Re: Motor Noise 2000 90hp Merc
Hi Fastmetal<br />I also have a 2000 90hp 2 stroke Mercury that had exactly the same noise, it was mainly noticeable between idle speed and 2000 rpm. Motor checks out ok plugs look normal, strong water flow at telltale 5psi at idle 12psi at WOT on water pressure gauge, thermostat ok no overheating, motor performance good.<br /><br />as you said it only happens after long runs, gone completely on restart,or running in test tank, dealer checked out during first scheduled servicing (20hrs) said they could not detect noise, I decided to troubleshoot myself, I remembered hearing similar noises on leaking inlet & exhaust manifolds on vehicles and suspected a possible air leak in fuel line.<br /><br />Found these problems <br /># primer bulb never got real firm, bulb had been installed in fuel line between filter/water separator unit and motor and was not priming properly because of air in filter.<br />#appeared to have a very small air leak between underfloor tanks and filter, this allowed air to slowly enter filter till fuel level in glass bowl dropped to be almost level with central fuel outlet in filter allowing some air to be sucked into carbs when motor was at lower rpm and lower fuel pump vacuum, at higher rpm the fuel pump operating at higher vacuum was able to suck fuel through without problems. <br /><br />Installed another primer bulb (used merc parts)before filter, drilled an airbleed hole through a suitable boss on top of filter and tapped thread and inserted an airbleed bolt to boss, now I can pump fuel into filter unit after filter change and bleed excess air from bleed screw on filter, replaced faulty fuel line clamp on entry line to filter. Primer bulb near motor now pumps up hard, no air bubbles in filter and with 3 long runs at 3/4 throttle (30 miles each)since this work, the noise has disappeared.<br /><br />This may not be your problem but it could be worth looking for possible air leaks between fuel pump and fuel tank or filter.
