The engine can surge as a result of both lean and rich mixtures. If it's rich, it will be making lots of black smoke. If there is no smoke, it's lean.
Chances are that if you had to clean out the carb, it's still partially blocked. Depending on date, there may be two mixture screws (main - under the carb bowl, and idle - recessed in the side of the carb), or just one (idle only), or none at all.
Start with both screws 1 1/2 turns out from fully in.
If there is a main jet adjust, set control to 'FAST', then screw the needle in and out 1/4 turn at a time, and observe the effect. As the needle is screwed in, there will be a point at which the engine won't run at all. Same with screwing out. The correct position is half way between these 2 extremes.
Set control to 'SLOW', and repeat with the idle adjust.
The two are inter-dependant to some extent, so re-check the main after you do the idle.
If there is no main adjust, remove the bowl nut and ensure that the jet hole that may be (depending on model) in the side of it is not blocked. It's easy to miss!. Then djust the idle as above.
Advise if you need more helo.
phil_saunders(a)bigfot.com
Phil Saunders, November 2009
