Posted October 21, 20213 yr Sr125 lacking on power topping out at 40 mph should be 50+. Checked valve clearance, compression and tried fuel air. Power is very jolty at higher Revs. Problem could be fuel air still any help working out if it’s too much or to little fuel or to rich/lean. Any other common problems cause power loss ?.
October 22, 20213 yr Might be worth checking compatibility with the E10 fuel, if that's what you've got in it. It may be buggering up the fuel system
October 25, 20213 yr Moderator Sr's that are fit and healthy can do better than 50. I would (going by the state of my daughters bf bike). You need to check oil, air filter, plug, cap, tyr pressures, chain, sprocket condition and if the brakes are dragging. Everything out of Japan after the mid 90's is capable of running e10 with little more than a mixture tweak. Try some super unleaded. If its the e10 there will be an instant improvement.
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