Mercruiser 502 MAG MPI Hard to start when warm

" The motor starts fine when c

" The motor starts fine when cold even after sitting for a month or so. When the motor is up to temperature and is shut down for more than a few minutes the motor won't fire unless full throttle is given to it in Neutral. One Mercruiser tech said it was possibly vapor lock and I noticed Mercury has a tech bulletin noting this situation. Following their instructions to prevent this case - i.e. opening the hatch while idling into a cove to allow air to circulate in the engine compartment - doesn't help. The motor when new never had this problem. This started a couple of years ago. Also, at times there's a little bit of a fuel smell when opening the hatch. We and our service people can find no leaks anywhere.

Any ideas? "

" If this is a Fuel injected e

" If this is a Fuel injected engine I don't think vapor lock is a possible issue. It sounds like from your description that it is flooded with too much fuel after shutdown and restart, but thats really not possible with fuel injection unless a sensor has gone bad. Have you replaced the spark plugs since it was new? Try running the boat for awhile to get it to normal hot temp, then shut down for 10 min and pull a spark plug to check if its normal brown/tan or loaded with fuel, it should not smell alot like gas or be wet with gas. "

I have a 1998 5.7L 350 MAG fue

I have a 1998 5.7L 350 MAG fuel injected direct drive inboard ski boat. My engine had these same symptoms. If it sat for a few minutes while waiting for a skier to gear up it would start hard. If it did start would run rich and then stall on take off. My solution was a bad check valve on the cold water side of the shower system. The valve would let the block water drain back into the lake. Cold water in the hot motor raised hell with the ECM. Does your temperature guage fluctuate on start up?

"your problem is the fuel pres

"your problem is the fuel pressure regulator. once warm the regulator diaphram which is ruptured is leaking raw fuel into the vacuum line causing the engine to flood, thats why you need wot to start engine. replace the fuel pressure regulator and your problems are gone. to verify remove the vacuum line to the fuel pressure regulator and you will find raw fuel, which there should be absolutely none."