Mariner 40hp 2 cylinder prop question

[jestor68]

Re: Mariner 40hp 2 cylinder prop question

I find it interesting that the Mercury(Merc and Mariner are same thing) prop calculator came up with 13"
and you've tried everything BUT that.

A possible reason for the motor cutting out at 5K rpm might be that the reed valves are worn(fluttering at 5K) and need to be replaced. If unloaded, that motor will rev until it self-destructs. There is no rev limiter per say.

 

[anzomcik]

Re: Mariner 40hp 2 cylinder prop question

Jestor I got my first prop truely thinking I would be in the ball park, the 14 four blade. After seeing it that I was no where near anything I had thought I decieded that a 12 pitch (if following the rule of thumbs) would put me further in the sweet spot. Also I was nervous about being over proped again with the 13 (hind sight I feel you are correct with the 13, it would have really sucked if the 13 wouldnt pull me out of the hole good), so i would rather for the time being have to throttle back until I get my set up finialized.

Steelespike, Just because I dont have near as many posts as you doesnt make me a rookie, I have have owned 8 boats and 10 outboards and 1 I/O all of which I have worked on and set up to run propperly. I really do enjoy having a person like yourself to bounce ideas around on.

I tried tonight inbetween thunder storms to take a video with decent audio to show you what I am talking about. You will have to listen carefully because well the video isnt the best and I was alone. You can hear the motor run smooth for the first half but little past midway of the 6 secound video I gave it full throttle and you can pick up the sound of what I am calling the rev limiter, you will see the tach fluxuate, I do not loose any GPS speed when I am at WOT either. I am at 5480rpm with about 75-80% throttle (that is a guess basided on control position)

Tell me what you think the sound I am calling the rev limiter is.

 

[steelespike]

Re: Mariner 40hp 2 cylinder prop question

I'm thinking the timing may be advancing too far.
There may be a mechanical setting that is supposed to limit the timing advance.
Even sloppy linkage might let it slide past ideal advance.

 

[steelespike]

Re: Mariner 40hp 2 cylinder prop question

Any luck figuring out what's up?

 

[anzomcik]

Re: Mariner 40hp 2 cylinder prop question

I got 80% installed my CMC tilt trim/set back plate tonight (my motor did not have power trim). I wanted to wait on any further discussion until this set up was complete. I will be tieing up loose ends tomorrow and I hope to have the motor height adjusted this weekend.

I am hoping with the motor back an extra 6 inches, and lifting the motor heigth 2.5 above the bottom of the hull that I might be able to get the 4 blade to spin. I need to make sure that height doesnt effect cooling pressure, so I will post back with the findings.

As for the rev limiter/high speed missing? My school of thought right now is it isnt happening until I hit 5500 rpm, my max WOT, So I dont think I am hurting anything by running it if infact it is an ignition glitch. The motor runs smooth right now, I will do a complete ignition look over this off season unless somthing happens that requires me to look into it sooner.

 

[steelespike]

Re: Mariner 40hp 2 cylinder prop question

CMC,Thats a nice addition. Should really help to fine tune the setup and get the prop in slightly cleaner water.
A checked your video again it appears it goes from 5480 to 5470 and on down.A rev limiter would cut in somewhat higher than the max rated rpm and maintain rpm not lower it to something way less.
Anyway good luck with the CMC. Hope you can get all the performance that is there.

 

[anzomcik]

Re: Mariner 40hp 2 cylinder prop question

I had a very short window to try out the addition today. Water was fairly choppy, not ideal by any means.

I tried the 14 pitch 4 blade today mainly because i already knew I was underproped with the 12pitch.

I got 31mph, 4850rpm with the fairly rough conditions, so I picked up +-3mph and 300 rpm by setting the motor back 6 inches and raiseing the motor to 2.5 for the bottom of hull. the motor pulled much better out of the hole when compaired to the 14 pitch before the cmc.

Not a bad gain in my book. It leads me to think that when i do get another prop that maybe a 14pitch three blade might be correct. Not sure I will have time tomorrow to use the boat with the 12 pitch.

 

[steelespike]

Re: Mariner 40hp 2 cylinder prop question

Thats a really nice improvement. If you didn't have any venting issues you may be able to raise it some more.

 

[steelespike]

Re: Mariner 40hp 2 cylinder prop question

bump