I'm a newbie and love this forum!!<br /><br />I have a 30HP Merc outboard 1999 4-stroke, sn:OG907873, mod: 1-F30312VD. It is hesitating during acceleration and occasionally stalls if I try to push the throttle to get it over the "hump" to where it will continue to run.<br />As a mechanical engineer I just had to try to diagnose the problem myself and here is what I learned. I suspect the accelerator pump.<br />I took off the air intake manifold and watched as I accelerated. The bottom two carbs are shooting fuel into the butterfly but the top jet is not "tipping in" the fuel. The accelerator pump plunger and bellows on the top carb travels fastest to its end-stop which makes me think that the plunger is the culprit. Also, when I take off the top plate and rubber diaphragm and spray into the holes, the jet discharges the spray?? Any thoughts?