18 or 25? Anyway to tell?

Bman2895

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So I recently acquired an old evirude. Supposedly a 25hp. The transom tag would indicate a 73 25hp. However the cowling is definitely the 60s-71 cowl. Not the square style of a 73. The welch plug is jacked up and illegible. So either it's a 73 with earlier cowling. Or an earlier motor with a later transom bracket/plate?

This motor externally has been through alot. Signs it maybe fell off the boat going down the road. Skegs a little bent with road rash. The shifter is broken off, and the pull start assembly isn't from this outboard it's off a Johnson. The top cowling doesn't match the bottom paint wise. So I'm thinking the motor hit the road and busted up the cowling, pull start, and broke the shifter lever? Maybe in all that the transom bracket was damaged and swapped hence the wrong plate?

Anyway other than the plug and transom plate. Is there anywhere else on the motor that would have the info? Or some other tell that would clue me into if it really is a 25. Or an 18 with parts off a 25.
 

racerone

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Any pictures?----Find / remove the high speed jet.-----What # is on it.
 

Bman2895

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I didn't think of that good idea. And I'll take some when Im home from work today. Photos of the power head?

I know it's got the bigger carb that started in 68-69? (Going off parts diagrams) But still has the coils on the timing plate. So pre 73?
 

Bman2895

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There is the plug but it's all banged up? Like it was replaced and hammered in very poorly. Can't read anything on it.

So what would I be looking for jet wise?
 

Bman2895

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Took the carb off. and I see the main jet but theres no numbers on it indicating size. Am I looking for something in particular?
 

racerone

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High speed jets have a number on them.----Are you sure you were looking at the high speed jet ??
 

racerone

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Way inside the float bowl.----Need to remove drain screw.---Then get it out and read the number.
 

jimmbo

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That Jet is used in the 25hp Carb

The differences between the 22 cubic Inch 18/20hp and the 25hp are:
1)Pistons - Relocation of the Wrist Pin, changes the Port Timing, and lowers Compression
2)Cylinder Head - Restores Compression
3)Intake Manifold - Required for the Larger Carb
4)Carb - Larger Bore and Venturi
5)Crankshaft - More precisely Balanced for the higher Rpms
 

jimmbo

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If those parts from a 25 are installed on an 18/20hp, the engine can be ruined.
Putting the 25hp Head on an 18/20hp, without changing the Pistons will result in too much Compression and Detonation will occur.
Putting the Carb and Intake for a 25 on an 18/20 without the Piston and Head Changes, will result in a Motor with poorer Throttle Response and may become a Chore to operate
Without the Crankshaft swapped, the Engine, may suffer from Vibrational Issues
 

racerone

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So you found a number as clearly stated there would be.----#72 was used on 25 HP models.
 

Bman2895

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Yeah that's 100% my bad I expected it to be on the end of the jet. It was on the side I was covering it with my fingers the whole time.

I'm fairly confident the heads never been changed. Just kind of going off context clues but paint matches perfectly there's no signs it's ever been off.

I thought the later years 68+ 18-20-25 all used the same carburetor body. Atleast that's what a parts diagram would indicate?
 

jimmbo

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When I look at the 1973 Parts Lists, I see different Part #s for the 18/20 and the 25hp Carbs


Pics of your Frankinrude, would be nice
 

Bman2895

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I'll get some good ones in the daylight tomorrow. It's likey not a 73 going off the ignition not having the coils on the block. It's 69-71 I'm thinking.
 

Bman2895

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I keep getting an error when attempting to upload. Says file could not be written to the server.
 

tphoyt

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The big yellow box at the top of this page may help you get some pics posted.
 

jimmbo

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The Cowl Cover looks like a 1969(based on the Graphic on the Back of the Cowl) . The Recoil looks like it was from a Johnson Motor. Maybe the Transom Bracket was replaced, or the entire Powerhead and Cowl were placed on a 73 Midsection.

It looks like some Sketchy Glass Repair on the Transom, in the 1st Pic
 
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