BF50D losing power

[sweetkismet]

I have a 2008 BF50D efi and its losing power at WOT.

I'm running a 18ft planing hull and when I open up the throttle it will get up to a speed of 25 knots at 5500rpm fine but then after about 5 mins the speed starts to fall and the revs drop to 3500rpm and the max I can do is about 10 knots.
Theres no misfire and the throttle is opening ok but it just seems to lose power for some reason.
If I cut the engine, restart then throttle up again, I get full speed again but will drop of as before.
No MIL and no alarms show.

Once back at the ramp I checked for DTC's and nothing.

Anyone got any ideas?

 

[hondadude]

Since you are not getting any codes, the problem will most likely be a fuel problem or an ignition problem.

Drain your vapor separator into a glass jar and see if there is any water in the fuel. Most likely not, since the motor runs on for a short time...but if there is water...then you will have to flush the system.

Try squeezing the fuel bulb when the motor loses power. If the power picks up, then you have a fuel feed problem.

Have you changed either of your fuel filters on the engine? Low and high pressure filters. Your filters could be accumulating debris and cutting down the fuel flow.

Does it have an in line water separating fuel filter? Has it been changed?

It may also be possible that there is a loose fuel line or fitting that is allowing air to get into the fuel system.

It could also be a faulty fuel tank, pickup or vent.

Once again, if squeezing the bulb helps, you can at least determine if the problem is in the engine or outside the engine, by using a 6 gallon tank and separate line as a test. If the problem goes away, then the problem is in the fuel system outside of the engine.

It just turns out to be a process of elimination.

Mike

 

[sweetkismet]

Hi Mike and thanks v much for the reply.

I did think it may be a fuel starvation problem and did give the bulb a squeeze while in the "fault" on the water but it made no difference.

Looking back I bought the engine just under a year ago and was told "its had a full service so no need to do a thing for a year or so". However, I found soon after that the water pump was worn and the lower unit oil was dirty. I think all he did was an engine oil change.

So, thinking now, I reckon you're probably spot on in terms of a fuel contamination issue, most likely high pressure side. I'm going to do a full service regardless, change all filters, clean oils, new plugs, check valve clearance etc. I'll also drain the VST into a jar as you suggest. Probably all next weekend now since my boat is at the yard.

Will report back findings when done.

Thanks again, Bob

 

[sweetkismet]

I serviced the motor today - new oil, filters, plugs etc. No water in VST or LP filter but both were drained and LP strainer washed in clean fuel.
The only parts in the Honda service kit I didn't change were those for the water pump as it was only done a couple of months ago (by myself so I know it was done properly!).

Took her out for a blast and she runs like new again.

The high pressure fuel filter in the VST was filthy - thick coating of black residue so I'm guessing that was the problem, fuel starvation.

I'm amazed the HP fuel filter is so small and no wonder it gets blocked so easily. Its a teeny little part.

Thanks again for all your help with this one.

 

[hondadude]

Thanks for the update. You have probably saved several people with the same problem from pulling their hair out.

Mike

 

[sweetkismet]

Just out of interest, I thought I would add a pic of the comparison to see just how dirty it got.
I have been using regular pump fuel in a clean tank and no sign of any contamination in the tank so the dirt must be just small suspended solids in the mix.
Sorry, its been an age since my last manicure...