Hi.
Only reason I’m thinking about the fuel pick up is that I’ve had this on two different boats.
Both boats I got fairly cheap after they were sitting unused for a number of years. One of them I am ashamed to admit, I was filling with fuel from cars that had been scrapped so fuel was of doubtful quality. Turns out on both occasions the fuel pick up pipe was being blocked by debree. She would idle fine bit when you increase the fuel demand the more suction there was at the tank. The more crap got sucked against the pick up pipe and the gauze it had over it. Hence the blockage.
One of the boats, I totally cleaned out the tank by sucking all the crap out it through the fuel sender unit hole. The other, I ashamed to say (was only a boy), I just raised the pick up pipe an inch or two further off the bottom of the tank !
worth a look.