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1998 BF90A power loss after rough waters

T

tjnson

New member
I've finally managed to get my engine running beautifully after a few weeks of tinkering around (rebuilt the carburetors, new ignition coil, cleaning grounds, and syncing the carbs). She now cranks great, idles around 950rpm, and will get up on a plane and maintain around 4200rpm no problem. Now onto the last issue!

The other day I am out running full throttle and everything is great, the water was calm and never really hit any waves. Fast forward to later that day when I was coming back into shore, I was running full throttle again, however this time I ran into some waves created by bigger boats around me. All of the sudden I lose power, my rpms drop to 2000 or below even when the throttle was still wide open... This is reproducible and only seems to become an issue after taking a few larger waves. Any idea on what could be causing this to happen? It has me pretty boggled... After letting the boat sit for a few seconds, it will start running again at full power...

Thanks for the suggestions! This forum has been a great resource to getting my engine running again.
 
I am tending to agree with Skooter on the limp mode or at least something similar.

First of all, can you get more than 4200 rpm? Or is that as much as you can get? You should be getting between 5500 and 6000 rpm at full throttle.

If you are not getting above 5500 rpm, the engine may be struggling and possibly overheating or having some sort of oil pressure problem.

Likewise, if you can get the 5500 rpm, then the motor may not be getting enough water for cooling as you are going over the waves, etc.

The audible and light warning system may not be working. Unfortunately, with that motor, the lights or horn will not come on when you turn the key to on, like the fuel injected models do. Sometimes the horn will sound as the motor starts up.

You can check the overheat light, audible warning system, and limp home mode, by taking the boat out into smooth water, then removing the red wire from the temperature sensor (located on the port rear top of the engine). Take a little jumper wire and ground the red wire to a good ground on the engine block. Put the engine in gear and run at full throttle. The red (overheat light) should go on immediately, then the audible alarm and then the motor will reduce it rpms to limp home mode.

If the red light and horn are activated but they are not with your present problem, an overheat may not be the problem.

This is going to be a process of eliminating things to the point that only the thing that is the problem is what is left.

Mike
 
First of all, thank you to both Skooter and Hondadude.

I have never gotten more than 4200 RPMs out of the engine while in the water. How would you suggest I go about getting more RPMs out of it? The engine seems to pee a nice strong steady stream while running, so I don't think an overheat is the problem.

I am now concerned about such low RPMs. I was not aware the engine should be getting up to 5500-6000.

Thanks for your advice!
 
What pitch is the prop ?----Is this a new installation on your boat ?----What kind of boat ?-------A lower pitch prop will get the revs up.
 
I just went through a job cleaning out my fuel system for the second time. One of the first indications that something was wrong was my boat losing power in the wakes of large vessels. What it turned out to be for me was the increased sloshing of the fuel in the tank was causing debri (gasket material in my case) to move around more and getting sucked up against the fuel pick up tube. If I killed the engine the sloshing would free the debri and once the water was calm again I could fire it up and proceed.

I'm not one to believe that everyone's problems are the same as mine but I can tell you that your symptoms are EXACTLY what mine were when it first reared its ugly head on my boat. Can you check your fuel tank for debri that could possibly impede fuel flow. If it is a hard task maybe you could use a temporary fuel tank (portable) to run on in the same conditions and see it that stops the issue from reoccurring.
 
Quick update!

After doing some more research as to why the engine would be going into limp mode, I realized that a lot of cooling exhaust water was coming out of the flush hose. I have ordered the parts to fix that and will see what that does.
 
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