Polaris galaxy 440

I just bought a '80 Polaris galaxy 440 and I put a new throttle cable on it. Now when I accelerate I can get up to about 10mph but when I push the throttle all the way in it boggs down to an idle. I spent about 5 hours adjusting the throttle and the carbs but its not making a difference. I'm starting to think it might be a clutch problem but I'm not sure so any help would be greatly appreciated,

Thanks.

Polaris galaxy 440