Got an 81 850G. It had obviously a rough and poorly maintained life, has 41K on the odometer. So, I worked on the wiring, which showed signs of having been overly hot. Cleaned connections, replaced some wires, added a Dyna S. Adjusted the valves, all are between .05-.08mm, none were zero clearance to begin with. Tires, brakes, all that stuff. I have put about 6K on it this summer. It took a while to get the carbs & airbox problems sorted, but run good it has. I made a 950 mile trip to Ohio, and last weekend I went to Wisconsin, 525 mile trip. On the way home the idle roughed up. Number 3 cylinder is dead at idle. Smooth as silk at speed. I have good fire, changed the plug out as well. Sprayed a touch of carb cleaner in #3 as it idled to see if the idle circuit got plugged on that carb, didn't make a difference. Played with the mixture screw for the hell of it, no help. The kicker is, that as it idles in 3 cylinders, there is an audible knock in the engine that cycles on and off every couple of seconds, very regularly. It is quite as a church mouse by the time it hits 2K on the tach. This doesn't register in my mind. I would think any mechanical problem would not disappear at RPMs. With the bucket & shim stuff, there is no rocker arm or adjustment to go haywire, a broken valve spring shouldn't work better at speed. There's not much in there to happen. A burned valve or sticky valve that doesn't close might kill the cylinder at very low speeds, but why the knock? This isn't sounding like a lifter tick, it's a knock that disappears totally off idle. I'm hoping one of you experienced GS guys can give me a hint before I tear it down. If it gets expensive I may look for an 1100G engine to stick in there.
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