Differences between 20 and 25's??

[Instigator]

I've got a '73 20 hp that I put a 25 hp carburetor on that runs perfect.

I just stumbled on a '81 25 hp w/good compression but ugly.
Trying to see if theres anything on the '81 making it worth swapping w/the '73??

Powerheads appear very similar but the '81 has angled plugs where the '73'2 are straight.
Both have compression in the 150 range.

The '81's power is rated at 5000 RPM and I think the '73 is only at 4500 but is rubbed off the tag.

I checked the BRP parts site and see the blocks, heads and intakes are different but thats all I know.

Anyone know these better than me??

Ill check the AOMCI club next.

Thanks guys.

Gary

[olboatman]

Gary if you have the motors I think you have the blocks look alike but look at the transfer covers... the 81s are most likely way bigger. If that is the case the 81 is a 31.8 ci motor and the 73 is a 22 ci motor. Nothing is interchangable except the carb. Even the bolt pattern on the pull starter are different( mine are at least). The 81 31.8 ci can be made into a 35hp with a carb and timing change! Can you post some pics of the powerheads? Gary

[olboatman]

I lied..... the transom clamps and the LU may be the same( could be different spline drive shafts but just pull them out and swap'em) and the pans could be alike so cowls may swap. Gary

[Instigator]

Thx Gary

The antique site confirms its a 35 w/a 25 HPs carb.
The prop shaft is splined Vs pinned on the 25. After a yr of collecting props ��

I need to ck weight as it feels a ton heavier, but was electric start.
Its going on my dinghy that hangs on Davis that I can't overload.

You may also be interested that after a season of trying to make the inflatable run like it should, I just ordered a set of plans for the Glen L Squirt.
Says 120 lbs but I'll build w/no deck and all spruce so maybe a bit lighter.
Should be a rocket w/that 35 on there ��

[Instigator]

Gary if you have the motors I think you have the blocks look alike but look at the transfer covers... the 81s are most likely way bigger. If that is the case the 81 is a 31.8 ci motor and the 73 is a 22 ci motor. Nothing is interchangable except the carb. Even the bolt pattern on the pull starter are different( mine are at least). The 81 31.8 ci can be made into a 35hp with a carb and timing change! Can you post some pics of the powerheads? Gary
Finally getting around to putzing around w/this project.

Trying to decipher difference between the '81 25 hp that I have, and a '81 35 hp.
Thought it was only carburetor and found one on e-bay and the damn venturi is substantially smaller then the 25 hp.

Checked parts #'s on the brp site and verified that these pts are same, motor to motor:
Block, head, piston, intake, read plate and power pack.

Not sure where to go to get more inside poop??

This is pretty good but doesnt apply in my case.

http://forums.iboats.com/forum/engine-repair-and-maintenance/johnson-evinrude-outboards/545391-80-s-johnson-evinrude-25hp-to-30-35hp-conversion-with-pics

[olboatman]

Gary I have a carb on my 25 to 35hp conversion (1977) that came off a 89 I think with the primer(no choke plate) I will measure it this weekend and the 25 carb so you know the difference as it is torn down. You are correct that the other parts should have the same #s. BTW the 35 carbs are hard to come by as the APBA boys buy them up to convert the 25s. I looked for quite a while and ended up buying a seized powerhead for the carb. Gary

[powerabout]

Some years the 35 had different porting
They really went good like 77 78ish

[Instigator]

Gary, I bought a 35 carb and it's smaller than on the 25.

Powerabout, an '81 25 hp and 35 hp have the same block part #.

I know no history of this motor so is possible someone already installed a 25 carb.
Sucks not being able to find specs/differences.

[powerabout]

Check the years where they are different.
Plus in the middle of all that they went prop shaft rated