96 Evinrude 50 prop/rpm questions

[michaelj1978]

I'm currently running a 96 Evinrude 50hp on my 18 foot aluminum jon boat (don't know the weight, but it has full interior). <br /><br />A problem that I'm having is I'm running a 15pitch prop and the rpm's at WOT are going above 7,000. Of course I don't keep them there, I try to run it at about 5,900rpm's for top speed. <br /><br />The highest prop pitch I can get for the specific motor is 19. What are the likely effects of going from a 15 to 19 pitch. Run smoother? Faster? Less RPM's?<br /><br />Also...The motor has tilt/trim buttons on the motor itself as well as the throttle/control box. The buttons on the motor work fine, but the ones on the control box are no longer working? Could that possibly just be a fuse or a larger problem.<br /><br />Thanks!

 

[ob]

Re: 96 Evinrude 50 prop/rpm questions

Hard to imagine a 50hp rapping 7000 plus pushing an 18 ft anything with a 15" prop,but if that's what you're getting then I would recommend the 19" and give it a go.If you can get the WOT at 6000 with a medium load ,then you would surely pickup some top end.Must be a very light boat.

 

[DJ]

Re: 96 Evinrude 50 prop/rpm questions

You can figure 200 rpm's for each in of pitch-up or down.<br /><br />A 19" still won't get you there, but it may deliver more speed.

 

[BoatBuoy]

Re: 96 Evinrude 50 prop/rpm questions

Are you sure you're tach is accurate?

 

[ledgefinder]

Re: 96 Evinrude 50 prop/rpm questions

Definitely check that tach...

 

[walleyehed]

Re: 96 Evinrude 50 prop/rpm questions

another item you will notice with a flat-bottom jon is that the faster you go, the more wetted surface it creates because of the design of the hull. You will reach a point where the 200RPM per inch doesn't follow suit...it will become 300-400 per inch.( I'm talking DROP when increasing pitch)<br />This being said, I agree with the guys above on checking the tach.

 

[michaelj1978]

Re: 96 Evinrude 50 prop/rpm questions

I'm pretty sure the tach's spot on. I idle around 1,200rpms. This week I'm going to trade in the 15 for a 19'' and see how well it works. I went and bought a cheapo 17 inch aluminum Hustler prop (60 bucks) and it gave me better top speed and lowered the revs about 300rpm. I think the 19 will leave me in a safer range at WOT. <br /><br />And even if the 19 leaves me at 6,500 and I want to be at 5,900 under WOT, is there any way I can adjust (probably lenthen) the throttle cables so that I can just hammer the throttle down and not worry about exceeding the recommended range?

 

[james082273]

Re: 96 Evinrude 50 prop/rpm questions

Where is your ventilation plate in relation to the bottom of your hull? You may be able to lower your engine and drop your RPM’s that way also. Probably want the plate even or slightly higher than the bottom of the boat.<br /><br />Those 40-50 rudes have a pretty lower gear ratio in the lower unit. Something like 2.42 to 1, don’t know exactly from memory. I have run a 14 pitch on my Tohatsu 40hp and that works out to a 18.5 or so in your rude. But I only have a 15’ boat (400lbs dry). It dropped my RPM’s to much for my taste. <br /><br />BTW-Have you measured the speed? Unless you have some massive prop slippage in there or your tach is wrong you might have a world record 50 horse on a 18' boat!

 

[walleyehed]

Re: 96 Evinrude 50 prop/rpm questions

Ya got some good info from some good guys here.....I'd seriously be looking into the tach, because if it really isn't turning that high and you repitch to show it's where you want, you may overload and kill that engine in a short time..

 

[Mark42]

Re: 96 Evinrude 50 prop/rpm questions

I know I'm a little late to put in my 2 cents here, but I think the tach setting is off because:<br /><br />1) the '96 50hp should idle much lower than 1200, more like 750 - 800. <br /><br />2) the Powerpack rev limiter will not let the RPM's hit 7000. Cut off is closer to 6000.<br /><br />Of course, I could be wrong, but that is how I see it based on the info in my OMC manual.<br /><br />Mark