primer bulb

my 1999 75 hp merc runs great except when i go below 2000 rpms for an extended time. after about 10 minutes the primer bulb goes flat...this happens all day long if running slow. how do i fix it?

Re: primer bulb

Either there is a screen on the fuel pickup in the tank that is plugged, the tank vent is not working or the anti syphion valve on the fuel outlet is sticking

Re: primer bulb

thanks..if these are the problem why does it not happen above 3500 rpms when cruising...beautiful lakes up there...have a friend on bellaire.

Re: primer bulb

Perhaps something in the tank floats over the pickup at slower speed. When you say the bulb goes flat do you mean it just gets soft, or does it really flatten out? There is a difference. A primer bulb does not stay firm when the engine is running.

Re: primer bulb

golfes, I guess I read your thread backwards, sorry, but the antisyphion valve could still not be opening well at slow speeds causing aproblem and as fuel volume increases opening

Re: primer bulb

Listen to Laddies, and try a new bulb, mercury if possible, the others are not good quality. My old bulb/ clamps had leaks and the valve was weak, and like yours ran good above 2000rpm but sputtered at low rpm.<br />Use merc not wallyworld, I tried both the cheap bulb would not get firm.

Re: primer bulb

wow! thanks for all the help...what really happens is that the engine starts to run rough and then quits...the bulb is then soft and you have to pump it to start the engine...however, when you hear the engine start to sputter if someone gets to the back and pumps the bulb before the engine stalls all is ok for awhile, but just gunning it when it sputters doesn't help. I will change bulbs and check for air leaks.

Re: primer bulb

That sounds like a fuel pump problem...

Re: primer bulb

Can be sucing air on the vacuum side (Between 1st fuel pump and tank). And the fuel pumps can keep the fuel flowing better at higher rpm.<br /><br />If you checked your vacuum side, and you're confident that all is well, new diaphrams and non-returns in your fuel pumps will sort you out.<br /><br />Note: To help eliminate the vacuum side. When the bulb goes soft and motor starts to stutter. Pump the bulb as you do now, but take note of how easily it expands again after each pump. If it battles to expand, it means something is resticting the suction side. Shake the tank up a bit and see if it helps.<br /><br />Else it's either an air leak, or worn fuel pumps. Replace diaphrams only. If the situation doesn't improve, go for the non-returns.<br /><br />Else, fit a low pressure (0.3 bar) electric diaphram fuel pump. SU pump as they used to be called.

Re: primer bulb

Originally posted by rickdb1boat:<br /> That sounds like a fuel pump problem...

Click to expand...

I would agree.The square fuel pumps on those outboards are not really strong at an idle speed.I believe there was a service bulletin stating that the rubber check valves that were sent with the fuel pumps would be affected by the additives in the fuel and curl.The replacement check valves are made out of plastic.