Remember you are applying the special gauge to the rounded top of the fuel needle, not the lever itself, so the shape of the fork on the lever is not critical, except that the needle should be supported by both sides of the fork.
Post-edit: The above instruction is wrong, the gauge is applied to the opposite end of the metering lever, directly above the spring. My error. I must be getting too old for this stuff, it isn't long since I last adjusted one of these.
In principle you can adjust the fork either by holding it and bending it in place, or by taking it out. I prefer to take it out, because it is rather springy (it is not dead soft steel) and I do not like to risk having the tip of the needle pushed hard against its seat. If you take the lever out to adjust it, you can be quite careful to bend both sides of the fork evenly. On the downside, putting the lever back in without the spring going ping and disappearing, requires care.
Once the metering lever height is set, adjusting the mixture is theoretically easy but can be rather frustrating in practice. You do it like this. If the carburetor has been stripped completely, you simply reinstall the H and L needles by screwing them all the way in until they very lightly bottom. Then you turn them both anti-clockwise one and a quarter turns. That gives you fuel settings that will allow the engine to start and run, though probably not especially well. Then you set the idle speed screw fairly high, start the engine using the standard procedure, and let it warm up. Once it is warm you reduce the idle speed as low as you dare, or ideally, until the clutch disengages and the cutting head stops rotating. Then turn the L screw (idle mixture) slightly clockwise a bit at a time until the engine suddenly runs smoothly (that is, 2 stroking - it will have been 4 stroking initially). Move the needle clockwise and anticlockwise until you find the most anticlockwise position that allows it to 2 stroke, or just a bit richer (more anticlockwise) than that.
Next step is the H screw (high speed mixture). Open the throttle wide and turn the H screw clockwise until it suddenly smooths out and 2 strokes. Feel around to find the most anticlockwise position (that is, richest mixture) that allows it to two stroke fairly steadily. However do not dally on the clockwise (lean) side of the best position, where it stops 2 stroking and starts 4 stroking. Lean mixture at full throttle can damage the engine. (This is especially true of high performance chainsaw engines, but you should always avoid running on the lean side at high speed/heavy throttle, for any engine, 2 stroke or 4 stroke.)
That is the official tuning procedure. In practice, you may find that when you have done that, there is a lean zone somewhere between idle and the "starting" throttle position. Consequently if you open the throttle suddenly from idle, or if you linger for a while anywhere below the starting throttle position, the engine may hesitate or stall. If that happens it is best to make the L screw just slightly richer than the 2 stroking position, to overcome the problem.
Last edited by grumpy; 06/02/14 12:26 AM. Reason: Add Post-edit
