I agree putting up with the problem is better than shelling out for an su, but sometimes it gets very frustrating down some steep rocks or even worse up them.
I posted my problem on another forum and this is the reply i got from a very well respected source. I have not tried this yet but apparently this is the thing to do, other than spending £200+ on an su.
If you look into the top of the carb, there should be a small brass pipe sticking upwards(the float bowl vent).This is the bit you need to extend upwards. You could always check the fuel height in the carb as well, theres usually a level plug to remove, or a specific measurement for float height, do you know the model type of thecarb?
Just a thought, you do still have the hot air feed from the exhaust manifold dont you? having to run with the choke on, and cuting out even on the flat may be carb icing.
Regards
Chris