BF 50 runs very uneven

[PetterF]

Hi all,

We have a Honda BF50 that's about 20 years old and only gets used for a month or two each year.

It has an uneven idle and will sometimes start spluttering and lose power while underway. It struggles to rev properly and won't produce full power until the problem clears.

Last summer I cleaned the carburetors and replaced the O-rings and gaskets. Unfortunately, I only had time to test it at idle, which was still uneven.

The boat is in a very remote location, so I'd like to bring any parts or tools I might need before I go.

What should I check next? I have a vacuum gauge and can synchronize the carburetors, but should I also check the fuel supply? If so, what's the best way to do that?

I'm really looking for a troubleshooting checklist of the most likely causes, so I can research each one before heading out.

 

[jgmo]

Hi PetterF,

I have questions about the issue and not sure what to suggest about what you should be checking.

So far, I understand that the idle is "hunting" or uneven but it will run ok and produce full power at times.

Do you own the shop manual?

Have you ever adjusted the valves or checked timing and timing belt and belt tensioning components?

Is there a fuel/water separator?

Would you happen to have a spare portable fuel tank and hose to swap in for testing? If not, could one be borrowed?

Does it start easily or do you need to crank it for a time before it will fire and run?

When it starts "sputtering" and loses power but then recovers full power again...

...How often does it lose power, say, within a 30 to 40 minute run?
How long does it lose power before it recovers again? Is the recovery always back up to full song and power?

This might be a slog trying to figure out why it's doing this

 

[PetterF]

Hi PetterF,

Hi jgmo,

Thanks so much for your questions.

I realise I really have to be onsite to describe specific symptoms. It's a bit hazey as it was a year since I last saw the boat.

Do you own the shop manual?

No.

Have you ever adjusted the valves or checked timing and timing belt and belt tensioning components?

No.

Is there a fuel/water separator?

Yes. Inspected and even changed last year.

Would you happen to have a spare portable fuel tank and hose to swap in for testing? If not, could one be borrowed?

Good idea. I'll swap it out.

Does it start easily or do you need to crank it for a time before it will fire and run?

Unsure. I seem to remember I have to crank it a few times. But as said, not totally sure.

How long does it lose power before it recovers again? Is the recovery always back up to full song and power?

Last time I tried to use it it lost power after only 5 minutes of a third / half throttle usage.

What I am wondering is if there are some 'standard' go-to spare parts that I can buy now to take with me for any eventual repairs. We are way out on an island without access to a ship chandler, nor postbox for receiving orders/parts.

 

[William01]

How old is the fuel? Your symptoms doesn’t sound like stale fuel but it’s always a possibility?

Spare parts. Complete water pump kit, oil and filter, fuel filter, spark plugs, extra fuel/water filter, Seafoam or equivalent fuel stabilizer Service Manual(genuine Honda)

Suggestion. Label and keep all the used parts unless totally destroyed. Your location dictates parts hoarding.

 

[jgmo]

Hopefully you've been diligent about oil and filter changes. Oil degrades even just sitting in the crankcase.

A 20 year old engine that's never had the valves adjusted bothers my "sensibilities" but I also know Hondas are tough and I have rarely found problems with the valve trains even if neglected. Tight valves could though cause an erratic idle and or hard starting. I would not think that misadjusted valves would cause the intermittent sputtering and sudden loss of power. But sticking valves would. Often, checking and adjusting the valves can reveal other issues under the valve cover and by the nature of performing the task the timing can be verified.
You'll need the shop manual for doing that plus a tiny little metric wrench. I forget what size.
Genuine Honda available here:

Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com

Make sure you order the one that is for the 50A model and not the D. Also take advantage of the free stuff they have for the 50A.

While balancing the carbs may help with the wonky idle, I would also suggest doing a compression test. If she's not breathing right, that could help reveal the problem.

Sticking valves (or rings) could be due to deposit buildup. I prefer Techron Marine Fuel System treatment but there are many others out there.
Available at Walmart.
Hopefully the link works.

Robot or human?

My gut feeling though about the intermittent loss of power would be a possible ignition problem or a problem causing the engine to go into "guardian mode" for some reason.
Sticking thermostat
Faulty cooling temp sensor
Faulty oil pressure sensor

"Localized" heat spikes at full power are sometimes caused by mineral deposits. You might want to consider a vinegar flush in a trashcan. Others here...I think NSDON is one...have reported good results doing that and have posted how they go about doing it. Im assuming that none of the internal anodes have been checked/replaced on this "lonely" outboard. Something you shouldn't forget about especially if it's always run in salt water.

Does your remote or console have working warning lamps?

Ignition system problems could be any number of things. Number 1 on my list is a loose connection "somewhere". You would need to check connectors individually to rule that out. It's not alot of fun.
Beyond that, testing the ignition coils and plug wires, ignition switch and checking the kill switch could reveal something. These outboards vibrate quite a bit and things can shake loose over time.
Boat wiring harnesses located under the railing can flex and chafe. A strand of wire barely touching ground can cause havoc.

A few ideas but I'll come up with others, I'm sure, as I think about it some more.

 

[PetterF]

Lots to think about here. We inherited the boat so don't really know it's real history. The only thing we know is that he was a fastidious person and took care of services etc religiously. The only thing is that the engine has probably been on the island the whole time (since about 2001), so has not been in a mechanic's hands.

Regarding a vinegar flush, when I took off the air intake manefold there was a huge amount of white flakey material in and around. The solenoid was in good shape though. I just cleaned up what I could. So maybe a flush would be good to clean out what I could not. We are in the Baltic sea in Sweden so run in brine water, so not the saltiest of waters, but still enough I guess.

Getting the service manual may be a challenge, but seems pretty important as the problem could be one of so many different things. We'll have the boat in the water in a couple of weeks so I think I'll just have to do it from there, bit by bit.

Many thanks.

 

[jgmo]

Since you're in the European market, it might be best for you to obtain parts from Yumbo in Japan

YUMBO | Catalogs for outboard engines HONDA MARINE

Spare parts for HONDA MARINE outboard motors for European and American market. On the page there is a file table with which you can select the spare parts catalog for your outboard motor.

yumbo-jp.com

You might try emailing them and see if they can assist you in locating a shop manual.

Some of our Australian and Canadian members get their parts from yumbo and recommend them for price and availability.

Also...

When you cleaned the carbs, did you check the main jets and slow jet emulsion tubes closely?

Did you check all fuel hoses associated with the dashpot check valve closely for cracking?

Did you remove the idle mixture screws and clean the passages?

These carbs can trip you up if you miss analyzing and cleaning some critical areas on them.

 

[NSDON]

Get a thermostat, check the old one, it may be stuck partially closed and really ugly, get several new gaskets too. You can use the spare gaskets to check the thermostat in future.

Only flush the outboard in a barrel, these Hondas don’t like the muffs. Do the vinegar flush with the thermostat removed and the little telltale hose disconnected from the plastic tip- gives more room for the bits of salt to pass through the cooling system.

The shop manual will be very helpful- do you know a good Honda outboard mechanic who could advise you what the Euro spec outboard significant differences might be for this outboard? Likely related to emissions? You may find the North American spec Honda shop manual to be fine for most things- unless you can find the Euro manual. Check eBay locally for the manual, Honda sell there or maybe on Amazon? Only buy the Honda manual, the other generic manuals are too vague.

Yumbo only supply OE parts but they can be slow to confirm they have your part.

I’d suggest you first change the plugs, filters, fresh gas, and check the thermostat. If you find the thermostat is ugly, remove it and do the vinegar flush. Run it in the flush at say 2000 rpm for about 30 minutes. I used four 4 liter jugs of food grade white vinegar is a barrel.

Use a heavy dose of something like sea foam in the fuel while doing the flush. Note whether the old spark plugs were fouled.

If the flush etc doesn’t improve things, then go on with the other recommendations. Adjust the valves next, it took a 10 mm wrench and a flat screwdriver plus a feeler gauge.