My SDL is running rough at idle sometimes with a slight knocking sound. I suspect it may be incomplete combustion or bad spray pattern. It always runs smooth during the 'after-glow' period ( I installed the 'after-glow' circuit with info from this forum ) then it runs rough sometimes until the engine is hot. I just want to do a test to turn on the glow plugs while it is running rough to see what difference does it make. It would only be a temporary test.

Any simple method?

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300SDL project car