No added speed with more RPM

[Proline190FL]

I have a 1998 Johnson 115 I bought with a used boat. Compression is 125 on all 4 and it runs like a top. I took it out for the first time and when I put it in the water and give it gas the RPM's went up, but the boat did not move any faster than 4 or 5 MPH, just slightly faster than idle. Between 3000 and 5500 RPM the speed did not change. It acted a lot like a clutch gone bad in a truck. The strange thing was that after 10 or 15 minutes it started responding as expected and would get up on a plane. Can someone tell me what might be wrong?

 

[R.Johnson]

Re: No added speed with more RPM

Sounds like a spun prop hub. Take the prop off, with a magic marker, draw a line across the hub, and prop body. Try it again, if the lines do not match up, the hub is spun.

 

[kenmyfam]

Re: No added speed with more RPM

Spun hub 99.99999% certain.

 

[ezeke]

Re: No added speed with more RPM

On the 115, you don't need to remove the propeller to mark it for the test, just use the cotter pin as a ponter and mark across the hub.

 

[Proline190FL]

Re: No added speed with more RPM

Thanks. The only reason I did not look at a spun hub was the fact that after 10 minutes or so it started getting up to speed. Would being in the water for a while expand the hub and make it function properly?

 

[R.Johnson]

Re: No added speed with more RPM

I wondered about that also. I don't know the answer to that. That really had me thinking before I suggested spun hub.

 

[Proline190FL]

Re: No added speed with more RPM

Are there any clutches or parts that function like a clutch? I have only looked at a schematic of the gears; I have never taken the foot apart in one of these so I don?t know what else could be slipping.

I believe the boat sat for a few months on the trailer without being used. There is a slight bend to the tip of one of the blades so I would assume it hit a rock or something at some point. That could help the spun prop theory, but it could also indicate a damaged internal part.

I plan to replace the prop anyway so I will know if it still exists after that that it is internal, but it will be a coupel weeks before I can replace the prop.

 

[ezeke]

Re: No added speed with more RPM

If the prop is spun, it will get progressively worse over time. The propeller will slip at the time of greatest stress and heat from the exhaust will help it do that.

You could be experiencing cavitation or ventilation, two different but plausible possibilities with bent or chipped propellers.

 

[wilde1j]

Re: No added speed with more RPM

Are there any clutches or parts that function like a clutch? I have only looked at a schematic of the gears; I have never taken the foot apart in one of these so I don?t know what else could be slipping.

I believe the boat sat for a few months on the trailer without being used. There is a slight bend to the tip of one of the blades so I would assume it hit a rock or something at some point. That could help the spun prop theory, but it could also indicate a damaged internal part.

I plan to replace the prop anyway so I will know if it still exists after that that it is internal, but it will be a coupel weeks before I can replace the prop.

No!

 

[R.Johnson]

Re: No added speed with more RPM

The gearcase is direct drive with a moveable clutch dog for forward, and reverse. If there was internal damage, the slip would not go away, and would most likely give quite a clatter.

 

[kenmyfam]

Re: No added speed with more RPM

If the prop is spun, it will get progressively worse over time. The propeller will slip at the time of greatest stress and heat from the exhaust will help it do that.

You could be experiencing cavitation or ventilation, two different but plausible possibilities with bent or chipped propellers.

Very valid points