prop for a '55 evinrude fastwin 15

[Philip_G]

I have an old 15hp fastwin I use on a little 14' fishing boat.
the motor is running great but only pushes the boat about 10mph and gets to 3800RPM. It gets full throttle, the carbs been rebuilt, ignition gone through and replaced, it runs as it should otherwise.
I'm up at about 5800 feet and the motor has an aftermarket michigan wheel bronze prop of unknown pitch. Does it sound like it needs a little less prop to you guys too?

I didn't think the prop had any markings on it, but on closer inspection it says "michigan AMC332" it's not spun.

I don't know how long they've been in business, but I have no reason to believe the prop has been touched on this motor since the 50's or 60's. Michigan suggests a 3 blade 9x10 for my application, any way to figure out what a 332 is?

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

I assume you have fine tuned the high speed needlevalve to the best at that altitude?
Original prop was a 9" X 11" Max rpm rating is 5,000.Max speed at sea level is about 21 mph.
Look carefully for size numbers Stamped near the base of the blades or on the end of the hub.
A prop shop can likely measure the prop for you.
At 5,800 your power is down about 18%. Not sure about how much rpm an inch pitch drop will gain
but I would think a 9" pitch would work.They may be able to rework your prop.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

Yeah, it runs GREAT on the high needle, trolling... not as much. I just rebuilt the carb last fall and set the needles.
I'll look again for more numbers, maybe I'll email michigan and ask too. Can't hurt.

I double checked the throttle today and it runs all the way out to the end of the tapered disk that pushes the throttle linkage, no adjustment to get more travel there.

When my dad had this motor on a similar boat it towed a skier, but that was a few thousand feet lower.

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

Was the AMC332 on the motor when it pulled a skier? If it worked at lower elevation at least you know its a relatively normal pitch.It likely would need to be repitched for higher elevation.
As far as your idle be sure the speed is set about 650-700 set the mixture warm in gear.
Maybe you could try the motor at a lower level to try to get the idea if the prop is right in a normal conditions and the motor is in good condition.You might do a compression check. At 5,800ft it will be like about 12 hp when carefully tuned.should be able to make 20-21 mph.
It would probably be best if you could have the AMC332 repitched, standard pitch is 9" X 11"probably needs to be
at least 2" less.
Did a little research the Gale 12D10 uses a similar 9" X 10" prop.The Evinrude/Johnson 10 hp uses a 9" X 8"
don't know if the same shaft size.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

Unknown on the altitude, motor was bought and lived in IA most of it's life and was used to go up to canada to go walleye fishing so it's probably pitched for down there.
I didn't know they could re-pitch them. I'll look for a local shop, thanks for the idea.

part of the idle problem I'm sure is the 42 degree water and lack of thermostat, the motor trolls cold cold cold. It has compression in the high 70's. It does troll a lot better after running around the lake and getting the motor warm, but even then at full throttle with water as cold as it is now the discharge is barely warmer than the water temp

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

I know what you mean and I bet it really cools off at that temp.
If you troll a lot some suggest a step hotter plug.Also there is probably a crankcase drain
they keeps excess fuel in the crankcase from building up you might check that out.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

I took it to a prop shop. He measured it at a 9. 30 bucks to back it out 2 degrees. Hopefully it won't snap.

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

Hopefully it was the prop holding you back and not a tired motor.
When you say back it out 2" you mean reduce the pitch to 7"?
Your compression is ok but a little low probably wouldn't notice a performance difference without a speedo.
You might do a decarb with something like SeaFoam.This can remove carbon and free up, the rings if they are stuck.There have been a number of successful decarbing results reported here.

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

I just noticed that 9" is all;ready 2" less than stock.
I hope going to 7" isn't too much.
Maybe you should wait on the pitch change and try moving weight forward.
At 10 mph your probably not planing if you could get it over the hump she would probably
get over 4,000 still a little low but closer to a better top speed.A tiller extension
would put you in the middle seat.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

Hopefully it was the prop holding you back and not a tired motor.
When you say back it out 2" you mean reduce the pitch to 7"?
Your compression is ok but a little low probably wouldn't notice a performance difference without a speedo.
You might do a decarb with something like SeaFoam.This can remove carbon and free up, the rings if they are stuck.There have been a number of successful decarbing results reported here.

at this altitude the compression is fine.

they said degrees so I'm not exactly sure I guess.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

now you have me worried I've screwed this up. Maybe I'll call tomorrow and put the brakes on it.

 

[steelespike]

Re: prop for a '55 evinrude fastwin 15

As you say at that altitude your compression is fine.My worry is if it isn't planing its harder to estimate what pitch you need.If we can be sure its planing then pitch selection becomes easier.
Did you mention the elevation to the prop guy?On small motors a 1" pitch change is easily as effective as a 2" change on a larger motor. To little pitch isn't the end of the world and it would surely improve the ability to push a load at that altitude but you may have to watch the rpm and top speed may be reduced, not from your existing 10mph but from the potential max.

 

[Philip_G]

Re: prop for a '55 evinrude fastwin 15

As you say at that altitude your compression is fine.My worry is if it isn't planing its harder to estimate what pitch you need.If we can be sure its planing then pitch selection becomes easier.
Did you mention the elevation to the prop guy?On small motors a 1" pitch change is easily as effective as a 2" change on a larger motor. To little pitch isn't the end of the world and it would surely improve the ability to push a load at that altitude but you may have to watch the rpm and top speed may be reduced, not from your existing 10mph but from the potential max.

Yeah, I did. I told him it came from low altitude and I thought maybe it was too much because of the low RPM and he's the one that said "we can reduce it 2 degrees" I'm sure they deal with this all the time. If it's not right I'll be on the hunt for a used factory pitch prop, no big deal I guess.

it definitely doesn't plane now, with just me in it the bow is super high, if I move to the front it's a little faster but doesn't really plane, with two people in it I only get about 7.5mph but it rides nice and flat :redface: