Used scooter lacks power.

[SunSpine]

Hello. I did a few searches and couldn't find anything exactly like what is happening with my scooter. I was hoping someone could help.

I bought a used scooter. It is marked a Venture ZN150T-7C. The engine is labeled BN157QMJ. It's a 2008 with about 2,400 miles on it.
My issue is that this scooter should go about 65 mph, but I can't seem to get it above 35 in an ideal flat situation. This scooter only goes about 18 mph hour up hills which is a problem for the commute I intend to use it for.
I replaced the engine and gear oil and that is when the top speed went up to 35. Now I need to know what the next step is.
Thanks.

[dwint51]

I would start by looking at your plug.your carb must be way off.does it start ok?idle?how about when its running?you never know what your buying when you buy used.they could of disconnected the speedo for thousands of miles and reconnected it.you just have to check out everything one by one.compresion test?

[kz1000st]

I would look and see if there is a vacuum line off somewhere. What does the scooter do at 35 mph? If it bucks and stumbles it could be a mixture problem. It could be the rollers aren't moving fully in the variator. It could be a torn diaphragm in the carburetor. Many things could be at work here.

[SunSpine]

Thanks guys. I'll check all this out tomorrow and update what I find.

[SunSpine]

I found the main hose from the air filter to the carburetor had lots of cracks and holes. After I fixed that the scooter is running so much better. Thanks for the help.