Hello

I tried searching but came up empty so here goes. I'm renting a yamaha mio 125 gtx, the bike has been around the block a few times but has done 400km now pulling like a horse. Amongst other the Pai roads.

Now in Mae Sariang the bike is losing power up hill or when going faster than 60kmh. I have only used gas station gas and it's no different on low, med or full tank. I did some back and forth with the rental company and a local mechanic but their diagnosis is "high altitude" (or possibly fat farang on small bike).

Idle is fine but trying to push it more than crusing and there is a noticeable lack of power. Am i just paranoid (and to fat) or might there be something to be done?

Lack of power or lack of speed?

Does the engine rev but it doesn't go any faster?

drive belt is worn out

Or

Does the engine bog and not reach maximum RPM.

Could be a dodgy spark plug get them to puty a new one in

Could be air fliter plugged take it out and try again. It is in the black box on the left hand side.

Could be a blocked fuel filter if there is one.

Could be a blocked jet/injector ( I don't know if 125 GTX is carburettor or injection)

The key to diagnosis is "what has changed"?

The hill gradient?

The fuel?

If it is a fat farang on a bike ask them (svelte Thai mechanic) to ride it up the hill?

It's A125cc.If ya want to go up A hill faster he A bigger engine.

Check for way overfull oil. Best way is change the oil and add the appropriate amount. (From experience.)

Get a Honda~~~

I know it's a 125, im not expecting wonders from it. I leathermaned it and shook out some shit from the airfilter but i think just letting the bike cool down over night had more of an effect. Drove 230kms today in much cooler weather and it ran more or less like expected. So heat and paranoia might have been the problem after all.

So heat and paranoia might have been the problem after all.

Well it is air-cooled so will suffer if it gets very hot. Add to that the uphill especially if the motor is working hard and it is constant uphill for miles.

In Indonesia I used to see guys pushing their over loaded venerable Honda "Waves" up hills. OK they are not fan cooled but...

For example a stock PCX with a 125 motor will do in indicated 110 on the flat but will only achieve 76 kph on a 5% grade this is with a 75 kg rider. So if the grade is more or the rider heavier the speed will be less. But once back on level ground the speed should go back up to 110. If yours does not not go back to the diagnostics.

If it was yours and not rented adding an oil cooler etc but even then...