5.7 H.O. Merc Hard Start After Running

[dillonboat]

I searched the Forum but only found this issue with fuel injected 5.7s. We have a 97 Signature 190 with the 5.7 H.O. carbureted engine. Up till recently she's started completely without issue. Hot or cold. Last two trips we've had problems once out on the water trying to get her to start after shutting her down or she might stall if we try to run her at idle after cruising for a while. We have a lot of manatee zones here so winding her down after 15 minutes at 2500+ rpm is common. If I switch into neutral she might stall upon re-engaging the drive either in forward or reverse. If we sit for five minutes the engine will fire back up no problem but that's a dangerous situation if we're at the ramp or the tide is ripping in or out. She doesn't seem to idle rough and will cruise forever without so much as a skip. I assume this is a fuel issue rather than spark. Before I start pulling crap apart or pull her down to the mechanic does anyone have any starting points? It seems to be heat related or at least that's the tip of the issue. Now next time if she takes multiple tries straight from the dock then I have to rule out heat. Maybe blast some cleaner down the carb? Change the fuel filter? Seems like it should be simple. Thanks in advance.

 

[BillK2632]

I would check a few things things first:

1. Fuel filter - pull it off and pour it in a glass jar to check for debris and replace it.
2. Carburetor inlet filter - check it, but by the time you pull it out might as well replace it.
3. Fuel line / anti siphon valve. At the age of your boat, the fuel line could be deteriorating especially if using ethanol fuel. This usually happens from the inside, so outside the line looks fine. Anti-siphon valve is a check valve, with a spring ball in it, over time they corrode and don't work smoothly anymore - can create a no fuel condition. If you suspect either, just replace them, cheap and on your boat should be easy.
4. Fuel vent line - make sure it is clear. One check is next time this happens, take the fuel cap off - if you hear a vacuum and then things work, that was your problem.

When the boat stalls and finally restarts, does it smoke like a rich fuel situation? Need to determine if it is flooding and stalling or starving for fuel and stalling. If flooding, I would still do the above, but then start looking at the carburetor. If it's a 97 it could be due for a carburetor rebuild or good cleaning - float sticking etc.

FYI, a few years back I started having similar problems with my boat (1999 185), stalling, hard to restart etc. I ended up doing all of the above - my fuel line was the ultimate culprit, it was deteriorated and collapsing under a load causing stalling, plus little pieces of it were making their way into the fuel filters and even the carburetor. Also, age and ethanol fuel had taken their toll on the fuel lines.

Another possibility is vapor lock. However vapor lock usually occurrs after a hot engine is shut down and try to restart within 30-45min. Fuel has vaporized in hot fuel line and engine won't start. Ok after it cools down. Vapor lock doesn't usually cause a running engine to stall.