Vapor lock?

[tonyjh63]

Ok, went to the lake yesterday...cruising along at about 3000 - 3200 rpm when the the rpm started dropping, engine losing power. Got all the way down to idle, but never died out completely. Shut the engine off, cracked right back up, started off, same thing - started bogging down at cruise. Limped (about 2000 rpm) our way to a restaurant to eat. Came back out an hour or so later, boat ran at 3000-3200 rpm all the way back to the dock, no issues. Engine is a 4.3 Mercruiser w/carb. No fuel/water separator/filter, and yes, then is some ethanol gas in the tank...
Would this be vapor lock? Maybe air getting into the fuel lines somewhere? Thanks in advance!

 

[Scott Danforth]

check your fuel vent line

 

[alldodge]

No VL with a carb, probably tank vent line is clogged like Scott mentioned. When it bogs down, stop, shut motor off, then open gas cap and listen for air being sucked in.

 

[tonyjh63]

No VL with a carb, probably tank vent line is clogged like Scott mentioned. When it bogs down, stop, shut motor off, then open gas cap and listen for air being sucked in.

Really, no vl with a carb? I thought it was specifically carb boat motors that occasionally suffered from vl, and that the problem was eliminated with fuel injection engines (something about the fuel system being under too much pressure for vl to happen)?
Thanks for the advice about the gas cap - will try it next time!
Tony

 

[tonyjh63]

Hey, reading up on this tank vent line thing reminds me of something regarding my boat...sometimes, when I put gas in her, I'll get a real strong smell of gas in the boat. When this happens, I open up the bow seats (my gas tank is up front, with the filler on the starboard side - that's where Bryant puts their gas tanks/fillers) to see if there is any gas spillage, but can never find exactly where the smell is coming from. Could this be related to my problem? Thanks!
Tony

 

[alldodge]

Other way around, no VL issue until EFI came along.

If you have a clogged vent and a loose connection on a hose then more fumes. Check your fill hoses, if you have an old boat (before E10 gas) then may have issues with fill and vent hoses. If newer, spiders or other critters might try and build a next in the vent hose

 

[scoflaw]

VL in carbed cars is certainly a reality. Thus the invention of the phenolic carb spacer to stop heat transfer.

 

[Scott Danforth]

while vapor lock can happen with a carbureted motor, the symptoms are generally one of two conditions.

a no-start after a short period with the motor off (usually when warm). this clears itself after the engine cools down
a start followed by a stall within about a minute (as the fuel is used from the bowl), followed by a non-start as the fuel is prevented from entering the carb

what the OP describes is more like a plugged vent line and the fuel pump is trying like 'ell to suck the sides of the tank in to get fuel. fuel flow is diminished and the motor struggles to make power at any RPM, however can usually run and idle

another likely scenario is the fuel has moisture in it and the motor is running like crap on a mix of water and fuel. it would run rough, not make much power, etc. this case the motor may die at idle

 

[alldodge]

Never seen a carb VL on a boat, is some issue on a car because temps are much higher. If all the fuel boils out the bowl, more cranking will refill the bowl, but this IMO is not locked, just carb dry