Problems with 7150 150 cc

[Mudpuppy]

Have a 7150 150cc gokart, starts good, runs good, no problems on flat ground but when u start up an incline with with bog down to a complete stop can push it till flatter ground off it goes again. My daughter is only 9 and she can't pull the smallest incline unless she gets a good run at it. What could be the issues.. please and thank you.

[Mudpuppy]

I'm located in the country not no major hills... I was told to check the driver pulley and the drivin.

[Mudpuppy]

Changed rollers and 2000 rmp spring to the yellow 1500 spring and 10g rollers still will not climb hill.... please help