I have a 1985 Evinrude 175 hp outboard mounted on a 20' Grady White
Overnighter. I am having a problem with fuel delivery to the engine, let me
explain. The engine starts great and will run wide open at 4500 RPM for
about twenty-thirty minutes then it will bog down to 1500 RPM and I have to
leave it there or idling for a few minutes in order to continue. When the
engine bogs down I've noticed that my primer bulb goes completely flat,
sucked in on itself. When I let the engine idle the primer bulb slowly
fills with gasoline and becomes hard again. I can then put the engine back
at 4500 RPM again but this time I can only get five minutes before it bogs
down again, fuel starved. When the engine bogs down if I squeeze the bulb
frantically (It's still flat with just a little air in it) I can get fuel
through the line and get the engine to perform at a higher RPM, but I can't
squeeze fast enough to get it up to 4500 RPM. Again, if I put the engine in
idle, the vacuum in the bulb will slowly dissipate and it will return to its
bulb shape with fuel in it. My fuel mix is 50:1, I have new fuel, a new
water seperator, and a new clean fuel filter. I've disconnected the
anti-siphon valve on the fuel line, and I've checked and cleaned the fuel
vent and line. The primer bulb is installed in the correct orientation with
the arrow towards the engine. I do not know how old the primer bulb is as I
purchased the boat and motor this past spring. I have a spare engine and I
replaced the fuel pump on my engine with the pump from the spare. (Two fuel
pumps, same old problem). Does anyone have any idea what I should check
next? Can an old primer bulb cause these problems at high RPM's but not at
low RPMS? Could both fuel pumps be bad? Does a bad fuel pump deliver fuel
for twenty minutes and then malfunction, only to function again after
operating at a slower rate? Could the screen on the sender unit get clogged
and then unclogged given the parameters above? Could this be a carburator
or choke problem, are my floats sticking? The engine has been doing this
all summer, it's driving me nuts. When its running, it runs great, lots of
power, but then this fuel problem happens, over and over. There are fish
out there, any suggestions or ideas are appreciated immensely. Thanks