b87 MIE 260 2900 Max RPM WOT

"I have a Sea Ray 300 flybridg

"I have a Sea Ray 300 flybridge with twin MIE 260 engines, factory without modifications, ~800 total hours with Thunderbolt IV ignition. The port engine just won't make power and tach up but the starboard runs beautifully as always. I have had a cruiser for over 20 years and I do my own work unless it is extreme or I don't want to buy the tools. I have checked the fuel system for water / comtaminants-it's clean. I have changed both filters. I replaced the fuel pump (factory original) but the engine it still didn't develop power, smelled very rich and used a lot fuel. I had the carburetor rebuilt by a very reputable local shop and replaced it. the engine runs better but still max 2900 rpm with the starboard engine helping at ~3100 rpm. I ran it for about an hour but the port engine is not developing full power. I also have trouble with it dying at idle (a real piss-off when docking in the wind) after I set the idle at factory spec. The engine starts easily and runs well except for the idle and power problems. I am thinking timing (ignition module puked) or air leak on the suction side of the fuel pump, although the tanks are aluminum and in new condition with clean internals. My next move is to check the timing and perform the fuel system test under load. Any help from seasoned mercruiser guru's would be appreciated. As you know, there's a lot of bogus info out there."

May be a weak coil or carb has

May be a weak coil or carb has issues. Pull the plugs and see what they look like. If it's rich
your choke may not be opening or jetting is off
or maybee they lost the accellerater pump check ball witch would alow vacume to draw fuel through the cirt. and get worse as rpm's increase. Also at 800 hours I would be checking compression and perform a leak down test to verify health of engine.

Kurt

I also noticed that the port e

I also noticed that the port engine diesels when I shut it down after running hard and it has done this since I got the boat 8 years ago but the engine ran fine until last season.

"Plugs are medium brown, almos

"Plugs are medium brown, almost new and all look about the same. It idles pretty smoothly so the compression seems reasonably balanced. The carb works better since it was rebuilt and the engine runs better but still no horsepower."

"Run on could be several issue

"Run on could be several issues but the most common are Idle to fast, Lean mixture, Timing too advanced, and top end dirty (IE carbon build up) Also good to idle a few after hard run.
assumptions are the mother of all **** ***.
verify comp with guage and perform leak down test
to verify health of engine and see what your working with. Also could be a flow restriction in the intake or exhaust (IE shutters) keep up the diag and soon The issue will come to light.

Kurt"

"Swap coils between engines to

"Swap coils between engines to see if the problem follows the coil. If it doesn,t swap tachs. Next, swap ignition modules. Have someone put a timing light on both engines at 2900 RPMs to compare advance. Check the exhaust shutters to see if they are functioning."

Does it still diesel? Yes? T

Does it still diesel? Yes? Throttle cable needs adjusted so it will close when engine is off. Adjustment may be part of the problem. How well is the choke working? Opening all the way?

"Thanks for the suggestion, sw

"Thanks for the suggestion, swapping known good parts is better than buying new ones. It dieseled last night when I got done flushing the manifolds. The throttle adjustment is unchanged and closes to the idle stop. Choke is the mechanical type and opens all the way."

The mufflers on this boat are

The mufflers on this boat are the canister type with the exhaust out the top of the canister to the hole in the side of the hull a la modern Sea Ray. Where are the shutters?

"Robert, am reading this with

"Robert, am reading this with interest, I seem to have a similar (ish!) problem, when I return the boat to idle, it smells really rich. I can't get any more than 3000 rpm, let us know how you progress as I'm slowly working through a long list of possibilities!"

Someone found a plugged canist

Someone found a plugged canister muffler recently and I think it was a power loss issue. I'm not sure if it has shutters on the inside if there on the outside of the exhaust. Call your dealer mechanic.