Small 3.5hp on a 46cm cut lawn mower. Engine runs slowly and is visibly burning lots of oil and sooting up a brand new spark plug within one minute. I can make it run faster by manually pulling on throttle spring near carb but have no idea how to adjust. Have used clean petrol so fear a gasket maybe ?
On initial start up runs "normal" for about 10 seconds before slowing right down.

Phil&Ollie, September 2009

Phil,
Top Notch. I changed diaphragm between tank and carb (£1.80 +vat ) and just as you said - twenty minutes later it is running as normal. Thank you very much indeed.

John,
also thanks again to you as the air filter did need a good clean out.

Regards,

Phil

Phil & Ollie, September 2009

Replace the carb diaphragm between the carb and tank. Costs about £2, and takes 20 mins to fit.

phil_saunders(a)bigfoot.com

Phil Saunders, September 2009

John, Many thanks. Have taken the filter out and give it a good clean and have even tried running it with filter completely removed. Smoke is very definitely not blue but a real sooty black.

Phil&Ollie, September 2009

First of all, check that the air cleaner element is clean. If its dirty, the engine will chuff black smoke and soot up the plug. If the smoke yours is making is blue, then it is burning oil and needs attention.

John, September 2009