Prop causes motor to rev high.

evilwind1 · Nov 5, 2008

I have a 19 foot 1969 Winner with a 1988115 (no pt/t) with a 13 3/4 R15mvc prop. When I first give it throttle the boat really jumps right up on plane. For a relatively heavy boat (2000 pounds I believe) it really throws you back if your not holding on to something securely. Once on plane she rides great, cuts through waves and is nice and stable. The problem seems that it's burning through alot more gas than it should and seems it's revving high. The tach isn't working so I don't know what the RPM's are. The boat moves along at about 35-38 mph WOT. I want to get the smart tabs though I'm not sure what size and also I'm sure I need another prop for what I use it for ( fishing locally with two/three people and a some gear) Any help would be appreciated,thankyou.

Skyhawk · Nov 6, 2008

Re: Prop causes motor to rev high.

Whats the engine?

You really need to know the wot operating range, and have a working tach.

frankie g · Nov 6, 2008

Re: Prop causes motor to rev high.

gotta have more info...size engine/type WOT spec's. sounds like to little prop, most likely need a bigger wheel, but ya have to know rpm max on your motor, that's a start, then we can go from there. once you have compiled enough info if you want top notch info, you get in touch w/ Ken @ prop gods,
i don't think there's anyone more knowledgeable then him, and has decent pricing also w/ swap out options.

Dhadley · Nov 6, 2008

Re: Prop causes motor to rev high.

There was no 1988 115 but we'll assume it's a V4 crossflow of about that era. Without knowing the top rpm with an average load we'd be shooting in the dark as fas as a prop recomendation goes.

If your motor is from about that era it's possible it has a water cooled regulator / rectifier. If the reg / rec has shorted out and that's why the tach doesn't work you'll want to correct that ASAP. If it is shorted internally it's possible that the wiring could catch on fire.

If you'll post the model number we can tell exactly what you have.

steelespike · Nov 6, 2008

Re: Prop causes motor to rev high.

I would think a 15" pitch is in the ball park on that size boat.
As suggested we need the present max rpm and speed.From your description
you might need more pitch but shouldn't make any changes without the specs.That motor will use about 11 GPH (gallons per hour) at WOT(wide open throttle)

bowman316 · Nov 6, 2008

Re: Prop causes motor to rev high.

to me 15 sounds way too small. I think you would want around 19. I have a 15 on my 70 hp evinrude, and that is almost not enough pitch for my 16 ft boat. Even without a tach, you can prob stand to go up a few inches in pitch, since your shot shot is great.
higher pitch saves more gas, since you are lowering rpm,s but not speed.

Dhadley · Nov 6, 2008

Re: Prop causes motor to rev high.

Without an accurate tach reading it's all a guess. If you run the slip numbers backwards, a 15 may indeed be close. Especially on a 2000 lb boat with no trim and it's a fairly safe bet the motor is mounted all the way down. Plus we don't know the actual condition of the prop either. Or what it's made of but it's probably aluminum.

evilwind1 · Nov 6, 2008

Re: Prop causes motor to rev high.

Thanks for all the replies, here is more specific info . The model # is E90MLCRD (does this mean it's a 90hp?) Operating range 4500-5500 rpm.....BIA 90 H.P. at 5000 rpm. OMC Waukegan Ill. The cover says 115 Vro v4. Ill try to post some pics of boat , by the way paid $500.00 for boat, motor and trailer , DF and all accessories. Thanks you all for help, Bill.

steelespike · Nov 6, 2008

Re: Prop causes motor to rev high.

evilwind1 said:
Thanks for all the replies, here is more specific info . The model # is E90MLCRD (does this mean it's a 90hp?) Operating range 4500-5500 rpm.....BIA 90 H.P. at 5000 rpm. OMC Waukegan Ill. The cover says 115 Vro v4. Ill try to post some pics of boat , by the way paid $500.00 for boat, motor and trailer , DF and all accessories. Thanks you all for help, Bill.

Yup a 90.If the prop is indeed a 15 it would be even closer to the right one.
35-38 is a respectable speed for a 19 with a 90hp.GPS speed is more accurate.
Get your tach working. With your exceptional hole shot you may be able to increase pitch but don't do it without a tach.Your better of if your slightly under propped because you can back off a little and still use it without damaging the motor.If you end up over propped you shouldn't use it except well below planing speeds or you could end up with a premature motor failure.

Dhadley · Nov 6, 2008

Re: Prop causes motor to rev high.

Yes, that's a 1984 90 hp V4 crossflow. Sounds like you got a good deal!

NelsonQ · Nov 6, 2008

Re: Prop causes motor to rev high.

evilwind1 said:
... by the way paid $500.00 for boat, motor and trailer , DF and all accessories. Thanks you all for help, Bill.

That a fantastic deal. I assume the seller didn't take long selling that one.

evilwind1 · Nov 6, 2008

Re: Prop causes motor to rev high.

Thanks again guys for all your help! I'm takin some riibbing from co workers about not knowing the motor is a 90 and not a 115. But like I said it was a great deal and ran/runs great and couldn't pass it up. I have a local guy, Long Island Propellers here and I'm gonna see what hes got. And the smart tabs I think will help out alot. I would like to keep fishing into December so I want everything to be right. Thanks again Bill.

Silvertip · Nov 6, 2008

Re: Prop causes motor to rev high.

Smart Tabs may not be needed unless there is a handling or porpoising issue you can't solve by other means. No sense spending money you don't have to.

Dhadley · Nov 7, 2008

Re: Prop causes motor to rev high.

Yep. Don't put the cart before the horse. Get the tach working.

bowman316 · Nov 7, 2008

Re: Prop causes motor to rev high.

i thought smart tabs were only for i/o motors?
he dosn't have power trim anyway.

Dhadley · Nov 7, 2008

Re: Prop causes motor to rev high.

You can use Smart Tabs on an outboard boat, they work well in most cases. The tabs go on the boat, not the motor. The fact that he doesn't have trim (it may be there and not working) makes it even more critical that we get the tach working.

Prop causes motor to rev high.

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