Hi, I've had a similar problem with my HP414. After a couple of pushes on the priming button, it started straight away, ran for about five seconds then stopped. I'd tried all sorts, new carb, fuel line, filter, but it was still the same. I've now found out what the cause was and feel a bit silly, it was all down to lack of good workshop practice! I found that there must have been an air leak between the engine port and the large plastic spacer before the carb. When I took this off I thought the mating surfaces and gasket looked a bit poor so I completely cleaned them both and fitted a new gasket with a sparing amount of gasket sealant. As soon as I started it the difference was amazing, it now runs perfectly. Just shows, when I fitted the new carb I obviously should have done this anyway!