Starboard Engine Cutting out above 3000 RPM

[trailshredder]

My 7.4L Merc, Bluewater inboard, starboard engine is cutting out when I hit 3,000 RPM. Fuel filters were replaced the end of last season. Tune up this spring with Cap/rotor, plugs and wires. Here is a video of it acting up. https://youtu.be/jViKKhFa4xc

 

[Bondo]

Fuel filters were replaced the end of last season.

Ayuh,..... So pull it off, 'n inspect it's contents, 'n install another new one,.....

 

[alldodge]

I'm thinking you may have a loose connection. Watching the vid I see the sync gauge deflect, also note it looks like the oil pressure gauge is about pegged. From this angle the rpm gauges don't appear to move much as the sync gauge does. Starboard tank is full and port is about half, engines cold, and gauge on far left is that the volt meter for port side?

 

[trailshredder]

The gauge at the far right is actually cut off from the video. It is the starboard voltmeter. Portside fuel gauge, which is the far left one has a bad sending unit, both tanks are completely full of fuel. So it is from left to right, fuel-fuel, oil pres.-oil pres., temp-temp, volt-volt. I haven't noticed the voltmeters reading anything but normal around 13 volts.

When I did the cap, rotor, plugs and wires on the starboard engine this spring, I noticed a wire that wasn't connected, so I referenced the port side engine to where it went and connected it the body of the distributor, wondering if it was disconnected for a reason.

Bondo - I will give the filter a try this weekend.

 

[trailshredder]

I have done a little reading and also read that Sierra filters, what is what I put on, are too restrictive for some mercruisers. They are a 10 micron filter instead of 25. Thoughts on that?

 

[alldodge]

I don't see the 10 micron being your issue

 

[Bondo]

Ayuh,.... I've run 'em both,.... No difference,...

 

[trailshredder]

Ok, Picked up a new filter today, I am heading up tomorrow to change it and inspect the new one.

 

[trailshredder]

New filter installed, issue remains. Other suggestions?

 

[alldodge]

I would check fuel pressure at the fuel rail, should be

Edit: wait, what is the motor serial number

 

[trailshredder]

Ok, I am a dumb a$$! It is real tight in the engine bay on this boat so not easy to see everything. Did some crawling around and found number one cylunder plug wire was completely off the spark plug. Was very windy so I wasn't able to take it for a ride but pretty sure that was the issue. If not, I will post back.

 

[trailshredder]

OK, test run tonight. It is better but sync gauge is still kinda erratic at 3300+ rpm. This time bounces from starboard to port about 3 each direction.

 

[alldodge]

It might be something like a plug wire breaking down, distributor cap and rotor, or distributor pick up.

Does the missing get worst above 3300 rpm?

 

[trailshredder]

It might be something like a plug wire breaking down, distributor cap and rotor, or distributor pick up.

Does the missing get worst above 3300 rpm?

​Yes, missing gets worse above 3300, runs like a beast 3200 and below. Sync gauge will hold steady at 0.

 

[alldodge]

Let me retract my comment in post 10 about fuel rail pressure, you have a Webar carb

Suggest getting a vacuum fuel pump tester and check pressure between the pump and carb, should be 4 to 7 psi. Check with it running and on plane because you could be running out of fuel.

Just for dumps and giggles, how about checking the firing order and how well the wires are attached

 

[Bondo]

Ayuh,.... Has a remote tank of fresh clean gas plumbed to the fuel filter/ fuel pump been tried,..??