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125cc - not going fast enough


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Last week I have bought KSR Moto GRS 125 (2016), only 2885 miles.

Using the bike mainly to go to work 15-20min ride. But the bike got problems going up the hill, up the hill im going only 40mph, where traffic is going 50mph. So its not really safe when cars are overtaking you all the time.

On 3rd gear im able to go about 40mph, but when going on 4th gear its just slowing down.

The bike goes to 30mph pretty fast, but after that it take time.

I have changed the oil, checked the oil filter, cleaned the air filter, cleaned the carburetor, checked if jets are clocked and checked clutch.

What could be the issue here ?

Could it be the issue with the carburetor ?

Will adjusting it give more power or something ?

Will new exhaust give it more power ?

Will bigger rear sprocket make it reach 50mph+ easier ?

Im 98KG if something.


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A common issue due to the lack of torque. The usual fix is to reduce the front sprocket by one tooth size. This brings the engine rpm up in each gear enabking it to be closer to it's maximum power output at higher speeds.

You will lose theoretical top end speed but that only applies going downhill with wind behind you anyway.

Going up a couple of teeth at the back can achieve the same result. Most 125s are over geared from the factory.

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How does one check an oil filter may I ask? :|

Change the oil and the oil filter I think you meant. 60mph is the top speed, 40mph with 20kg more than what I have would probably be right if it's a steep hill. Make sure the tyres are correctly inflated.

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