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Other than that; make sure your jetting is spot on, squish is good, packing fresh, air filter clean, and spark plug is fresh.
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Gear it down atleast two teeth. Heck if you really want a peppy lowend gear it down three teeth.
125'a have enough topend you'll barely notice any small loss in topend ..I rode a friend's sons very 85that had three teeth lower gearing and iI couldn't hardley keep the front end down.. it was a little torque monster...it was awesome.
Paging tuned length to the white courtesy phone.
Buy a compression tester at sears or autoparts store ,screw it in plug hole but leave the sparkplug in the boot and let it lay on the head so it will be grounded and make its spark so not to overload the ignition,this or hold the kill button down.
Now hold the throttle wide open and kick the starter till the gauge stops rising. On a 125 you should be around 200 psi.
I bet it is going to be in the 150 psi range. The tc probably has a selection of base gaskets,go with the thinnest to get compression up as much as possible that way.
If it is still low the head can be milled to raise it. This is a little technical because the squish band needs to be reshaped so the firing charge is centered over the middle of the piston.
A 125 will loss topend rpm if the compression is taken really high so mill in increments till the best is reached,if you go to far the combustion dome can be milled some to lessen compression and keep the squishband correct.
By the way,what octane fuel are you using now?
Use the l lowest octane you can and not have the bike ping or preignite.
Race fuel in a stock,low compression engine will make the lowend soft.
I should have asked about fuel octane first
You ever see guys run longer silencers in SX? Long silencers are at home in the great outdoors and the shortys for the bottom end, snappiness. Tried and true testing on my former YZ-250 2t's made this real evident. They don't rev out nearly as far with a shorty. If you wanna do a quick redneck check (no offense, to those crimson anatomy'd folk), take your silencer off and see how much low end you have
I've played around with the valve but honestly I think the factory setting is best.
Everyone saying to gear down... You're just wrong. These bikes are geared short enough as it is, a bigger rear sprocket is gonna make the gears too short as someone else said.
Pit Row
One more easy thing to do is to disconnect grey wire under the thank. This will give you mellower ignition curve and engine is little easier to ride. I would also try heavier flywheel from enduro model.
This is why you need to check compression psi.
The most power will come from 87 octane fuel up to the point the compression makes it pre ignite.
If you set one to sit and idle it is to lean ,makes the initial hit of low rpm soft.
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