I've got an 86 Merc 170 (A560610) w/ Alpha One outdrive that starts, idles away from the dock, accelerates, gets up on plane, and cruises just fine for about 25-30 minutes. Then, while on plane, it will start missing--once every 2-3 seconds. It's barely noticeable at first, then over the next 5 mins or so, it gets progressively worse until it sputters to a halt. It will not restart right away. If I let it sit for about 20 mins, it will start right up and be fine (no missing, no sputtering) for another 15-20 mins. If I try to start it before the full 'resting period', it will only last a couple of minutes before the sputtering starts.
Things I've made note of:
--The temp rises to about 120F, and stays there the whole time until the 20min 'rest' period is complete, where it has fallen well below 100F
--I've replaced the carb fuel filter after several of the incidents with no effect, although the old filter always hads very fine rust or dirt particles in it.
--The last trip that this happened was after installing a cartridge-type fuel filter of unknown micron size. Perhaps I need a smaller micron filter?
--There is a stainless fuel line going from the pump to the carb that gets pretty warm. Could it be some kind of vapor lock problem?
--It seems that the cooling down period is what's (temporarily) fixing the problem, although the engine reaches operating temperature very quickly.
--If the problem is electrical, why would temperature affect it?
--Just noticed this past time that engaging the outdrive trim in either direction would cause an immediate worsening of the sputtering, but as soon as I stopped trimming (at any tilt angle), the engine would return to running as well as it was when I tried the trim. Could this additional electrical load be hurting the ignition? The batteries are maintaining their charge quite well...
I may try to run from a portable fuel tank with fresh fuel the next time I take it out. It's tough to troubleshoot since it takes 20min on plane for the symptoms to appear.
--Steve
Things I've made note of:
--The temp rises to about 120F, and stays there the whole time until the 20min 'rest' period is complete, where it has fallen well below 100F
--I've replaced the carb fuel filter after several of the incidents with no effect, although the old filter always hads very fine rust or dirt particles in it.
--The last trip that this happened was after installing a cartridge-type fuel filter of unknown micron size. Perhaps I need a smaller micron filter?
--There is a stainless fuel line going from the pump to the carb that gets pretty warm. Could it be some kind of vapor lock problem?
--It seems that the cooling down period is what's (temporarily) fixing the problem, although the engine reaches operating temperature very quickly.
--If the problem is electrical, why would temperature affect it?
--Just noticed this past time that engaging the outdrive trim in either direction would cause an immediate worsening of the sputtering, but as soon as I stopped trimming (at any tilt angle), the engine would return to running as well as it was when I tried the trim. Could this additional electrical load be hurting the ignition? The batteries are maintaining their charge quite well...
I may try to run from a portable fuel tank with fresh fuel the next time I take it out. It's tough to troubleshoot since it takes 20min on plane for the symptoms to appear.
--Steve
