My fuel line bulbs on my twin mercury engines collapse (suck inward) whenever i try to go fast, why is this?

Question

the boat has not been used in two years. it is a 1993 robalo with twin engines same year 200 hp each. they are two cycle engines. they start and run great. but when i am going slow. the moment i give it all she's got the right engine glass filter runs out of gas. soon after that the fuel line bulb collapses. if i continue to give it all she's got then the left engine does the exact same thing and they both die out.(shut down, turn off). i did have water in the tank but that has been taken care of. i have also replaced the fuel lines starting from the engines to the gas water separator. i have also replaced the fuel line bulbs and the glass filters. i have cleaned the filter screens that are in the hose that runs into the gas tank. the gas tank holds 177 gallons. i have 70 to 75 gallons in it now. i have not bought a new gas water separator though. i see alot of build up on the outside of the boat in the escapes by the gas fill. do you think that is the problem?

Answer 1

Sounds like you have a blocked vent.

Answer 2

Bulb collapsing can only be caused by a restriction upstream of the bulb, faulty bulb, or blocked vent.

The fuel pump is sucking hard but no fuel can get through, is the reason for the bulb to collapse.

Highly recommend rebuilding the carbs on these engines, after 2 years of inactivity they are sure to have some varnish left behind by evaporating pre-mixed oil/gas.

Also recommend replacing water pump impellers, routine operation but failure has disastrous consequenses.  They will take on a set and be less effective, may have begun to dry rot, you don't want a piece of neoprene rubber blocking your water jacket.

Answer 3

the vent is stopping up on it,try cleaning it,i have seen this happen a few times,other than that with new bulbs on it you shouldn't be having any problems from it,my vents stopped up on my boat and it would almost close the line up on it and the engine would have to about die before they would open back up,good luck with it.

Answer 4

Take the gas cap lose and try running the boat if dosen't works the screen on the pickup is plugged> If it works it's the vent or hose to the vent> Check the shut off valves for blockage>

Answer 5

Have you checked your anti-syphon valves coming from your fuel tank?If there is anything stuck in there that could cause your problem,but I would bet the diaphragms in your fuel pumps need to be replaced.This is the major cause of a collapsed fuel bulb.I am sure that after sitting for two years,

they have dried-up and are no good.Because the boat has been sitting for so long the vents on the fuel tanks could be plugged also.

Answer 6

You cleaned the pick up tube in the tank, most, not all, tanks have a one-way valve at the outlet on the tank. It will get stuck, it has a spring &  a ball in it. You can replace it or just knock the ball & spring out of it. (remove it of course)

looks like this::

http://shop.easternmarine.com/index.cfm?...

The tank vent could be stopped up. It being a 1993, the main fuel line from the tank to the motor(s) could be collasping on the inside.  I have a 1997 Wellcraft CC that I am going to replace the main line this winter. Also, are the bulbs good & hard ? I have seen some blue ones that are real soft & will coIlaspe. Make sure the fuel lines and main filter/seperator is large enough to feed twins.