Acceleration from idle

[Cat Nap]

Description of the problem.
Honda bf 25 about 15yrs old.
With the engine warmed up in neutral when shifted into reverse the engine accelerates slowley and tends to bog down. If I decelerate slightly and then accelerate slowley the engine revs up ok to full speed.
With the engine warmed up and in neutral when I shift into forward and a similar thing happens. However, if I decelerate slightly and then slowley accelerate the engine tendes to keep bogging down. If I move the throttle back and forth slowly gradually increasing the revs I can eventually get the motor to get past the he bogging area and then accelerate normally.
The bogging is the main problem but it seems strange that the conditions in reverse and forward are slightly different even though the motor is revolving in the same direction for both conditions.
I have changed 2 of the three carbs in the past.
I have all ways used gas preservatives regular dose or sometimes 2x rated dose in spring.
Lately I changed to Sea Foam brand (2yrs) and use 2x dose first and use regular dose from then on.
The motor is on a sailboat and runs for half hour periods most of the time. Perhaps I may run the motor for two hours+ two or three times a year.
The problem has improved slightly since switching to Sea Foam but only very slightly.
Could the timing be off slightly?
The motor starts every time hot or cold on the first rev even after winter layup and when stalling out after bogging down.
Any ideas ???
Thanks. Nick

 

[jgmo]

Hi Nick,

Welcome new member!

Questions....
Is this outboard's extension always submerged or is it trimmed/tilted up when not in use?

Electric start or pull start only?

Remote control or tiller?

I think the minor difference in how the engine responds might be attributable to the resistance of the prop rotating ccw in reverse and being less efficient than in forward. It's simply moving more water in forward and, therefore, more load.
Just a guess though.

I would do a cylinder contribution test on this one because it sounds as if it might have a weak or non-firing cylinder at lower rpm.

Some engines run pretty smoothly with a dead cylinder and can fool you. Well...they have fooled me at any rate.

It's simple to do:

First, take the wires off of the spark plugs and smear a thin coating of dielectric (tune-up) grease inside the boots. This makes it easy to pull the wires and slip them back on when performing the test. It's also good practice to keep the boots sealed with the grease to keep out moisture.

You may want to pull the plugs at this point and inspect/gap them. Do NOT wire brush them.
If they look that bad, just replace them.

With the engine running above idle (1200 to 1500 rpm), pull one plug wire and note the effect it makes on how the engine runs.
Put that wire back on and pull the next and so on.

The cylinder that makes the LEAST difference is the one to concentrate on.

Make sure that you use a DRY leather glove or rag to handle the wires if you don't have a proper plug wire pliers to prevent being shocked.

IF YOU WEAR A PACEMAKER OR OTHER ELECTRICAL MEDICAL DEVICE, DON'T TRY DOING THIS!!!

Someone else should help you if that's the case.

You may also want to try the test at idle if the results are inconclusive at higher the speed. The engine will be more prone to die at idle when a wire is pulled but that's just part of the process.

Also, you might have a good point about the engine being slightly out of time but Honda timing sets and belts are rugged and go many, many years without issue. The fact that it starts and idles ok makes me think that timing isn't the issue. But, you never know.
At any rate, I have no service literature in order to tell you how to properly check it out. You could, though, check to see that the belt is tight and in good condition.

In that same vein, valves that are out of adjustment might also produce symptoms like this. If the valves have never been checked/adjusted then that should be on a "to do soon" list.

A genuine Honda shop manual is your friend if you're doing the work yourself. Here's where to order one:

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

publications.powerequipment.honda.com

Good luck and please let us know what you find.

 

[NSDON]

Are you always running this outboard at low rpm? Say below half throttle ? Do you use the highest octane you have available?

I find sailboat motors tend to have problems from a lack of use and poor fuel quality from being stale- too much sailing and not enough burning of fuel at higher throttle. If your spark plugs are not a nice tan colour, that could be your problem. Extended running at high load gets everything nice and hot and burns off crap/varnish all the way through the fuel system. I use Sea Foam in all my carbed engines, been working great for 15+ years.