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Johnson V4 90 amp 115 whatbs the difference

G

gone_postal

Regular Contributor
"Okay, I had my '98 90hp r

"Okay, I had my '98 90hp rebuilt recently and all is well. I honestly didn't know much about the motor at the time though, but after some time here on the boards and also browsing the parts catalog, I've come to realize that the 90 is just a detuned 115.

The only part that I could spot during my quick skimming of the parts catalog that is different are the heads. Can anyone name anything else? Is that REALLY all there is to it? I imagine there might be some carb tweaks (different jets? or would they just need some adjusting?), but I'm sure my mechanic is capable of that. I'd love the extra hp just for the sake of having the extra hp - why not right?

Anyway, new heads are pricey, but I know the heads on these are very stout, so I would probably look for used. Hell, I actually have a spare set of 90hp ones in my garage right now. What is the difference? Are 115's shaved for higher compression? Is there anyway to mod 90hp heads into 115 ones?"
 
"Andrew, any number of motors

"Andrew, any number of motors share the same block so technically you may be able to turn an 85 horse into a 140 - but the cost is usually not worth it.

Aside from what you note I think you will find the carbs are different (or at least the jets depending on the exact model) and the throttle bodies as well.

So if you did spend the money and the time to make the changes, what would you get?

On a very calm day, on water that is like glass, you could jam down the throttle and you would see a whopping 2 more mph at wide open - maybe 3 if there was a gust of a tail wind.

So you really have to ask yourself before you even consider tyring to hop up a motor - how much am I willing to pay for each mph????

And if you live in the US, you would have to do all the work yourself. EPA regs make it illegal to alter the horsepower of an outboard motor from what it was sold as. So you will not find a reputable shop that would undertake the work for you..."
 
"Well, carbs are listed as the

"Well, carbs are listed as the same - would have to delve deeper to find out about jets, throttle bodies, etc.

I honestly expected more than 2mph though. I realize it's not proportional - that a 25% increase in hp wouldn't get me 25% faster, but figured I could see a 6-7 mph increase (which would be about 15% - I guess too optimistic).

As for cost, I have a ton of 90hp parts in a box in my garage. The previous owner's friend had the same exact 90 and threw a rod, so they tore down his motor and boxed up all the good stuff. I have heads, carbs, stator, all elec, etc, etc. I think I could easily offset the "upgrade" cost by selling my stuff on Ebay - now, whether or not it's worth it.....

I appreciate the input though! Just the kinda stuff I was hoping to find out"
 
"Okay, this idea is still real

"Okay, this idea is still really intriguing me.
According to the parts list on this website, the carbs, throttle bodies, entire rotating assembly, etc is identical. Honestly, the only differing parts I can find are the heads which I'm sure are a higher compression. I'm still convinced that some jetting would be different and my mechanic said high speed jets, etc could probably be drilled out if I find exact specs. (He didn't know about intake/exhaust ports either, but if carbs & throttle are identical, i can only assume exhaust is too)

So, I checked my SELOC and it's useless. I really want an OEM manual and if it would have the specs, this would put me over the edge to order it. Do OEM manuals list technical jetting specs?
The SELOC's carb rebuild section is very generic. Basically "remove this, remove that. Clean. Reinstall reverse of removal"."
 
"So, I checked my SELOC and it

"So, I checked my SELOC and it's useless---this--is the norm,except for the beginer..then,they r ok."
 
"jwbmarine -
Would and OEM m

"jwbmarine -
Would and OEM manual give jetting specs? The way it seems to me, if the carbs truly are identical, then there must differing adjustments and I'm curious to know if the OEM would state for a 90, do this, for a 115, do that."
 
If not mistaken the OEM worksh

If not mistaken the OEM workshop manual has a table giving the different jet sizes and types with reference to part numbers.
 
High speed jet in the float bowls are different. 90hp has 53d and 115 has 73d. (Both unavailable) Unfortunately, previous owner changed the float bowls on my 115 with ones from a 90 and didn't change the jets. Took me forever to figure out why it wouldn't run.
 
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