Momentary drop in RPM

My Honda 40 will be purring along fine at 2700 rpm, then drop a few hundred for a few seconds and return to 2700. The fuel filter is clean. Any suggestions?

I have actually had this problem at 3000+ since the motor was new, but since I have no need for speed I have ignored it.

thanks

 

Have you checked the coils? This type of "stumble" was very hard to track down in one engine I had.

 

How old is the engine? EFI or carb?
Does this continue to reoccur? Ie after it climbs back to 2700 rpm does it just keep running at 2700?
Does it occur within a few moments of start up? And after the engine the has been tilted up?
As the hp is 40, is the tank portable? Is the fuel tank an older variety with an open to atmosphere vent? or the newer style with the vent requiring a negative pasig to open

Electrical (as JEH suggested) and/or fuel would be the two causes (obviously)

If the engine is older you might run the engine with the engine cover at night and look for arcing from exposed ignition wires, coils etc.
You can take a spray bottle of water in a Windex bottle and carefully and lightly spray the wires which can reveal insulation breakdown. Normally though this would be an ongoing reveal at various rpm

When you answer the questions above it will help to offer some suggestions for cause

 

I am researching how to do this. Thanks for the suggestion.

 

Barry, Thank you for these great questions.

1. The engine is a 2008 model bought new in 2017 (I think it was lost in the dealer's storage). It has programmed fuel injection.
2. It does reoccur, and is starting to happen more often. It will stay at 2700 RPM after an occurrence for up to an hour, then dip again for 3-5 seconds, then back up to 2700.
3. It does not seem to occur at startup, but after the engine is warmed up. I do not use the trim because it is on a 27.5' pontoon boat operated at low speed.
4. Portable tanks are used, each with open vents.
5. I am not totally clear how how to check for electrical causes, though I have seen a general video (non specific to Honda) on using an OHM meter. I still need to figure how to do that on my engine.
6. I will recheck the fuel filter, tanks, and lines.
7. As I said in my original post, I have had a similar problem when going over 3000 rpm since the beginning, but since I don't normally run at that speed, I have ignored it. There also is a frequent dip/hesitation when I accelerate quickly. Do these symptoms help the diagnosis?

Thanks again,

Mark

 

Your answers negated many of some of the possibilities for the problems wrt fuel issues
Ie an older carbed engine with needles, seats, float and exhaust powered diaphragm fuel pumps could have been issues
Newer portable tanks could have been a sticky vacuum release vent if so equipped
Next time out the second the rpm drops squeeze the bulb to check for a fuel starved condition

In my first post I see that I had missed the night/dark water mist test words “with the cover OFF”