BF225 Honda surges between 1200 & 2000 RPM

I have a 2006 Honda 225 w/1,575 hrs. After accelerating and cruising at around 2000 RPM, the rpm's drop 100-600, then surge back. Geta ups on plane and runs flawlessly up to WOT. All filters are good, no water in fuel. Just purchased the engine to replace my 2003 Honda 225, installed on my boat using existing controls. Would appreciate any thoughts or advice. Thank you.

Have you tried a portable fuel tank incase the pickup gets partially clogged. Also check if the priming bulb is stiff when this happens...

Balcktimes, Thank you for your response. Have done all of that. We think we have it narrowed down to my existing control cables not being totally compatible with the new used engine. Just realized that when I turn the key on the battery and check engine light do not go on only the oil & water. Also, I have 2 fuel tanks main and aux., I have been running on the main, and just noticed that when I turn on the aux. tank switch, the gauge drops immediately to empty. Reversed polarity?

SeaSeaRider said:

I have a 2006 Honda 225 w/1,575 hrs. After accelerating and cruising at around 2000 RPM, the rpm's drop 100-600, then surge back. Geta ups on plane and runs flawlessly up to WOT. All filters are good, no water in fuel. Just purchased the engine to replace my 2003 Honda 225, installed on my boat using existing controls. Would appreciate any thoughts or advice. Thank you.

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This may be a little outside the box here, but always worth an exploration, since it is pretty simple to try.

Have you changed/gapped your spark plugs?

I offer this because I had a similar recent experience with my little 15hp motor. It was running rough and "surging" on a short fishing excursion, and I had a disabled fishing partner on board. Rather than risk any downside to our adventure, I abandoned the excursion, electing to deal with whatever issue I was having without needing to row home. The "surging" was one of the two cylinders failing to fire. I'd look there first.

On dry land, I pulled the plugs, and found one to be in embarrassingly poor condition. I changed out the plugs, re-gapped , and dang, if the problem didn't disappear.

Have you changed and gapped those plugs, etc., and run the engine again? Could be the greatest investment in your own understanding of your motor that you will ever make, for less than 20 bucks. My guess is that fuel has nothing to do with your problem. Report your findings to the Forum so we all keep learning. Cheers! Gleno

A tow back to the dock is always embarrassing.

I have not removed the plugs, which were in the engine I just purchased used. I agree, it's worth a try. Since you brought that up, I'll get a look at the coils. Dealer Had to replace one in my prior engine, but don't remember what the issue was. Going fishing this morning, will get a look this afternoon. I'll let you know the outcome.

SeaSeaRider said:

I have not removed the plugs, which were in the engine I just purchased used. I agree, it's worth a try. Since you brought that up, I'll get a look at the coils. Dealer Had to replace one in my prior engine, but don't remember what the issue was. Going fishing this morning, will get a look this afternoon. I'll let you know the outcome.

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Handle the coils with care, as they are very fragile. Definitely a good idea to look at spark plugs.

Sometimes the simplest things make the most sense. Wish I had suggested that. Also, I don't think it's uncommon for a bad spark plug to cause damage to a coil. As Deuxgrenouilles points out, they can be delicate.

If you look at my original post, my engine does not idle or run rough and is not restricted to perform at any RPM. It idles and runs smooth even when surging. It jumps up on plane and runs flawless to WOT. Definitley not a bad plug and poss. not a bad coil, although I suppose it could can be something intermittent. I do intend to try and learn how to perform tests on the coils before I turn it over to a mechanic.

Assuming the engine is structurally in good condition , it needs 3 things to run:
1)Air
2)Petrol
3)A spark.
There are sensors on the air intake manifold which monitor volume and pressure plus the throttle body with the IAC.
The Petrol supply starts from the tank, lift pump, VST,high pressure pump and filter, goes to the rail and excess is returned to the VST through the pressure regulator which in turn is driven by the intake manifold pressure which in idle allows for more return to the VST and less return when at high rpm/load therefore ensuring that the fuel pressure remains “constant” throughout the rpm range.Any excess fuel in the injector rail goes back to the VST ,more return to VST,less returns at high rpm.
And the third is the ignition -> timing spark plug fouls spark plugs etc.
Forgive me for not going into detail into what you have inspected so far but it should be somewhere in these 3 things.
I copied the following and paste the text:
If an engine is not getting enough fuel (this is called “running lean”), due to fuel pressure (regulated by the fuel pump and regulator), restricted fuel injectors, a vacuum leak or really anything that throws off the fuel mixture going in to the engine, this can cause the surge.
It’s also possible your idle air control motor is going bad. The idle air controller is simply a computer-controlled motor that controls idle. There could also be another sensor that is telling the computer to compensate, and in turn, this causes the idle to surge as it looks for the correct RPM level.
With computer-controlled engines, there is really only one way to figure it out, and that is to hook up a diagnostic scanner to the vehicle’s computer. That is because you need to see what all the sensors are doing in order to narrow down the issue.


It’s never a good idea to replace a part based on a guess, and it will almost always be more cost-effective to pay a repair shop for the time required to run a diagnostic than would be to just start replacing parts.

In case you are still looking to find the problem, you could look into these 3 things Air,Fuel,Spark and assuming there isn’t anything else out of the ordinary.

Heligeorge, Thanks for the info. I'm pulling the boat for the season this Sunday. My Mechanic will be checking it sometime after that. After looking at the paperwork received from the seller, most of what you mentioned here has been since 2018 repaired/replaced, cleaned etc. by the previous owner's Honda mechanics.