Paul311

First of all I would like to say hello to all of you. I am quite new to this forum and I have been picking up a lot of info already. As I am located in The Netherlands, you can imagine that we don't have so many knowledgeable people over here.

I own a F311-SR1 from 1989 and it has been a pleasure driving it. It has 2 x 454 magnum engines, all stock, 2 x 365HP each. 360 operation hours. At WOT, those engines are spining between 5000-5100 with the standard mirage plus 23p props.
Since one month, the starboard engine gives me some trouble. It performs well to 4600rpm, but pushing the throttles further I don't get more power from the starboard engine and I notice a slight variation in rpm's, so a slight swing (about 50rpm's) around this 4600rpm.
As far as I can see it is not an ignition problem, it seems more related to the supply of gas. Has anyone been facing a familiar problem? Is it so that just at this rpm level the second stage of the carburator needs to open? Could it also be a problem in the fuel pump where it is not supplying the required amount of fuel? A had once a vapour lock problem in this same engine, maybe that has a relation with it, I don't know.

Hopefully someone can help or provide me a way to determine the problem I am facing.

Thanks a lot in advance

Paul

C_Spray

iTrader: (2)

I would suspect ignition first, actually. Coil, cap, rotor, wires or plugs. Try switching these parts from the port engine to the starboard engine (one part at a time), and see if the problem follows the part(s).

I'm not sure where the carburetor secondaries are supposed to open, but a clogged jet might also cause the issue, although I would expect it to backfire then.

Paul311

Thanks for your info C Spray,

In fact, I do remember when I was driving the boat with both engines around 3000rpm, a sudden change to full throttle caused the starboard motor to drop rpm's to almost none, it backfires and than it picked up again.

I will proceed according your suggestion. You could be right, although the rotor, cap and plugs have been replaced 30 hours ago. Still the coil and cables could be the cause.

Thanks!

Cold Sweat

Paul, I had the same problem with the same engines. My problem was the carb inline filter. It was lacking 3-400 rpm. No backfire, just wouldn't rev up. Talk about a lean condition...

Paul311

Finaly I had some time available last week to look further into this issue.
Like already suggested, the problem was caused by the fuel/water separation filter.
I didn't suspect that filter because it was almost new, but yet it must have been picking up some pollution during a rough ride or something familiar.

Anyway, thanks for you help!!

Paul