Mercury 40 fuel problem

[swill936]

I have a 1998 Mercury 40 (2 stroke) elpto with a confounding fuel issue. When running above half throttle, the bulb will go flat and cause the engine to starve for fuel. I have rebuilt the fuel pump twice. nothing out of the ordinary noted on the pump body. The fuel line from the tank to the engine is also new, bulb and connector included. The on-engine filter has been replaced and I added an inline filter.

The engine is on a Key West 1500cc and the poly tank does not allow access to the pickup to check any in-tank filtration for plugging. The previous owner removed the oil injection and I mix the fuel in the main tank. The engine runs like new otherwise. Starts, idles and runs great.
I'm at my witts end to solve this. I have had the engine for several years and this has been a recurring issue...regardless of what the local shops or I do.

Any suggestions would be welcome!!

 

[racerone]

When the bulb collapses the fuel pump is working just fine.-----The issue is from the bulb to the tank.----So check vent of fuel tank.----Anti-syphon valve ( if equipped ) and the screen inside your fuel tank.-----A simple test would be to run with a seperate 5 gallon tank.----Should be easy to solve in my opinion !

 

[airshot]

Yes, try another tank, sounds like the pickup in your tank might be an issue...

 

[QBhoy]

You have a restriction somewhere before your primer bulb. Could be the pick up in tank…a check valve after it…or quite common to find your primer bulb is the wrong way round.
The fuel tank vent could be blocked too.