Yes that knob adjust the idle. Turn it all the way CCW for high idle which is nice in the winter because you don't have to worry about keeping the engine speed up to keep it from dying. There is no other fuction associated with this knob other than adjusting the idle speed.

If you are having trouble starting then wait for a slow count to ten after the GP light goes out before you try starting. The relay keeps juice to the GPs for a while after the light goes out and after all of these years it isn't turning the light off at the right time.

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C