superiormarine
New member
"Have I got a mystery for ever
"Have I got a mystery for everyone! I've got a 350 Mercruiser mag mpi motor here (2000 era) that is missing about 80 to 100HP. The motor has recently been rebuilt and runs great except for the lack of power.
Here is some history: Its in a 22' walkaround coupled to a bravo III drive that used to get 4600 rpm's. Last year it underwent surgery (complete rebuild) after losing the stbd manifold and ingesting water. It was rebuilt by a local motor service center, with a good rep might I add. Upon reinstallation and fine tuning everything seemed well until water trials, where the lack of power was discovered. Max rpm was 3700. The fuel system was drained and cleaned, new fuel pump and all new injectors and rails. New distributer cap also. Now rpm's are down to 3250. The engine has 6 hours on it now. Compression check shows 178 to 184psi +/-2. Spark plugs had not been gapped and varied from .022 to .010 but are now set at .045. Plugs showed no sign of fuel starvation.
Bottom line, the motor runs like a top. Starts right up, idles beautifully, revs smooth (in neutral). In gear idles great, doesnt stall spit or sputter, and increasing the throttle is smooth but lacks power. The boat barely planes anymore and struggles just to get 3200rpms. Advancing and retarding the timing (mechanically) has some negative effect (expected). This boat is trailer kept so has no bottom growth.
I can't figure out why a motor that runs so well could have such a major malfunction unless it has the wrong heads or cams. The rebuilder denies any rebuild problems and backs the engine against mechanical failure but insists that the problem is with the computer or fuel. ANY IDEAS?!?!?"
"Have I got a mystery for everyone! I've got a 350 Mercruiser mag mpi motor here (2000 era) that is missing about 80 to 100HP. The motor has recently been rebuilt and runs great except for the lack of power.
Here is some history: Its in a 22' walkaround coupled to a bravo III drive that used to get 4600 rpm's. Last year it underwent surgery (complete rebuild) after losing the stbd manifold and ingesting water. It was rebuilt by a local motor service center, with a good rep might I add. Upon reinstallation and fine tuning everything seemed well until water trials, where the lack of power was discovered. Max rpm was 3700. The fuel system was drained and cleaned, new fuel pump and all new injectors and rails. New distributer cap also. Now rpm's are down to 3250. The engine has 6 hours on it now. Compression check shows 178 to 184psi +/-2. Spark plugs had not been gapped and varied from .022 to .010 but are now set at .045. Plugs showed no sign of fuel starvation.
Bottom line, the motor runs like a top. Starts right up, idles beautifully, revs smooth (in neutral). In gear idles great, doesnt stall spit or sputter, and increasing the throttle is smooth but lacks power. The boat barely planes anymore and struggles just to get 3200rpms. Advancing and retarding the timing (mechanically) has some negative effect (expected). This boat is trailer kept so has no bottom growth.
I can't figure out why a motor that runs so well could have such a major malfunction unless it has the wrong heads or cams. The rebuilder denies any rebuild problems and backs the engine against mechanical failure but insists that the problem is with the computer or fuel. ANY IDEAS?!?!?"