Mercruiser 3.0 140 loosing umph as the day goes on????

[Planodave]

1986 Mercruiser 3.0 140 hp starts the day off in good shape, however as the day goes on it seems to loose RPM and power. Was wondering if it was a heating issue but does not seem to ever get above 160-170 and thought if it was loosing compression, but would that happen if it was getting hot? (thought things would expand and get tighter if getting hot. Son thinks it is the fuel pump. Any ideas or suggestions appreciated.
Thanks in advance
Dave

 

[Planodave]

Mercruiser 3.0 140 looses umph at the end of the day

1986 Mercruiser 3.0, 140hp starts the day off in good shape, however has the day goes on it seems to loose RPM and power. Was wondering if it was a heating issue but does not seem to get above 160-170 and thought if it was loosing compressio, but that would not happen if it was getting hot?? (Thought things would expand if getting hotter)? Son thinks it might be the fuel pump. Any ideas or suggestions are appreciated.
Thanks in advance
Dave

 

[72 Chesapeake]

My boat has been acting similar lately, mercruiser 165 seems to start missing and lose power after hot and been running a while and then idles good. Seems to act erratic but has done this a couple times. I'm thinking possible plugged carb jet or moisture in gas, going to put some heet additive in gas and see if it gets better. Just went through new cylinder head and valve issues couple years back so don't think that's my concern. Just an idea if you haven't already checked

 

[alldodge]

Could be a few things, has the points and condenser been changed?
Have you tried removing the gas cap when it starts slowing and listen for air being sucked in?
Fuel pump maybe getting weak, antisiphon valve, fuel filter

 

[Planodave]

Thank you both for the suggestions