Honda GX160 woes

Hi,
I have a Honda GX160 on a gokart. I'm experiencing a problem, I think it is an air leak. The engine runs on the choke, but once you let the choke off, it sometimes idles slow and sometime high, it doesn't rev up very well and stalls very easily. I've put rtv on the plastic carb insulator and the gaskets which seems to have improved it a little bit but not much. It has a brand new carb as well. I'm thinking it might be a cracked head but before I take it all apart, is there any other causes of this?

Air/fuel mixture screw need tweaked?

I don't think there is one on those carbs. I'll go check now

Edit: There seems to be one. There is an idle screw and beside it there is a slotted brass screw. I'll try adjusting that tomorrow

Nope it's not the fuel/air mixture. I'm thinking either a leaking valve or a cracked head.

Check your valve lash. The rocker arms should be just slightly loose

Good idea. It does make quite a bit of valve clatter when it runs so the valves could be too loose.

Problem solved. It was a combination of a cheap carburettor and a cracked insulator gasket.

I have another problem with another honda, this time a 5.5 clone on a go kart. It is really sluggish off the line and stalls if you rev it too quickly. It's also really hard to start from warm. I've replaced all the carb gaskets which didn't really help. I'm going to try a carb I know works to see if that's the problem.