Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

We have a Honda BF20 bought new about 5 years ago. It's always been used as the auxiliary outboard on a large boat, but this year we have it installed as the main outboard on a 12-footer.

Today was the maiden voyage as main engine. Outboard started fine and ran perfectly as usual, but a few minutes in, it lost power and started running erratically. Basically it would run at the set throttle setting for about one second, then give no power for a second, then accelerate back to the correct power for a second, over and over. It's like someone was opening and closing the throttle repeatedly in brief intervals.

After 20 seconds of running badly, the motor would cut out. Then it would start on the first pull of the rope and run fine for the next 2 minutes, then once again it would lose power with no warning and repeat the above.

Closing the throttle while it's acting funny results in a smooth idle. Opening the throttle just a little (say, 100rpm above idle) gives normal running. Opening it a little more it would start to pulse the power again.

Here's the funny thing. If it starts acting up and I kill it with the red ignition-cut button on the tiller, then start it immediately, it would run fine for a few minutes until it starts missing again. But once it starts missing, nothing I tried would get it to run right again short of killing and restarting it (or waiting for it to die of its own accord and then starting it).

The fault would appear after a few minutes at any power setting - WOT, half power, trolling etc.

Thinking it was a fuel problem, we tried running with a different fuel tank and fuel line. Still same problem. So it's likely something within the outboard that's not right.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Just the first thing that comes to mind....

The first thing to check is the prop size. If this motor was used on a large boat, it should have been propped with a high thrust prop.....a prop with a large diameter and very small pitch.

On a 12 ft boat the prop should be closer to the prop that comes with it ..a 4 blade 9 1/4 x 10.

In otherwords, it may be hitting the rev limiter.


Mike

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Hi Mike,

Definitely not the case. Motor has always had the stock prop fitted. Also, problem is intermettent (runs perfect for a few minutes then starts missing and dies) - if it was a bad prop selection I assume it would run badly all the time not every 2-5 minutes. Finally, like I said in the post, the "misfiring" happens even at just above idle - nowhere near the rev limiter.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Then back to basics..

How long has it been between boat #1 and boat #2? Is anything different besides boats? Fuel tanks? etc?

Have you changed spark plugs? Maybe a bad plug?

Have you drained the carburetor and checked for water in fuel? It does sound like it is an electrical issue, but water can cause usual responses.

If you have a timing light, you can put it on each spark plug wire and watch what happens to the spark as it fails. That may lead you in a particular direction.

Also, remove the big connector from the power pack and check for corrosion. Spray some WD-40 on it and reseat it several times to help clean it.

Check all ground connections, make sure they are clean and tight.

One more thing.....try disconnecting the kill switch and see if the problem goes away. Might has some internal corrosion built up.

Mike

I just reread and saw you have already changed tanks....sorry....I'm doing this while watching tv.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Boat #1 - all its life except this year.
Boat #2 - only used on the water once, yesterday

Difference is the mechanical setup (angle of outboard on transom is more "backwards" because it's a smaller boat), the height in the water is probably different (this is a long shaft outboard), the fuel system is all new (fuel tank, pipe).

The outboard has spent most of its short life in the garage - its innards are surprisingly clean so I don't think it has much corrosion yet, but I will try your suggestions anway. We'll be pulling the plugs a little later today.

The way it suddenly goes from running great to running badly, I suspect an electrical, or even more likely, a fuel issue. Reason being that when it does it, it seems not to be getting enough fuel.

Based on a fuel problem, how do I go about debugging the fuel system? How do I drain the carbuttor on the BF20? Any other suggestions? We are also going to try and extract the fuel filter and check that.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Mike is the expert, and I don't know a darned thing about the BF20, BUT, if that engine was on, say, my garden tractor, the first three things I would suspect are: (1) a clogged fuel filter; (2) air is leaking into the fuel line or; (3) the float valve in the fuel bowl is acting up because from your description it sounds like it's running through the fuel in the bowl, then not getting enough fuel to replenish it.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

I suspect the same things. Today we will be taking things apart to see what we find. Interesting thing I noticed on the boat - the fuel filter is always half-filled with air bubbles. Pumping the priming bulb makes the bubbles almost disappear, but then they are back after a few minutes. And the priming bulb goes soft after a short while running the outboard.

These exact same observations were made when we swapped to a different tank with a different fuel line and different priming bulb (but we used the same plastic fitting that clips into the motor fuel inlet - reason being we only have one honda one, so we undid the hose clip, removed the fuel pipe from the boat's internal tank, then connected the fitting to the new fuel pipe using a jubilee clip - so the problem is either within the motor, or related to the fuel connector that attaches to the motor).

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Air bubbles in the fuel filter is usually a dead give away that you have a leaking fuel line or a bad connector. I would suspect the latter.

One way to determine whether you have air leaks upstream of the fuel connector is to temporarily install a clear plastic fuel line between the pump-up bulb and the fuel connector. Start the engine and look for air bubbles in the plastic fuel line. If none, then the leak is somewhere between the connector and the filter.

Also, if you have an external Racor-type fuel/water separator (and you should install one if you don't) inspect the connections and the canister seal for leaks.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

If you think it is running out of fuel, have someone continue to squeeze the fuel bulb and see if it makes any difference.

You asked about how to drain the carburetor. If you look at the carburetor....on the front side of it and down at the bottom (bowl), there is a black slotted screw) Back the screw out a couple of turns (not all the way out) and fuel should come out through a clear hose to the fitting next to where the water indicator is (where it pees). If fuel does not come out, the hose could be pinched by the side panel or clogged with critter nests).

Mike

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Mike: we had tried constantly pumping the fuel bulb while it was running badly, but it didn't help on Saturday.

Today we took apart the lower halves of the plastic cover and had a good look. No corroded electrical terminals visible.

We extracted the spark plugs and they looked a very healthy golden-brown. Touched them to a metal screw while turning the flywheel and both gave a visible spark.

I found the slotted black screw, unscrewed it and collected the petrol in a clear plastic water bottle. There *may* have been a few bubbles that came out with the fuel, and in the water bottle I saw a little water at the bottom of the bottle beneath the petrol, but that may have been there from the bottle, so can't conclude anything.

We took the pipes off the fuel filter, but it looked very clean inside. We blew air through it backwards just in case (to clear out any dirt...)

Tracing the fuel system, it goes through the fuel filter inline with the pipe, then goes to the fuel pump in the back, then to a rubber-encased cylindrical thing near the oil dipstick (what is it - another fuel filter or some sort of fuel pressure regulator?), then into the carburettor. So we unplugged the fuel pipe from the carburettor nipple, pointed it into a water bottle and started pumping on the fuel primer bulb. We got a strong stream of fuel out of the pipe with every squeeze.

Turning the flywheel by pulling the starter rope also made fuel spray out of the pipe in spurts (spark plugs were still unscrewed at this point so no risk of starting it). So seems the fuel pump is healthy too.

We sprayed some WD40 into the carb's fuel inlet nipple and drained it out by unscrewing the black drain screw. Then reconnected the fuel pipe to the carb and flushed it with more petrol.

Connected everything up and started it. This is with the boat on land (using a hose and rubber headphones to feed the water inlet), so couldn't put it under any real load to test it under demanding conditions. However it managed to run at 3000 revs in neutral for several minutes without exhibiting the symptoms again. When it ran badly it did it in neutral too, so this is a good sign.

We will be testing it on the boat tomorrow or Tuesday. Based on today's tests and this thread I'm suspecting the problem could be:
a) Water in the float chamber - we cleared that out by draining it today. If this was it, motor should run fine tomorrow/Tuesday. If it doesn't run fine, then there are two more possibilities:
b) Fault with the plastic fitting that connects the fuel pipe to the motor's fuel inlet (leaky o-ring letting air in with the fuel or something like that). We still couldn't get the fuel filter more than half-full today, and no amount of priming with the bulb made any difference, the entire top half was filled with a large trapped air bubble, but motor ran fine regardless. In this case we'll buy and install a new fitting and see if that helps, or use Chawk's suggestion of a clear fuel line.
c) Problem in the carb (clogged jets, debris somewhere etc.). We'll be buying some carb cleaner shortly, but I suspect if things get to this point and it is necessary to take the carb off we might end up taking it to a professional mechanic and having him do the work.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

That black canister that is attached to the oil dip stick tube is a fuel vapor canister. It tends to accumulate water. Since you are in there, use some of the wd-40 to lubricate the dipstick tube and pull it off and turn it upside down to empty all water. Just pumping fuel through it, oriented the way it is, will not get all the water out.

I hope the problem is fuel, but, as I said before, a problem that comes and goes like turning a switch on and off is usually electrical or water in fuel.

I know you said that you checked the spark plugs and they looked ok. Sometimes the internal components fail and you can not see if they are bad or not. If they are Denso plugs....definitely change them to NGK CR5EH-9 even if you fix the problem in other ways. If they are NGK, wait to see how your other tests come out.

One other thing to check, as you are taking things apart is the hose that goes from the rear of the motor on the valve cover to the intake (muffler) of the carburetor. Make sure that is not plugged with critter nests or debris. That vents the crankcase.

Mike

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Did this problem ever get resolved or diagnosed? I’m having the exact same problem

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Wow, I forgot I posted this back in 2014 lol. It did get resolved. The mechanic had to replace the impeller. Basically it had several of the blades broken off. The outboard was overheating and shutting down every time it was used at any significant power setting.

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Never saw this post, but yes, that would have been my first thought. This is a very common problem with these little mind As. As well as impeller they have a habit of getting clogged around the anode at the bottom of the exhaust water jacket on the port side of the head. Basically a good cooling system service should fix it. On the odd occasion I've had to remove the cylinder head to clean out the passages

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Oh man I’m not so sure that is the problem with mine. I have a steady hard stream of water coming from mine which I would think is unimpeded. Do you think I that it could still be clogged with a hard steady stream of water coming through the system? I’ve replaced everything and drained the bowl of the carb. I guess that’s about all that’s left for me to check

LMF5000 said:

Wow, I forgot I posted this back in 2014 lol. It did get resolved. The mechanic had to replace the impeller. Basically it had several of the blades broken off. The outboard was overheating and shutting down every time it was used at any significant power setting.

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Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

The hard stream is only to let you know the water pump is fine, it doesn't mean there are no blockages. If your engine is doing as described above I would be doing what I suggested. That part of the service is often neglected

Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Well I’ve got some great news! I dropped the lower unit and took a look at my impeller. I bought this motor second hand last year and it worked flawlessly with very low hours so I must say that I was delighted to see that my impeller was cracked so it looks like I will be going to find a part tomorrow and hopefully be back on the water to try it out again. Man oh man I hope this fixes my issue. I’ve replaced plugs filters, drained the carburetor bowl and vapor canisters etc. I hope this works! I love this motor and will never own another brand of motor after this. Honda rocks!

iang6766 said:

The hard stream is only to let you know the water pump is fine, it doesn't mean there are no blockages. If your engine is doing as described above I would be doing what I suggested. That part of the service is often neglected

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Re: Honda BF20: "Pulsating" power delivery in one-second intervals. Briefly works fine if restarted.

Just a friendly note, you'll thank me later, do what I suggested,I can almost guarantee it's never been done