Prop for 1977 15hp Evinrude 2 cycle

[davkrat]

I have a 1977 Evinrude 15hp 2 cycle on my Valco 14'. Dry weight of boat is 150 lbs, about as light as they come. The prop is a 9.5"X10" three blade aluminum which I believe is the OEM stock prop size. I've rebuilt the carb and replaced the plugs. With myself (260 lbs) and my 9 and 6 year old kids it maxes out at 5150 rpm for 15 mph. Just me I hit 5250 rpm and 16 mph. Gas and battery are moved forward under the bow and I'm running the trim on the lowest hole to keep bow rise down. Also have a fin mounted on the plate to help get the stern up, I'm considering building a jack plate to lift the prop as the ventilation plate is about 1.5" below the transom. It's a 15" transom but the motor is more like 17". I tried a 2X2 under the motor mount to get the plate even with the bottom of the hull and it got me up to the above rpm's and speed, before I was only getting 13 mph with the kids in the boat so raising the motor got me 2 mph with a load. Boat is mostly used for trolling for kokanee with the kids, I'd really love to be able to hit 20 mph. I also intend to use it in shallow rivers for duck hunting, hence the jack plate intention to get the skeg up as high as possible.

Reading online I've seen several people claiming to get as high as 24 mph out of similar motor and boat with a 10" pitch prop. Motor is rated for 5500-6500 rpm and I am falling 300 rpm below that at best. Seems like my motor just can't spin that pitch prop. I am looking to replace the current prop which is lightly worn, wondering if it might be keeping me from hitting the power band. First I am considering getting a 4 blade 8" pitch aluminum. Figure with the boat empty I will hopefully hit the upper end of the rpm range and with a load still be in the power band. Also for running shallow in the river with a hunting load the lower pitch and 4 blade should help get me on plane at lower speeds.

I would also like to get a second prop, maybe a stainless 3 blade 10" pitch. For chasing kokanee around the reservoir (currently a 20-30 minute run with the kids in the boat) hole shot is not as important as top end speed and for the time being the kids are still a fairly light load.

My question is will a 4 blade 8" prop get me in to the upper range of the power band.

Is the 10" stainless worth the extra cost if my motor won't spin my current aluminum 10" over 5500 rpm?

Is there some other underlying issue I should look at if a 15hp Evinrude won't hit the power band with a 10" pitch prop?

Video of running it with the riser block: http://www.youtube.com/watch?v=beheazk_ElA&feature=youtu.be

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

delete

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

delete

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

It appears your working hard to get the quickest hole shot.
Your hydrofoil is probably stealing 1 or 2 mph because your dragging it through the water.
Your trimmed down and you have added weight to the bow and the foil is keeping the bow down
I think that probably costing another 2 to 4 mph. A jack plate with luck will get the foil out of the water at speed
Eliminating that drag and helping to get the bow up.Trimming the motor up should add some speed.
Setup properly your boat lightly loaded should have about 1/2 to 1/3 of the boat in the water.
Is your speed by a gps? Presently your slip is at 22% a ridiculous number typical slip is usually 8 to 12% depending on the hull
and weight.
A 8" prop could add about 400 rpm but at 5650 and 12% slip(not likely with your setup) speed would be about 15 mph.
Is the bottom of the boat clean and smooth?
Is this boat a Jon boat? Set up right I think 5800 would be easy with the 10" prop.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Thanks. Yeah I agree the slip is ridiculous! That is why I am curious if it s not some other motor issue not allowing me to get up to higher RPM. The bottom is clean. Yes it is a small Jon boat with a deep V nose but very flat bottom from midship back. I was considering pulling the fin to see if the reduced drag is any better.

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

Is your speed by gps?Yes removing the foil should help speed.
But your trimmed down you need to trim up to try to get more of the boat out of the water.
Depending on the results perhaps move the tank back to the middle.
The boat probably has 4 or 5 keels to strengthen the bottom, these increase drag but not much you can do about it.
Sometimes a Jon will tend to be stubborn about getting the bow up. What is the bottom width?I have a feeling 32 or 36"
Depending on how the boat responds to proper setup 20-24 is certainly possible.
If you get the boat setup right your speed will go up and the slip will go down.
My 89 after market manual indicates the 15 hp rpm range is 5500-7000 rpm.
Are you sure the throttle opens all the way and is the link n sync correct?

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Yes the speed is off my fishfinder GPS. You can see it in the YouTube link above.

The throttle not opening all the way is something I was wondering about, not sure how to check that. As for the link being in sync I do not know either. What link should I be looking for? The sticker on my motor says 5500-6500 rpm, can't imagine they would sell these motors with props that could not get somewhere in to the powerband. I'm putting together another video showing the attitude of the boat with just me in it on plane. I believe it rides right where it should be with the front 1/3 of the boat out of the water, it definitely isn't plowing the nose.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Here's video of how it rides: 14' Valco 15hp Evinrude - YouTube

Added photos on the end of the carb when I poulled it apart, was surprisingly clean for an old motor that sat for 9 years without running. I've been driving it for the last 9 months though so it's not like I just pulled it after sitting unused that long. Going to see if I can pick up some Sea Foam today.

The boat has a 48" bottom and you can see that the fin is almost perfectly level with the bottom. I've tried trimming it out but all I got was too much bow lift and no gain in to speed. Really think there is something else to the motor that is not letting me get up to the max rpm's.

Here's basically an identical boat going 26mph: http://www.youtube.com/watch?v=xJqS56fl1Nc&feature=youtu.be

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

You should be able to check the throttle by opening it with the motor off and in forward observe the throttle position in the carb throat.
If you operate the throttle as you look into the carb you will see the throttle plate opening and closing.
Link and sync involves the amateur plate cam under the plate picking up cam follower at the correct point.
If you operate the throttle with the motor off and in forward you will see the components operating.
These components may be worn and/or out of sync. There should be a V mark on the cam that indicate where the cam follower should pick up. As the armature plate advances the timing it begins to open the carb as the follower makes contact at the V mark.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Looks like my cam runs out just a little shy of wide open. The adjustment bolts for the cam seem to be set all the way to the minimum. The link kicks in slightly right at the V symbol or maybe just slightly late. Here's some pics and video

Evinrude Carb Cam - YouTube

Idle



Full



Full plus

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

Sure looks like you can gain some rpm right there. Can you look down the carb to confirm the position of the throttle plate?

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

No can't see in it really. It butts right up against the front of the housing. Just picked up some sea foam and rented a compression tester. Going to do my jeep and this motor then maybe go blow them out this afternoon on the lake.

The cam roller does not have an allan nut adjuster on it like most seem to show on line. The plate has a center pivoting bolt and then a back adjustment bolt that rides in a slot. I just loosened them and maxed out the plate, it was pushed all the way in and I pulled it all the way out. Still contacts the roller at the V mark. Hopefully I'll gain a few rpms. Thanks for the help!

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

Maybe you can carefully move it with your finger or rig a pull string.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Was thinking of doing a pull string while out on the water.

The compression was only 65 lbs on each cylinder. They were both dead on at 65. Sounds like they should be 120-140. Might pull the head and throw on a new head gasket see if it helps. Did the seafoam which was fun playing in a smoke screen. Won't get a chance to run it on the lake to blow it out yet. Definitely won't be running high octane anymore if the compression is that low. The pressure gauge I rented was not in the best shape. It did get up to 65 and hold there after multiple pulls though.

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

65 is a little low but it's good they are the same and a Hand cranked motor usually is a little low. Did you check it after the Sea Foam?
I never did Sea Foam but as I understand it you can soak it to help loosen up the carbon.You need to position the pistons so the ports are covered. Lay it down with the plugs up and add the Sea Foam as directed.
The motor is designed to run on 87 octane;when you use High test it actually makes it harder for the motor to burn the fuel.
Probably not enough that you could tell without recording the performance.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

Thinking maybe I have a fuel pump issue. Going to order a rebuild kit as the old membranes looked hosed. Is it possible the fuel pump wasn't supplying enough fuel at WOT to reach the power band?

 

[jestor68]

Re: Prop for 1977 15hp Evinrude 2 cycle

I have been told that like new is about 140psi, and 120psi is considered to be the minimum for good performance.

Bottom line: low compression equals low power. Two stroke motors that lose as little as 20 psi suffer a noticeable power lose. Losing half of the like new compression results in a really noticeable power lose.

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

Your video sure seems to indicate a loss of power.
If the rings are stuck from carbon there is a chance the decarb treatment I described might help.
But I'm afraid we are dealing with a tired motor. The boat is barely planing.
And that video is a pretty honest result.
A weak fuel pump would normally result in a sporadic loss of power perhaps surging fading and perhaps stalling.
What year is your boat? I don't think it is 150lbs. I think the light boat is only 4'9" beam.
the others are about 220 And a 325lb beefier.
A healthy 15 will push any of them fine.

 

[davkrat]

Re: Prop for 1977 15hp Evinrude 2 cycle

I haven't had a chance to get it on the water. Hopefully tomorrow morning I can go run it. I had it running on the muffs this morning and noticed fuel dripping from the fuel pump. I went ahead and got the rebuild kit for the fuel pump.

I won't be surprised if it is just a old tired motor just checking all the small stuff first.

 

[steelespike]

Re: Prop for 1977 15hp Evinrude 2 cycle

If the pump is leaking it's best to make the repair.