A few weeks ago I inherited one of these mowers. It was running fine, with excellent low-speed tickover and smooth running under load. It is now reluctant to idle, with the governer constantly cutting in and out, resulting in "hunting", and stalling if the throttle is set at the tick-over position. The spark plug is sooting up, indicating rich running, but there is no mixture control on the carb. The fuel has been changed for fresh, but the problem persists. The plug is fairly new and has been re-gapped at approx 15/20/ thou. Various settings have been tried but with no difference.

Any ideas please?

GMC, August 2011

Carb needs cleaning. There is no fuel filter fitted as standard on the Classic thus anything going in the tank will go to the carb. The injector hole is tiny within them. Depending on your model you may have a Delorto or a Tecumseh carb. The bowl will just need a rinse but you should use a small splinter of wood to clean out the fuel jet. Don't use anything else as this will alter the jet, it's delicate.
You may already know this so I apologise if so.
I have taken apart both types of carbs to clean on several models. It's amazing what a difference it makes.

MowerMan, August 2011