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Earl or Bill, Maybe it would help to start with a simple way to set timing that will work with any old 4 cycle engine with a distributor (2 cycles like your weed wacker don't count here) using no test equipment, and that's more precise and easier to do than moving one gear tooth at a time. You just need to put in one brand new spark plug. The case of the distributor is usually held by a kind of collar to the engine block. If you loosen a bolt or two close to the block, the distributor case can move in a circle while the shaft with the rotor inside stays put. That's the easy way to change timing. Loosen those bolts without moving the distributor then start the engine and run it at idle then medium speed until it gets to normal temperature. Put your hand on the case (not the cap or wires) of the distributor and rotate it slowly left and right. You'll hear the engine speed up or slow down as a result of turning the distributor. Move the distributor until you get the fastest engine speed, then turn it back the other way a bit to be safe. You don't want to ignite the gas too soon or too late at any engine speed so you're trying to strike a kind of balance. The engine tells you by making more speed where it's happy -- as it's getting the best combustion from the same amount of gas at that "best" ignition setting. Next bolt down the distributor and get on. Ride around a little bit, accelerating the engine, or even pulling something. If you hear it pinging when it's under load - making a rattle kind of noise - then the plugs are probably firing too soon and you need to turn the distributor back a bit and try again. When there's no ping -- run it around a bit more then shut down the engine and pull out that new plug. If the plug is a kind of light brown -- you're in real good shape. If it has kind of white powder on it, you're running too hot, and need to back up the distributor a bit more. If it's black and sooty, you're not running too hot, but the carb is too rich -- wasting gas. There are all kinds of things you can tell by looking at plugs. Here's a link that will give you bunches of pictures of plugs and what they indicate about the way your engine is running. The timing adjustment has to assume you've done nothing else to the engine during this - so you have a good baseline. For example, no octane change in the gas, no wrenching on the carb that might cause an intake leak to make it run lean and hot, no changes in level or type of coolant, and so on. If you get too many things changing at once you end up not knowing where you are, and what made the results you're getting.
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