Will not run on fuel lines (1999 Yamaha 5hp 2 Stroke)

I have recently bought a boat which came with a 1999 Yamaha 5hp 2 Stroke outboard and when I connect the fuel line from the auxiliary tank it kills the engine.

The strange thing is it appears not to be starving the engine of fuel but flooding it instead. I can start the engine and it runs fine on the residual fuel until I connect the fuel lines then within a few seconds the engine stalls.

The reason why I think it is flooding the engine is because after connecting the fuel lines it takes many pulls of the starter cord before the engine starts again, once started it runs on the residual fuel until it runs out or the fuel hose is connected again.

The engine seems in very good condition and runs well otherwise.

need to check the carb float, and also check and see if you have a hole in the fuel pump Diaphragm.

Thank you for your reply.

I will check these, is there one which you would check first being the most likely candidate?

check the float first and then the fuel pump.

Thanks Coueytwo,

Having chatted with my uncle who is technically minded and your advice on the float I ran an engine cleaning product through it and after a while it was able to run of the fuel lines without any problems. It seems like the float may have been gummed up.