Interchangeable parts for '79 Evinrudes V4s

[CaneCutter79]

This is probably a dumb question but can you convert an 85hp V4 to a 100hp or 115hp V4 by simply changing the carb? I'm 99% sure the answer is no but the two motors are identical in size. I just confirmed the pistons are the same size between the two motors by looking up the part numbers between an 85 and a 115. I once had a guy tell me on smaller outboards, you could "upgrade" the power by switching carbs. While I think this is bunk mechanically, I just thought I'd ask the question.

I know these two motors have a lot of interchangeable parts so I am wondering, just how interchangeable can it get? (I know, depends on model no)

My 85hp is a 85995R

 

[emdsapmgr]

Re: Interchangeable parts for '79 Evinrudes V4s

Yes-within reason. The only difference between many of these engines are the carbs. Especially on the flatback V4 powerheads. Check the throat size which is cast into the front of each carb flange. Possible that you may have to rejet the mains slightly when putting larger hp carbs on the 85. (for instance you'd have a poor running engine if you put 140 carbs on the 85.) Too much fuel for the airflow. The 85 hp engine uses one block, the 100/115 use another, the 140 is completely different with the exhaust bubble on the back. Likely the 85 has different (low) porting.) The 115/140 hp powerheads also uses the rubber inake filler blocks which are good for 3-5 hp-they can be put on any V4. I got a set of big bore 1 5/16" 125 hp carbs to run on a 1972 small bore V4 100 hp block. Took me a lot of time re-jetting, but wound up with a great running engine. Picked up about 250 rpm, enough to go one prop size larger.

 

[CaneCutter79]

Re: Interchangeable parts for '79 Evinrudes V4s

So re-jetting sounds like work best done by a marine machine shop and for the money invested in an older motor, it's probably not worth the expense right? I could actually mess up the motor by trying to increase the power a bit. Without knowing the full history of these outboards in great detail, it's not an easy thing to do and could be risky right?

 

[emdsapmgr]

Re: Interchangeable parts for '79 Evinrudes V4s

Look at it another way. The 85 hp engine will perform comparably with a 100 or 115 from a dead stop holeshot to mid speed- till the engine gets into the higher rpm range. At 4500 or so, the higher hp engine will start to pull away from the 85.

 

[CaneCutter79]

Re: Interchangeable parts for '79 Evinrudes V4s

Yeah and that higher end is where I was wanting the boost too. Thanks for your help though. I think I'll stick to repairing my engine vs. repairing it and creating potential new issues as well.