What's the difference...

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  #1  
Old 05-10-10, 12:29 PM
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What's the difference...

Between a Johnson 120TLARK and a 140TLARK? I see different carburetors, but everything else appears to be the same.. Could someone swap the necessary 140 parts to a 120 and get the extra 20hp from it?
 
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Old 05-10-10, 08:34 PM
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I'm not sure what the differences are, I've never modded a omc. I think the port timing is the same so it could be carbs and timing.
 
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Old 05-10-10, 09:17 PM
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Originally Posted by samuari View Post
I'm not sure what the differences are, I've never modded a omc. I think the port timing is the same so it could be carbs and timing.
What would be different on the timing? Hard parts or simple adjustments? I'm merely curious.. I figured since they're virtually the same engine but a difference of 20hp, I'd be willing to (once the engine runs the way its supposed to anyway) maybe "tweak" it a little bit. I'd love to see 45mph with the trolling motor and batteries in it.. (45mph with just me and no troller or batteries. 40-42 w/ that stuff on-board.)
 
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Old 05-11-10, 03:48 AM
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The only difference between the 170 and 190 mid/late 80's Mercruisers were the 4bbl carb instead of 2bbl and some heavier valve springs. Since it would be extremely difficult to replace valve springs on a 2-stroke outboard, I'd say it's the carb.

Oh ... and 50:1 instead of 35:1.
 
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Old 05-11-10, 06:41 PM
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Originally Posted by Rick Johnston View Post
The only difference between the 170 and 190 mid/late 80's Mercruisers were the 4bbl carb instead of 2bbl and some heavier valve springs. Since it would be extremely difficult to replace valve springs on a 2-stroke outboard, I'd say it's the carb.

Oh ... and 50:1 instead of 35:1.
I might have to round up some carb main bodies later this year... I've never modified an outboard either, so I might try it.. Of course, I gotta get it running A.O.K first.

35:1 is way too freakin' expensive.. I'm hoping by the end of the weekend I'll get it running on a cool 50:1.. 60:1 at idle would be miraculous. I need a pressure tester... know where I could find one? (I asked this in the other thread I got going, I know..)

edit: From the parts explosions, the only differences in carbs between the two engines is the Idle air bleed orifice, High speed Orifice, and Intermediate Orifice. That's IT.
 

Last edited by Legal v8; 05-11-10 at 07:19 PM.
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