When my 6.2L Mercruiser port engine is cold it starts fine. Turn on the engine, wait about 5-10 seconds for the fuel pump to pressurize the system, and then hit the start button with the throttle at idle. It starts, idles and runs fine at all rpm's. When the engine is warm - has been shut down within the past couple of hours - it's hard to start, or may not start at all. I use the same technique as above, and the engine turns over and sounds like it's going to start, but when I let go of the start button the engine dies. I then try moving he throttle to various positions, and sometimes I can get it to start, and sometimes it wont. I had my mechanic install all new spark plugs, wiring harness and distributor cap. I still have the same problem. Any thoughts would be appreciated.