115 prop pitch and high fuel consumption

[acclark]

I have a 1977 115 Evinrude V4. It still has the stock prop on it and there are no markings anywhere on it. At WOT, I turn about 4400-4500 RPM going about 27-30 kts. What is the max WOT RPM supposed to be for this motor? I borrowed a friend's 4-blade composite prop that had an adjustable pitch - from 14" to 20". I had never heard of a variable pitch prop, so I am not sure if that prop was worth anything or not, but at a 14" pitch setting, the RPM only increased to 4700 and the speed was lower at about 24 kts. With the max pitch of the prop, which was 20", the RPM was lower - about 4200 RPM at WOT and the speed was about 27 kts. The best pitch was 17" where the speed was about 30 kts. and the RPM was about 4600 at WOT.<br /><br />I don't know if that prop was any good or not, since a variable pitch doesn't seem as if it would work too well with a boat prop. I am still using the stock prop that was on it when I bought the boat and it has run great for over a year. <br /><br />I burn lots of fuel - about 6 gal/hr at 4000 RPM and 23 kts., but I don't know if this is standard for older motors.<br /><br />My questions are: Should I try a prop with less pitch to increase the WOT RPM's? Is there anything else that would cause lower RPM at WOT (such as too small a fuel line, dirty carbs, etc) that would not have changed over 150 or so running hours? If a carb. were gummed up or dirty, decreasing RPM's, I would think it would clean itself out after enough running or get worse, but not stay the same - so I've been assuming that the prop would be the only thing that would be affecting my RPM's.

 

[jimmbo]

Re: 115 prop pitch and high fuel consumption

That motor should be burning about 11gal/hr at WOT. which BTW is 4500 - 5500 rpm, preferably closer to the 5500 part. Running below 4500 is a death sentence for you engine Check the compression, max timing advance, run some engine cleaner or seafoam thru it. Stock OMC props have the dia/pitch marked on the hub end where the propnut washer fits.

 

[rickdb1boat]

Re: 115 prop pitch and high fuel consumption

Has it always been this way? I agree that you are running way to low on the RPM's if your Tach. is correct. If the motor is running well, a 15" prop would get you in the proper RPM range, but still a little low. I would first verify that your Tach is reading properly and go from there. Is it set on the proper setting(6)? What boat is this motor on?

 

[PGH Mike]

Re: 115 prop pitch and high fuel consumption

This is IDENTICAL to whats happening to mine. Has anyone had any luck on diagnosing it?

Maintenence:
New Fuel Lines
Cleaned Tank
Seafoamed it
Checked Stator for correct readings "via repair manual and a multimeter"

The boat was 300$... So i mean... Yea.
But its a great little boat, I like it, but the not getting on plane fast is a major issue.

This is my first boat, so i'm not sure how i should react, with me and my buddy "probally 350 lbs total" we are taking between 15-25 seconds to jump on plane at WOT.

After that its good, however, it'll only run, maxed out, 35 mph at 4300 rpm. Now, my buddies bass boat, granted its a 2003 and a 150, will jump on plane like nothing, and burn down the river melting your face at 6000 rpm going about 70.

Is this normal for a boat this old? Should i look at spark, or fuel, or compression, what is the normal compression for these engines? Cause if worse comes to worse, I don't mind doing a rebuild.

Like I said, it was 300$, i've already sunk about 300$ into it, and probally another 300$ more with redoing the tailor, and putting new carpets and whatnot in the boat, and paint. So for 900$ and some elbow grease it should be ok.