Hi,
I have a 1988 Bayliner with a 5.0 liter OMC Cobra Sterndrive (GM engine).
A few weeks ago, the engine started stuttering badly at medium-high rpm when hot. When cold, everything runs fine for a few minutes. As soon as it hits operating temp (~170 F), it runs extremely rough when given any gas. If I go back to idle, it runs ok.
At the beginning of the season, I tuned it up, replaced plugs, points, condenser, rotor, distributor cap, and adjusted the dwell and timing to specs. The boat ran great all season until a few weeks ago.
Since this problem started, I replaced the carb with a rebuilt carb and replaced the thermostat (which was badly rusted and wouldn't move). I also re-adjusted the gap and timing to spec. None of these changes helped.
I tested the water pump by temporarily disconnecting the output hose - it pumps fine.
I checked the impeller in the outboard unit - it looks fine, though I'm not sure what constitutes bad.
The engine also runs fine, cold or hot, at all rpm's, when connected to a hose at home. I can rev the engine to 4500 rpm (in neutral) without any misses or stuttering.
Since it runs fine when cold, I doubt it is a fuel pump problem, a fuel intake problem, or a linkage-related problem.
The problem only occurs in open water, when hot, and when in gear above idle rpm.
I don't know what else to check or replace!
I'd greatly appreciate any ideas or advice to solve this problem.
Thanks, dave
I have a 1988 Bayliner with a 5.0 liter OMC Cobra Sterndrive (GM engine).
A few weeks ago, the engine started stuttering badly at medium-high rpm when hot. When cold, everything runs fine for a few minutes. As soon as it hits operating temp (~170 F), it runs extremely rough when given any gas. If I go back to idle, it runs ok.
At the beginning of the season, I tuned it up, replaced plugs, points, condenser, rotor, distributor cap, and adjusted the dwell and timing to specs. The boat ran great all season until a few weeks ago.
Since this problem started, I replaced the carb with a rebuilt carb and replaced the thermostat (which was badly rusted and wouldn't move). I also re-adjusted the gap and timing to spec. None of these changes helped.
I tested the water pump by temporarily disconnecting the output hose - it pumps fine.
I checked the impeller in the outboard unit - it looks fine, though I'm not sure what constitutes bad.
The engine also runs fine, cold or hot, at all rpm's, when connected to a hose at home. I can rev the engine to 4500 rpm (in neutral) without any misses or stuttering.
Since it runs fine when cold, I doubt it is a fuel pump problem, a fuel intake problem, or a linkage-related problem.
The problem only occurs in open water, when hot, and when in gear above idle rpm.
I don't know what else to check or replace!
I'd greatly appreciate any ideas or advice to solve this problem.
Thanks, dave