I have some problems with our old and trusty HR 21. I do not want to give it up, despite it's age !
Trouble is that it uses to develop a lot of coal on the spark plug, and then it dies after a while.
I have taken the head of, checked the valves and they look fine to me.
I have cleaned and checked the carburettor, and it looks clean and nice to me.
What puzzles me is "how to adjust the carb". Is there a manual other / better than the green Honda service book I bought on ebay ? It does not really describe how to fine -tune it. It does not really react on the rear small setscrew (with the spring under it, the "idle screw").
When I manage to get it to run (on a fresh new BP ... 6 NGK plug), then it does a sagging noise- revs up and down, up and down, it changes every second. Wrrrr,wwwwwrrrrr, wwwrrrrr. Like a saw.
What can I try next ? I tried new fuel.
And I tried a Colourtune glass spark plug (I have a lot of old car experience so I thought it might work here, too), but this was fouled / covered thick in black deposits within a few seconds so it stopped running !
So: Why is it running so rich, what can I do ?
Many thanks for any help !