I have not used my chipper/vac for a couple of years as it had become really difficult to start & I would get fustrated. This is a 5hp model with a Tecumseh engine. I had another go today. Checked fuel initially and was surprised to see the tank completely empty. Filled it partly up and then noticed the air filter/cleaner unit was dripping with petrol. Took this apart and the petrol kept on flowing out. I suspect the air filter probably needs changing but I just oiled the pre-filter. Low and behold it started but just as I was about to jump round with joy it stopped and that was that. The air filter continued to drip/flood with petrol so I have given up for now.
If anyone can help identify the potential cause this would be appreciated. I will admit it hasn't had a proper service apart from oil...

Simple. The fuel valve in the carb is stuck because you don't use fuel stabilizer like Sta-bil.

Sometimes a VERY small amount of seafoam carb cleaner will work in the fuel tank (no gas). This may free the fuel valve after a few pulls/waits. Use the proper mix of seafoam and gas and run it for a while until the engine stops.

Otherwise carb has to come off and cleaned.