Honda BF50A limited power and incorrect Tachometer Readout

Hi,

I'm wondering if anyone can help out? I have a Honda BF50A which has previously been running well however, on our last trip we set away from the marina after carrying out all our pre users checks ie: oil, tell tale water ect and all seemed to be running well until we went to increase the power. With the throttle position being around 50% we noticed that the tachometer was reading was 1800rpm even though the engine seemed to be running a lot faster - it was at this point we went to increase to 100% throttle to find that the vessel would only do 10 knots at WOT with a readout of 2200rpm. The engine runs smoothly at idle and WOT which is leading me to think that the engine has either went into a guardian mode or not talking to a component which controls the engine speed signal. We got the vessel lifted out to carry out some annual maintenance and thought that it would be a good opportunity to investigate the engine related issue in more depth. We have had the following checked professionally:

• Carburettors removed and ultrasonically cleaned (no debris found)
• Spark plugs replaced
• Fuel lines checked inc primer bulb
• Replaced tachometer (bullet type)
• Changed fuel filter
• CDI unit replaced with a good known secondhand replacement
• Fuel lift pump replacement

We are at a loss now and looking for some guidance from Honda owners/technicians who have experienced the same issue.

The vessel is a warrior 165 and used to do around 25knots but now struggles to get to 10 knots.

Thanks in advance
steve

The key to my thought here is that the engine seems be running smoothly at idle and at 100% throttle. This would have me thinking/wondering if it's getting hot, even though the tell tale is showing OK.

When was the last time the thermostat was inspected?
How old is the water pump impeller?

Beyond that, I'm stumped. I'd have to have the motor in front of me and start with the basics - like compression readings.

Hi Alan,

Thanks for your reply.

In relation to the thermostat and impeller- both have been replaced recently with genuine replacements including gaskets.

I visited the boat today to carry out some more testing and I used a digital tachometer to check the actual engine speed - on WOT underway it was achieving only 3200 RPM but running smoothly however . Another point to note is that the engine is responsive up to this restricted engine speed.

In terms of compression I'm led to believe that this issue would be more apparent on startup etc?. We have assumed these would be ok as we have very little crankcase pressure however I'll put on my list of things to do on my next visit.

The mind still boggles!

Cheers

What prop size?

Hi Alan,

10 x 14 RH which we were told was the correct sizing for the application used - The engine has ran up to full speed with this prop before.

Cheers

Hi,
Checking compression is a great idea and while doing so, take a look at valve timing. Make sure the belt is tight and in good shape and hasn't slipped a tooth or two.
This doesn't seem to be valve adjustment related but if you have no history of that having been done, you might consider doing that too.

Good luck.