Tried larger prop - engine stall

[ispaydeu]

Hello all,

Last August I bought a "new to me" boat, but it was definitly not new.

It was a 1976 Invader Continental 18' boat with a inline 6, I believe 165 HP.

Anyways, when I got the boat, it came with 2 propellers (one on it and an extra). The one that was on it for most of the season last year was the smaller of the two.


Over time, I was hoping to increase speed so I tried out the larger propeller. I also noticed that I was maxing out the RPM on the gauge when at full throttle on the smaller propeller. After doing reading in my manual, I found out that the WOT should be at 4800 RPM. So, that further help indicate that I could go to the larger propeller.

The other propeller, was not that much larger and definitly had some more pitch. In my original calculations last year I thought it would bring down my WOT closer to the 4800 RPM.


Anyways, when I went to use it, occasionally when shifting into forward or reverse, it would make the engine stall. It was almost like the weight of this propeller or the size of it was enough to make the idle RPM cause a stall under the load.

It would not stall everytime, but it would definitly do it if the engine was not warm enough. And when it didn't stall, it would sound like it would until it got it spinning and it would be fine.


So, my question is, do I just need to adjust the idle RPM to be slightly higher? Should I just go back to the previous propeller (I did occasionally have this issue, but was MUCH more rare).

I am thinking I just need to increase the idle RPM a little bit, but not sure.

Thoughts?

 

[QC]

Re: Tried larger prop - engine stall

Welcome aboard!! I am thinking you (we) need some more info and maybe we can help narrow this down.

1) Make/model? I am guessing this is a Mercruiser, but not positive.

2) Take a look in the I/O section. You need to understand the Electronic Shift Assist (ESA). This may be the source of the intermittent stalling.

3) Yes, higher pitch could cause issues too but I kind of doubt it. Don't increase idle past what's recommended. You'll find links to manuals there as well.

4) We need to know what the two different pitch's are and we need the actual (accurate) RPM you are seeing with each.

You will generally find good and helpful responses here. Feed us more info and we'll get this closer.

 

[ispaydeu]

Re: Tried larger prop - engine stall

Excellent, I will try to get that information tonight.

I have not taken the boat out this year, so might have to wait on the RPM question until I get to take it out.

I just know my wife is going to kill me if I don't get it fixed, she's embarassed when we go to pull up to a dock and it stalls and then we look like a bunch of fools... Which can't say that I disagree.

Her solution is just to put the previous prop on, but I would rather not as I know that at WOT the RPMs are too high with it. But then again, we plan on pulling some folks around on tubes this year and having larger groups, so the smaller prop might work out well for the heavier loaded activities that we plan on. In which case I suppose I could just try to not take the boat abot the WOT recommended RPM.

But I will get you all of the information and post it soon.

PS I have been reading the forums a lot over the last couple weeks and have learned a ton already.

 

[fishrdan]

Re: Tried larger prop - engine stall

I doubt it's a prop problem. Do some searching over on the I/O forum for your problem.. If you have a Mercruiser, look up problems associated with a bad lower shift cable.