performance loss when hot

[ade347]

Hi people, i am having issues with my recently purchased bike I use for work to save on fuel costs.. It's a 2003 peugeot elystar 125 fuel injection, 4 stroke with 5000 miles on the clock, automatic maxi scooter. When it's cold it seems to have good acceleration and top end speed. When it gets to its running temp of 80 degrees after around 15 mins, the acceleration drops off quite noticeably and it struggles to reach its top speed on a length of road it can do with ease when cold. It feels like im suddenly carrying a heavy passenger and only does it when it's 8o degrees or hotter. if you go down hill then onto flat road it maintains its top speed fine but if you start from stationary on a flat road when hot it struggles to get to that same speed.
The engine sounds the same hot or cold, I have checked gap of spark plug which seems fine, it was also a nice brown tint to it. I checked value clearances when it was cold and apart from a quick adjustment of inlet the gaps were almost bang on.
Checked air filter which was fine, a bit of oil in bottom of air filter housing I noticed but put my finger in intake which was bone dry.
A biker friend had a look at it and thinks it sounds fine, but he had a go hot and cold and noticed a difference. its like it's sluggish but the engine sounds fine.
just wondering what next to check/inspect, like I say when its cold performance is fine

[RhynoCZ]

I'd check the belt drive.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[ade347]

Thanks for reply. I kept thinking it was a engine problem but now you say that it has got me thinking. I will take cover off and inspect belt and rollers, not sure how to check the clutch though