Loss of top end

[jim mc]

I have a 175 Johnson 2 stroke that runs smooth, it will jump right op on plane.it pulls strong up to 4000 rpm / 30 mph.
After that the pull is missing ?There are no signs of prop damage that can be seen but I feel its not hooking up near the upper end
To be honest I rarely ever pushed the throttle and 30 mph was reached quickly now that seems to be all she' s got
Any thoughts on where to start.
I have 2 weeks before pulling the boat
Thanks
Jim

 

[boobie]

Re: Loss of top end

Is it running on all 6 cylinders. Check it out with a cylinder drop test.

 

[Tim Frank]

Re: Loss of top end

Has it ever exceeded those specs for you?
Is the motor new to you?
Was it always on the same boat?

Could be a trim issue, or prop is not right one.

 

[emdsapmgr]

Re: Loss of top end

Are we talking about a 175 crossflow or looper? A big difference. Pls post either the year, or model number.

 

[jim mc]

Re: Loss of top end

it's a 2002 with 450 hrs never abused , ive had it since 2008. Motor is pushing a 20'cc with tee top & curtains
It was demo @ 40+at sea trial, but in my usage I never exceeded 30 mph mostly due to sea conditions.
My main issue is that while rpm will increase with no break up there is no additional speed felt or registered on the gps

I think I can feel a slip. or at least cavitation or ventation I don't know the difference.

Thanks for the reply's and any further insight as to what may be the matter, btw the prop is 3 years old , I did have a spun hub
on the ss wheel that came with the boat I replaced with a $100 alum unit but no issues till now.
jim

 

[Tim Frank]

Re: Loss of top end

Does it live: 1) in or 2) out of the water?
If 1), maybe check for some waterlogging?

~ and~ are you 100% sure that you replaced with exactly the same spec prop?

 

[jim mc]

Re: Loss of top end

Tim
Yes its wet slipped, till mid November . The only penetration to the hull should be 2/3 screws for the Ducer, I replaced the unit my self in 2010. I reused the holes because they matched up with the old ones & I resealed with new sealing compound. Lets say that there is an issue here, i should unscrew the ducer and look for seepage ... let it run dry over the winter storage.?

And if that's the case, waterlog, wouldn't that be felt and struggle to plane as opposed to lack of top end.
I really want to get a look at the hub, spline and condition of the l/u oil that's first on my list. if its deep in the engine ..........
I have the winter to decide on the next one.

All constructive reply's welcome
Jim
Its all going to have to wait till I pull the boat in a few weeks

 

[Tim Frank]

Re: Loss of top end

~ and~ are you 100% sure that you replaced with exactly the same spec prop?

???

 

[jim mc]

Re: Loss of top end

Took the # right off the old one, its been on three seasons and this issue has only now come up.
Jim

 

[Tim Frank]

Re: Loss of top end

But you are saying that you never run it beyond that plateau,,,,????

 

[jim mc]

Re: Loss of top end

Yes,
The spec on the engine is 5000-5500rpm I don't think I ever touched more than 4500 rpm, that = 32 mph by choice.That came fast and easy, now its a long slow pull from 26-30 mph and it feels like that's it.The revs increase the engine gets louder but the linier pull is missing. so I don't just push the throttle to the limit for fear of breaking something ..just to see what happens if I do
I'm wondering if a seasons worth of bottom slime be contributing to this(yes it has anti foul paint)but its due in the spring

 

[Tim Frank]

Re: Loss of top end

OK... have you ever got to 5000-5500 since you bought it?
If yes, with the new prop have you ever got there?

i.e. are you 100% sure that this is a new condition?

 

[jim mc]

Re: Loss of top end

It demonstrated at 40+ @wot, the day I bought it(6 years ago) and not since. I don't need to go all that fast in my area.
and at this time its inability to jump to 30 +=right away nags at me
anyway i'll run it for the next two weeks with care
thanks
jim

 

[Tim Frank]

Re: Loss of top end

So it could be a gradual deterioration that you didn't notice since you did not need the top end.
Unless there is a reason to suspect the motor itself, I'd be thinking of weighing the hull and see how it compares to OEM spec.
Poly and F/G are not as "waterproof" as many believe.
You could be hauling around a bunch of waterlogged foam.