Prop slipping??

[7lazy77]

The last few outings I have had, I noticed something going on & I am trying to figure out the problem. Took it to the dealer & he suspected something was pluggin up the carbs or fuel line, so he went through & cleaned them out. Took it out again this weekend & same thing happened! When I approach WOT (or close to) the boat will "jar" & feel like it is being held back with a lack of power. It it almost feels as if the prop is slipping?? This doesn't happen at lower speeds or even half-throttle, but does it close to WOT in BOTH forward & reverse gear. Any ideas?

 

[lncoop]

Re: Prop slipping??

What are the RPMs at that point?

 

[ezmobee]

Re: Prop slipping??

A slipping prop would cause the motor to rev up, not bog down. So that isn't it.

 

[TilliamWe]

Re: Prop slipping??

What are the RPMs at that point?

What he's getting at is, it "sounds" like what happens when a motor hits its electronic rev limiter. So if you are turning more rpms than you should be, the "computer" might actually be cutting off the fuel/spark to keeo the engine from over-revving and hurting itself.

 

[lncoop]

Re: Prop slipping??

What he's getting at is, it "sounds" like what happens when a motor hits its electronic rev limiter. So if you are turning more rpms than you should be, the "computer" might actually be cutting off the fuel/spark to keeo the engine from over-revving and hurting itself.

Actually, I was just trying to eliminate a spun hub as a possibility. As ez says, if he's not even reaching WOT it's not a spun hub, but I haven't heard enough to be convinced either way. That was my reason for asking. Good thought though.

 

[7lazy77]

Re: Prop slipping??

RPM's are around 4000-4500 when it does it. Engine hits that point & with a little "hesitation" it feels like it is holding back. Can't get anymore RPM's even though I still maintain the speed that I am at when it does it. (Sorry if I am confusing, just hard to explain). If I throttle down & then back up, it has no problem taking off until I hit that RPM range again.

 

[Lakes84]

Re: Prop slipping??

cavitation me thinks....

 

[QC]

Re: Prop slipping??

I think you mean "ventilation", and that would also cause a spike in RPM not a limit to RPM . . .

 

[Solittle]

Re: Prop slipping??

Ahhh - - what engine we be talking about?

 

[7lazy77]

Re: Prop slipping??

1994 Johnson 115 hp

 

[Bob_VT]

Re: Prop slipping??

RPM's are around 4000-4500 when it does it. Engine hits that point & with a little "hesitation" it feels like it is holding back. Can't get anymore RPM's even though I still maintain the speed that I am at when it does it. (Sorry if I am confusing, just hard to explain). If I throttle down & then back up, it has no problem taking off until I hit that RPM range again.

Okay your rpms are too low and you are not hitting wide open throttle.

Is this a new boat/motor to you?

What prop is on it?

Who set up the motor height?

What size boat and hull design?

We need more information to help diagnose the problem.

 

[7lazy77]

Re: Prop slipping??

Boat is fairly new (have had it for 2 months).
Came with a 13 pitch (steel) prop & I put 11 pitch on it (Solas aluminum purchased thru here).
Not sure who set the motor height? Boat was run on a river before & I now run it on lakes.
Motor is on a 24' pontoon. (problem happens rather there are 3 people on it or 13 people)
Thanks!

 

[cribber]

Re: Prop slipping??

Another consideration is what elevation do you run at since you're in Wyoming.

 

[7lazy77]

Re: Prop slipping??

I am running the boat anywhere from 6000-7000 ft. I have talked to the local boat dealer about the big change in elevation (from where I purchased the boat) & he swears that I don't need to have my carbs rejetted. Is he full of it??
The funny thing about the "mysterious problem" is when I took it to Nebraska over a month ago, she ran like a stripped ape, with NO hiccups like I am having up here now!

 

[QC]

Re: Prop slipping??

6000-7000 ft.

Doh!!! This is worth more than 20% in power compared to sea level

 

[rbh]

Re: Prop slipping??

^^^^^^
Time to hunt down some new jets for that elevation, you should have seen my old snowmobile bog out when I got to 8000 feet.

 

[7lazy77]

Re: Prop slipping??

So the big change in elevation is causing the motor to hesitate & hold back before WOT??

 

[lncoop]

Re: Prop slipping??

So the big change in elevation is causing the motor to hesitate & hold back before WOT??

Sure sounds like it. You know it's not ventilation or a spun prob hub since those present with an RPM spike and are not preceded by any kind of "hesitation" or "bucking" type sensation. If you believe the tech your carbs are clean and there are no fuel issues (other than the one that's being considered), and she ran fine at a lower elevation. If the duck quacks feed it.

 

[Philster]

Re: Prop slipping??

Wow... that's a big elevation 'hit' for a basic motor. Since it gets it's tuning from human hands, human hands have to get in there. Modern electronics on modern engines would make all the adjustments. Yours is hands on, so someone's gotta get in there.

 

[Lakes84]

Re: Prop slipping??

I think you mean "ventilation", and that would also cause a spike in RPM not a limit to RPM . . .

Yes you are correct.... Ventilation can lead to excessive slippage. Cavitation can lead to ventilation and/or slipping.