Ben, a lot of these saws have a plastic protective cover over the H & L screws to stop accidental tampering when things start running rough. The machine is factory set with the correct petrol/oil ratios, IF your mixture is not at the same ratio ie; to much petrol, over a period of tank fillings the neater petrol will flush some of the residual oils out of the crank and the saw will start running-on. To much oil, and a build up of oil in the crank will cause smoking and carbon to build up on piston/head, plug and exaust which leads to choking the combustion and exaust system. Your question, if plastic protection is inplace, remove and that will allow access to the adjustment screws. Gently turn both H & L screws fully in, then approx 1 turn out. Turn throttle screw fully in and leave. Try starting the engine to run (WITH CAUTION DUE TO THROTTLE), when and if running slowly turn L screw in until the engine starts to splutter and then turn back out to splutter. THE L setting is 1/2 way between the two approx. Turn throttle screw back out to reduce revs of saw. The hard bit is the H screw, this needs tweaking when you rev the saw up (either in or out) so that the saw picks up witout faultering and also might need a fine tweak on the L screw to achieve this.
NB> If your petrol/oil is to lean, the piston and barrel will over heat resulting in a 'scored' skip job. To rich in oil a build up of carbon deposits can also cause serious damage by flakes of carbon braking away and scoring the piston and barrel, not to mention the effect of the exaust smoke upon yourself. Hope this has not confused you!
Martyn
July 2006
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