if it's a Floater type carb, take the bowl off, Rinse out all the old gas with a little new, Also a thing to check is the hole though the bolt if there's one. I fixed a power washer from goodwill by cleaning out the jet in there, Runs like a champ now. A multitude of problems can be fixed just in the carb... as an after thought... did you check the gap on the plug? it might not make a huge difference... but I'd still check it to be sure.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed