mercury fuel issues 86' 150

[17rogue70]

boat has sat for about 6 mo. replaced the stator and lake tested yesterday , all was well until I went on up to the higher rpm range. about 45 sec into the run , the rpms dropped down to around 3000+/-. I squeezed the primer ball and it was firm. pulled the rpms down to an idle and precede to take off again . 3000 to 3400 all is good , run into the upper 4000 rpm range and about 40 45 sec later the rpms start to fall off again. checked all fuel lines and fittings and found one bad clamp that was loose between the fuel pump and inline fuel filter. changed out the fuel water seperater, checked the main jets and they are clean as a whistle. no water in the system as I have drain and replaced with fresh fuel and oil. could there be something else I am missing along the way. starts fine and idles fine. last time the boat was run, it ran fine until the stator crapped out.

 

[Chris1956]

Re: mercury fuel issues 86' 150

Sure, check the antisiphon valve in the fuel tank pickup. Maybe it is restricted. Second culprit is fuel pump. Third is fuel line size. It should be 3/8" ID fuel line.

 

[CharlieB]

Re: mercury fuel issues 86' 150

Unplug/disconnect the two yellow wires connecting the stator to the voltage rectifier, retest operation. If this cures the lose of power then replace the rectifier.

Test fuel pump output cranking. Pull the spark plugs to save wear and tear on the starter and battery. Pull the lanyard to kill the ignition. Disconnect the fuel hose at the carbs, point it into a suitable container like a plastic coffee can, crank the motor for one minute. Fuel flow should remain a strong pulsed flow.

How old is the fuel hoses? The clear lining of some hose degrades from alcohol in the fuel, the lining can slough off clogging fittings or carbs. The lining can tear a 'flap' that can fall over and restrict fuel flow. Consider the age and condition of all fuel hose, possibly replace all hoses.

 

[17rogue70]

Re: mercury fuel issues 86' 150

Chris there is no antisiphon valve , fuel pump was rebuilt before this issue came about and the fuel line is right about 1 yr old . thank you sir .

Charlie, you mention the rectifier. how would this affect the fuel ? excuse my ignorance. I will test when I am around the boat again tomm afternoon. as well as the fuel pump pulse flow. fuel line is 3/8 and right at 1 yr old. these are test I will perform when I get home from work tomm after noon. thank you for the info and and possibilities. will post the results after completed.


thank you both so very much, mike in Orlando fla

 

[CharlieB]

Re: mercury fuel issues 86' 150

The fact that you squeezed the primer and it remained firm may be a clue.

You may still have a bad fuel line after the fuel pump restricting flow to the carbs, it may be that it takes that 45 seconds or so for the carbs to run low on fuel, passing only enough fuel to maintain that reduced RPM,

OR,

The ignition system is reducing voltage and only making enough spark to support running at that reduced RPM.

A failing rectifier can cause strange EMF within the stator and reduce voltage generation within the high speed windings, thus reducing RPM. Disconnecting the rectifier and retesting operation is a quick and easy test. If the motor picks up and performs correctly, replace the rectifier. Done.

The fuel pump flow test may need to be repeated one each carb feed hose as reduced flow to even one carb will reduce power and drop RPM under load.

Between the two test you should narrow your search or even identify and cure the problem.