Can anyone give me some advice on my Mantis please ?
The problem is that the machine starts OK , runs up to certain revs , then cuts out if revs are increased , it will start again straight away though, mystery !
So when you add throttle it chokes off? That throttle runs an air vane or second venturi choke plate as I recall. So you are adding air and it chokes off due to lack of fuel? You are trying to increase vacuum which should draw fuel via suction but no fuel comes on the high circuit. Or the vacuum level is failing at high rpm. Vacuum seal failure means a gasket kit/fuel line check and lack of fuel means clean the carb jets. An old fuel filter/pickup line could be collapsing under vaccum. The reverse can easily be true, that a air return line is not returning air to the fuel tank properly because of a bad tank seal which disallows draw on throttle up but allows idle and low-mid range vacuum pressures.