70 HP evinrude prop question

[scothorn]

I have a 70hp Evinrude on a 17ft Tracker, it currently has a 17 pitch prop on it. It tach's out WAY to high when opened up, hence I can't run it as fast as I'd like. Does anyone know the correct pitch I need for it to keep it under 6K rpm? I'm guessing a 19 might do it but not sure, any help is appreciated.
Thanks,
Scott

 

[hitace]

Re: 70 HP evinrude prop question

what RPM are you turnning right now with the 17 pitch.also if want a little more speed go with a steel prop

 

[scothorn]

Re: 70 HP evinrude prop question

it will easily tach over 7 k with the 17, but I don't dare do that for long. The boat was originally owned and used for a camera boat for a fishing show, so they changed the prop to get it on plane quicker with the added camera equipment weight and people.

 

[F_R]

Re: 70 HP evinrude prop question

I don't think a 2" increase is enough. If you are for sure running 17 now, go to a 21 at least.

 

[hitace]

Re: 70 HP evinrude prop question

woooo 7k thats way to much rpm what ever you dont run it anymore with that prop. you may have to go up to a 21 inch pitch but evey prop is different so it could be a lil more or less then 21 pitch but 21 would put you much closer to where you need to be

adding 1 inch of pitch =200-300 less RPM
subtracting 1 inch of pitch =200-300 more RPM

a cupped prop =100-300 RPM less

for example say you found that 21 pitch gave you 5500 RPM (thats what you should be runing at at WOT)and you bought a cupped prop 19 in pitch it will give you about the same RPM as the 21 pitch but you will have better hole shot and higher top end speed because the cupped prop grabes and holds the water better then a uncupped

also make sure the AV plate is 1 to 3 inches about the keel this will reduse drag giving you a lil better top end.but if you are going to raise the outboard up a notch do that before getting a new prop.liffting the outboard one notch usally will give you 100 more RPM

 

[ddaigle]

Re: 70 HP evinrude prop question

Something doesnt sound right, I have a 70 evin. with a 17 pitch on a light 17' bay boat and it performs well but will only turn about 5900 rpms and that is jacked up and trimmed. Sounds like you may have a tach problem or slipping hub or messed up prop.

 

[hitace]

Re: 70 HP evinrude prop question

yea i would agree something doesn't seem right with 7 k rpm you tach may be messed up.i would get that checked out before looking at props

 

[hitace]

Re: 70 HP evinrude prop question

if you are looking for a prop that will give you more speed 5 good ones are

"viper,raker,raker2,rebel and mercs x7 alloy props but only testing will tell the best for your boat

 

[rickdb1boat]

Re: 70 HP evinrude prop question

Check the dial on the back of the Tach. Make sure it is set on "6"...

 

[scothorn]

Re: 70 HP evinrude prop question

well the boat is older (1995) and the tach has been acting funny lately, (jumping around at idle) BUT seems to be alright when throttled up, even when it worked normal it was taching too high 6500 and up. I know the motor has a rev limiter at 6900 so it can't be more than that. But when at WOT it's really screaming. I mean it sounds too high. Gonna check the setting on the back of the tach. Could the tach be bad or could it be something else? I'm still convinced the pitch is wrong on the prop though.
Thanks,
Scott

 

[scothorn]

Re: 70 HP evinrude prop question

Also the boat really jumps out of the hole on plane REALLY quickly, like 2t seconds, that's another factor that leads me to believe the prop pitch is wrong.
I have to buy another prop anyway because I hit something submerged and took a small chip out of it. Very small. Will it hurt to run it that way until I get a new one? I'm at a dilemma because I can't check the tach without a prop, and can't buy a different pitch prop until I'm sure the tach isn't the problem. I've checked all my local dealers for used props, and no one has any!
Thanks again,
Scott

 

[scothorn]

Re: 70 HP evinrude prop question

Ok checked the back of the tach, there are 4 settings 10 pole at top 4 pole at bottom 12 pole on left and either 6 or 8 pole on right (worn badly can't hardly read it)should be the 6 or 8 setting right? It was set to 10.

 

[rickdb1boat]

Re: 70 HP evinrude prop question

That would be the pulse settings. Set it to 6. EDIT: Unless it specifically say poles. Then set it to 12 pole...

 

[scothorn]

Re: 70 HP evinrude prop question

it says pole for sure so 12? it's on 10

 

[scothorn]

Re: 70 HP evinrude prop question

ok changed it to 12, put muffs on and started motor. tach didn't respond correctly, I mean fast enough when I slightly reved motor. In other words I slightly raised the rpms and the tach didn't respond, but it did on the 10 pole setting. Any suggestions??
Thanks

 

[Seadoomanls]

Re: 70 HP evinrude prop question

Hey scothorn...I work a propeller shop down in Cape Coral, FL...actually...parents own the propeller shop...what you want to do is go to 19" pitch stainless with heavy cup...also let me get the diameter of this prop. As for the small knick...if you can ship it here to be fixed we can have it fixed and shipped back in a couple days...the chip isn't whats giving you funny RPM, but it will affect your motor...your prop will begin vibrating at which point your prop will wear at your shaft and housing...if you want the toll-free 1-800 number to my shop let me know. Called Burris Propller Service located in Cape Coral, FL

 

[rickdb1boat]

Re: 70 HP evinrude prop question

What brand Tach. is it? I would try it on the 6 setting...Post the results..

 

[scothorn]

Re: 70 HP evinrude prop question

Seadoomanls,
The tach was acting funny before I got the nick in it, but I appreciate your help. There's a shop down the road from me that repairs props. But I'm not sure I want to repair it just yet if it may be the wrong pitch. As far as going to a stainless, our lake here is Very shallow in places Especially at winter pool, with lots of submerged logs and timber. I'd rather stick with an aluminum prop to avoid major damage to the motor in case of another mishap. I'm not going to get a ton of performance out of that 70hp on an aluminum boat anyway. But I really appreciate your help. Thanks.


rickdb1boat
The tach is a stock bass tracker, I'm not sure the brand, I can look tomorrow and post it then. Also I'll try the tach on the 12 POLE setting and see what happens and post the results. Or did you want me to try the 6 Pole setting? Let me know. I just don't want to run the boat with that prop very long for obvious reasons, even with a small chip. I'll post as soon as I find out. Thanks Again everyone for your help.
Scott

 

[F_R]

Re: 70 HP evinrude prop question

As I understand it, a 70 has 12 poles, which is the same as saying 6 pulses.

 

[scothorn]

Re: 70 HP evinrude prop question

ok I'll change it to 12 and go test it and post the results as soon as I can. Thanks