Convert 175hp Evinrude to 200hp, plus carb question

[Numlaar]

Hey all,

Num here again.... (sorry! )

OK since I will basically have the entire front of my motor apart, (1978 Evinrude 175hp) I figured it wouldn't be that much extra work to try and get a little more HP out of it...

After reading a number of posts regarding upping horsepower on similar models (same basic blocks), from what I can gather, it comes down to carburation and exhaust...

I did some extensive research last night, between the differences of a 175hp and a 200hp, and this is what I came up with:
Heads = Same
Pistons = Same
Exhaust plates (inner/outer) = Same
Leaf plates (reeds) = same

In fact everything but the carbs are the same... so these are my questions:

1. Regarding the carbs, there is an orifice in the upper carb body, and an orifice that goes into the bottom of the float bowl... I never did learn which is which (idle jet vs high speed jet).

2. Anyone know what the difference is between the carbs on a 175hp vs 200hp?
part #'s
Lower carb: 390022 (175hp) : 389410 (200hp)
middle carb: 390021 (175hp) : 389409 (200hp)
Upper carb: 390020 (175hp) : 389407 (200hp)

3. The upper orifice is not listed for any carbs but the 235hp models... are they different between the 175hp/200hp? and are they available/replaceable?

4. The lower orifices are different between the 175hp and 200hp:
325019 (175hp) 320661 (200hp)
Usually the site lists the jet size but doesnt in this case, so again what is the difference?

Just trying to see if my idea is feasible while I am swapping out the intakes for my shifting problem.

So anyone ever upped a 175hp to a 200hp, and if so, how do you do it?

 

[emdsapmgr]

Re: Convert 175hp Evinrude to 200hp, plus carb question

The 150/175 blocks are the same. The 200 is different. The 200 is ported like a 235, but does not have the bubble back exhaust. The high porting in the 200 affords it a higher max operating rpm than the 150/175, and that is where much of the hp difference is made up. You could square off your ports on the 175, effectively raising your port timing ever so slightly. Replace your heads with the high performance 1979 235 small bore heads. You'll pickup about 10 lbs compression. Your 175 does not use the 6 rubber intake filler blocks that are unique to the 200/235. I'd add them for a 5-8 hp increase even though they are NLA: 322722. These early 200 carbs are more like the 235 carbs than the 175 carbs. They have a unique pullover jet between the two venturis, which adds more fuel at top end. The 200 carbs are 1 5/16" throat size. The 235's are probably 1 3/8" diameter: the more air/fuel you get into the engine the more hp you will make. You can't just increase jet size without increasing the diameter of the carb throats too. With all those changes you might get close to 200 crankshaft hp.