Loss of power at full throttle - Honda 25 HP

[Venky]

Hi,
I have a 1997 25 Hp Honda on a 14' Twin Vee, center console. I bought the boat a couple years ago and the boat ran fine when I tested it. Since then I installed a CMC PT 35 Tilt bracket and the boat has rarely gotten on plane since then. As I open the throttle, the motor seems to bog down and pick up intermittantly thus causing the boat to not plane. The motor idles very well, starts up right away and never shuts down while running.
I was told that it was plugged up carbs so I had the carbs rebuilt, plugs changed and all fuel lines and vacuum lines replaced. After the service, the boat still bogs down at full throttle. If I pull back the throttle, the boat runs fine.
I am being told that the CMC bracket probably raised the motor so I am hitting the rev limiter as my RPM is too high and I need to increase the pitch on the prop.
The prop I have is a Stainless Steel prop and does not have any marking on it to determine the pitch.
What should I do to get the boat running back up again.
I could use some help and advice to test stuff before I start making changes on recommendations that may or may nor work.

 

[QC]

Re: Loss of power at full throttle - Honda 25 HP

"still bogs down at full throttle" and "hitting the rev limiter" seem mutually exclusive to me . . . Can you help clarify?

 

[Venky]

Re: Loss of power at full throttle - Honda 25 HP

When I open up the throttle, the feels like the motor is stalling (with a hollow noise) and then picks back up again. (which I refer to as bogging down)
I do not know what a rev limiter sounds or feels like. I was told by the mechanic who tested the boat after he fixed the carbs that what I call bogging was actually the reve limiter.
Hope this helps clarify the issue.

 

[QC]

Re: Loss of power at full throttle - Honda 25 HP

Well the rev limiter should only kick in at the very highest RPM and corresponding speeds. It is designed to keep the engine from exceeding a safe RPM. That would indicate that you were under propped (low pitch). Or, it could indicate "ventilation", which would happen while attempting to plane the boat, and the RPM rises rapidly, but the boat doesn't go any faster. That might "feel" like bogging (not accelerating) but it would sound just the opposite, more a of a free revving, annoying, Bumble Bee sound. Now if that Bumble Bee had got a hold of some bad nectar, and started to fart excessively that would sound like a rev limiter kicking in. But I can't correlate what you describe with that.

The bogging down, if the engine is running right, would indicate too much pitch or being over propped. That's why I am struggling here. If it just doesn't want to plane at full throttle, and the RPM is staying low trying to grab the water and push the boat up and over, I would be concerned about too much pitch or a problem with the engine. If it is revving up high, starting to fart, and not getting on plane, but you can back out of the throttle and it gets the job done better, then I would be thinking a prop tweak like cupping or a different prop, or lowering the motor some to eliminate what sounds like ventilation (prop sucking air off the surface).

 

[Venky]

Re: Loss of power at full throttle - Honda 25 HP

Thanks for your reply. I will pay a little more attention to the problem the next time I take it out. By your explanation, it seems like the rev limiter as the sound of the motor changes when I loose power. If I recall, it sounds hollow and not high pitched.
I will let you let you know by the weekend.

 

[Venky]

Re: Loss of power at full throttle - Honda 25 HP

I took the boat out thi weekend and looks like what I am experiencing is ventilation. I am sucking in air through the prop at certain trim positions. I checked the locaion of the ventilation plate to the bottom of the hull and the plate is a little higher that the hull.
There is no easy way for me to lower the motor as the CMC tilt bracket is not adjustable.
Will a prop change / re-pitch fix the issue.
Any suggestions will be appreciated.

 

[junior1113]

Re: Loss of power at full throttle - Honda 25 HP

eigther get motor back down or find a prop that is designed to run closer to the surface.

 

[steelespike]

Re: Loss of power at full throttle - Honda 25 HP

The Turning Point Rascal in the same pitch will do better.