Hi I am new to boats and just bought a 1996 four winns horizon 190 with a 5.0 Volvo penta in it. I have recently taken it out to the lake a few times and it seems to struggle to start when leaving to go back to the ramp. Whenever I start the boat when it’s cold it generally starts pretty good only when it’s warm is when I have this problem. It will crank for a good 10-15 seconds and start very rough but slowly get back into regular engine noises. I’m not to sure what’s going on here any help would be greatly appreciated. On a side note I just took it to a mechanic and he told me he would have to take it out to the lake to diagnose and would have to charge me 300 to do that. Is this really something boat mechanics do or is the guy trying to rip me off?