# more power out oa a 81' Evinrude 7.5?



## LeviStevenson (Apr 6, 2011)

Does anyone know of any possible ways that I could eek a little more power out of my 81' Evinrude 7.5? I just read a post where a guy put a 15 hp carb on a 9.9. Is this possible for me? Could I go to a 9.9? Also I'm not sure where to get a replacement prop or if that would even help. Any help on this matter would be greatly appreciated.


----------



## jellio5 (Apr 6, 2011)

I'm pretty sure you can't put a 15HP carb on a 7.5HP motor. Unfortunatly there's not much you can do to increase power on an outboard short of putting a different power head on it at which point you'd be spending as much as you would by selling your motor and upgrading. I would sell it and upgrade.


----------



## LeviStevenson (Apr 6, 2011)

could I go to a 9.9 carb? I knew the 15 would be out....but 9.9?


----------



## lckstckn2smknbrls (Apr 6, 2011)

You will have to find out what hp motors are based on that engine. 7.5 hp is probably the the most powerful of that group.


----------



## Bugpac (Apr 6, 2011)

If the 9.9 carb will work, let me know, I just got a 9.9 tonight that ill be doing the 15 carb swap on. I am not sure it will on the 7.5, i am guessing not.


----------



## LeviStevenson (Apr 6, 2011)

Do you know how I might go about finding out what engines were in that 7.5 group of evinrudes? I googled a bit but was pretty inconclusive. I'll try some more and post any findings...if any.


----------



## toddster88 (Apr 6, 2011)

How big a boat do you have the 7.5 on? Ive just acquired the same motor, just a year older, and they sure are great running little motors. Ive been trying to do some research on them as well with little luck. I think this is because the only made this style 7.5 from 1980 to about 1983. Im pretty sure theyre in the same group as the 4.5hp of the same years, so Im not sure about swapping parts n such, but Id like to know more too. Dont quote me though lol, I was just doin some research and narrowed down info I found from the site below.

https://www.boats.net/parts/search/BRP/EVINRUDE/parts.html

Ever consider a hydrofoil or something along thoselines?


----------



## Whoopbass (Apr 7, 2011)

A 9.9 carb will not work on your motor. There really isn't much you can do to it to get any more hp out of it.


----------



## Pappy (Apr 7, 2011)

That family of engines maxed out at 8hp later on. Don't think there is any difference between the 7.5 and 8hp carbs that would make you feel a difference in performance. I would stay away from modifications on that engine and look to replace with a 9.9 or larger and sell the unmodified 7.5hp to recoup some of the difference in money. The lightweight two stroke engines in decent shape are becoming harder and harder to find so start early!


----------



## LeviStevenson (Apr 7, 2011)

I have the motor on a 12' jon. Used to be more than enough motor..25 mph! I modded with some decking and such, all aluminum so not too much weight. Still does great with just me in it, but add a fishing partner and thats a whole nother story. Engine runs great, no complaints with the motor. I'm thinkin I may just go to a 9.9, or stick my to original plan of having my boat a solo machine....a 9.9 would still be cool though. Anybody wanna trade plus cash? Or just gimme a screamin deal on a 9.9? Thankyou everyone for your responses, I appreciate the help.


----------



## Outdoorsman (Apr 7, 2011)

Maybe try a different pitch prop...???

Outdoorsman...


----------



## LeviStevenson (Apr 7, 2011)

After extensive searching I have not been able to find anywhere to get a replacement prop for this motor. If anyone knows....lemme know. I can find them for 9.9 and up but not for my 7.5.


----------



## benjineer (Apr 8, 2011)

LeviStevenson said:


> After extensive searching I have not been able to find anywhere to get a replacement prop for this motor. If anyone knows....lemme know. I can find them for 9.9 and up but not for my 7.5.



You can buy one direct from evinrude. Looked it up on parts diagrams. It is PN 0390237. It is $89. Go here.
https://shop2.evinrude.com/Index.aspx?s1=9vv0gtqlc9533demg4frno8b47&catalog_id=0&siteid=1

That is the stock prop that came on it though, so it won't help unless yours is worn out or banged up.

Michigan Wheel sells a part that is an exact replacement also. It is going to be part # 012032. That is all they sell for that motor. It is a 9 pitch prop. That's probably going to be the only option. 

25mph in a 12' boat sounds pretty good to me. It might help to move your buddy closer to the back especially if he's sitting on the very front.


----------



## LeviStevenson (Apr 8, 2011)

Thanks benjineer, really appreciate the help. My prop is pretty banged up I think a replacement would help. I had originally built this boat for solo purposes...I think I'm gonna stick to that. I think I may try to acquire a new boat by seasons end....most likely a 14-17' at very least 48" wide. And probaly work on getting a 25-40 horse.....maybe jet....we'll see. If anyone wants to get rid of a tin by the end of the season lemme know...no mods please...I have the fever.


----------



## Pappy (Apr 8, 2011)

LeviStevenson said:


> I have the motor on a 12' jon. Used to be more than enough motor..25 mph! I modded with some decking and such, all aluminum so not too much weight. Still does great with just me in it, but add a fishing partner and thats a whole nother story. Engine runs great, no complaints with the motor. I'm thinkin I may just go to a 9.9, or stick my to original plan of having my boat a solo machine....a 9.9 would still be cool though. Anybody wanna trade plus cash? Or just gimme a screamin deal on a 9.9? Thankyou everyone for your responses, I appreciate the help.



If you have a stock 7.5 that runs 25mph then you have the fastest 7.5hp in the Universe.................


----------



## LeviStevenson (Apr 9, 2011)

The lake that I fish usually has a very swift river running into it. The time that I gps'd 25 mph I had gone about a mile up into the river and clocked that running downstream....if I kill the motor and just float it its about 7mph. So the 25mph was under ideal conditions going with the swiftness of a narrow river. The boat used to be incredibly light....possibly was lighter or around the same weight as the motor. Used to be around 17mph average on glass water with just me, law required items, one pole and light tackle, and lunch with a couple tall boys. Since mods with same gear I am running about 14 I would guess...haven't confirmed. So yeah...my 25mph claim is seemingly unreal....but as said, it has done it under special circumstances. But also, as said, this motor is a runner. I have beefed the boat up way more than necessary...if I were more safety minded I would have never put that 7.5 on the boat before mods. I think the boat in stock form would have best been suited with a 4hp....probably would have planed with that as well. I wouldn't be afraid to go as high as a 9.9 since reinforcement and structural modifications. The boat used to feel like a dented soda can running down choppy water....no it feels very soild...probably more solid than I should have made it. So yes pappy, if it were a flat running 25mph it would be the fastest 7.5hp.


----------



## acabtp (Apr 17, 2011)

LeviStevenson said:


> The lake that I fish usually has a very swift river running into it. The time that I gps'd 25 mph I had gone about a mile up into the river and clocked that running downstream....if I kill the motor and just float it its about 7mph. So the 25mph was under ideal conditions going with the swiftness of a narrow river. The boat used to be incredibly light....possibly was lighter or around the same weight as the motor. Used to be around 17mph average on glass water with just me, law required items, one pole and light tackle, and lunch with a couple tall boys. Since mods with same gear I am running about 14 I would guess...haven't confirmed. So yeah...my 25mph claim is seemingly unreal....but as said, it has done it under special circumstances. But also, as said, this motor is a runner. I have beefed the boat up way more than necessary...if I were more safety minded I would have never put that 7.5 on the boat before mods. I think the boat in stock form would have best been suited with a 4hp....probably would have planed with that as well. I wouldn't be afraid to go as high as a 9.9 since reinforcement and structural modifications. The boat used to feel like a dented soda can running down choppy water....no it feels very soild...probably more solid than I should have made it. So yes pappy, if it were a flat running 25mph it would be the fastest 7.5hp.


pfft, that is nothing. my jon w/ a 9.9 will go 100 mph... if i dropped it out an airplane. anything but flat running speed is misleading.


----------



## LeviStevenson (Apr 18, 2011)

Yeah well everyones a critic. Just stated what it has done....and I was impressed. It goes 65 to 75 mph on the way to the lake if ya really wanna split hairs.


----------



## jellio5 (Apr 19, 2011)

There's always the visual horsepower option.....put some flames on that baby you'll gain at least 3HP. :lol:


----------



## LeviStevenson (May 27, 2011)

Ok I found the solution....traded it for a trailer. Then my father in law gave me an older johnnyrude 9.5 runs great after a little tinkering. I will take my gps tomorrow and let you guys know if it was an improvement or not. I just got 15 mph outta the 7.5 in chop against 15 mph winds....she was trying to impress me on the final ride.....I just might miss that 7.5.......we'll see.


----------

