timing from stock. Going to a thicker base gasket does just the opposite. I would try thinner if you are going to try a different gasket thickness.

I would be looking hard for a 6 speed gear set above anything you listed as prospective or already done. It will really add to the versatility of a 125. track only you can easily live with and can probably even prefer the 5 speed.

 

[ossagp]

One thing not mentioned yet is Base gasket/Port Timing. Also Engine Ignition Timing.
Some top end gasket kits come with 3-4 different sizes of base gasket to give your engine slightly different port timing. A thicker base gasket can smooth or move the "hit" lower in the rpms making it easier to trail ride.

Retarding the engine ignition timing slightly can also achieve this. (Though, not all bikes have adjustable stators)
If yours does, Just loosen the screws on the stator and rotate it slightly in the direction of engine rotation. Then re-tighten the screws. -BIG DAN

It's ok Dan. But I bet you havent tried retarding ignition timing or advancing/increasing duration port timing on a 125 yet, have you?

 

[Mihylo33]

Save your coin and just go down 1 tooth on the sprocket, and ride 1 gear lower than you normally do. Spend the saved money on premix and hair gel.....