Everyone has their experience and opinions it seems, but I was just making a suggestion that if he was going to spend $40 on a carb, might as well spend another $60 and get a brand new engine along with a new carb.
Now my Tec may have been near it's end of service life (and it's actually published in the serial number "break down" how long they are designed to last), even with port matching the carb/intake manifold and intake/head (which was pretty far off), I was only able to get 28 MPH out of the Yerf.
Once I installed the HF "clone" engine, I was doing 31.5 MPH right out of the crate. No mods whatsoever.
Not looking for arguement, just posting my personal results.
Terry, there are adjustments for the TAV spring that will keep the kart in "low" gear longer as well as an optional stiffer spring. Those should help with hills a little bit better.
Or there is a 9 tooth sprocket that can be bought to change your final gear ratio as you already read about.
This link should help guide you.
http://www.key-ideas.com/TC-Sprocket-Change.htm