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G

gone_postal

Regular Contributor
"1998 Johnson 90hp - J90ELECM

"1998 Johnson 90hp - J90ELECM

Before anyone asks - YES, it's worth it to me for the 5mph I'd gain!! Can never be too fast....

Anyway, I want to convert this to a 115. After studying many parts fiches, the ONLY differing parts I can find are the heads. The carbs, throttle bodies, rotating assembly, ignition, etc are all the same part #s. Luckily I stumbled across a set of used 115 heads on Ebay and got them for cheap. I haven't compared them to my 90's yet, but I'm assuming they're shaved to result in higher compression.

Now, if this is the case, surely the motor would want more fuel right? No way a set of heads increases 25hp in a motor this small? Unless the 115 is overrated or the 90 is underrated. BUT, if the carb #s are the same, then wouldn't that mean the jets are the same too? I don't see jets available separately, so I can only assume they come preinstalled.

I have OEM service manual and it shows initial adjustments (as far as turns out, etc) being same between 90 & 115.

Any ideas? Is there any definitive place that I can find out for sure if the carbs differ at all? (or anything else for that matter)"
 
"This sounds a little fishy- 2

"This sounds a little fishy- 25 hp increase from cylinder heads??? Gotta have missed something in there some where. I would get both motor shop manuals and compare some procedures - We did put 105 head on a 120 chrysler with 140 carbs and reeds, but it would only run on Nitro. Got about 180 hp out of it.

Don't get me wrong- I love this stuff. Let us know what you find out??"
 
"William -
The OEM service m

"William -
The OEM service manual covers all 60* motors (90,100,105,115,150 & 175) - actually has pictures of 115s on the cover!! Anyway, I've read every page in that book (minus lower unit) and can't find a difference in there for settings (timing, adj needle, etc settings all the same).

As for the exploded diagrams, the list from a 90 carb and 115 are identical. The ONLY discrepancy that I see is this:

I know the carb has an adj idle needle, intermediate orifice & high speed orifice. All listings are the same, but BOTH the 90 & 115 have two listings for item #15 (which in diagram is lowest - ie - high speed orifice). The two listings are "Orifice Plug 73D (part #0327487)" and "Orifice Plug 58D (#0328543)".

Now, when I initially researched this, I printed out both motor's lists and checked off items on each one as they matched up. As I said, both lists turned out identical. I now realize though that there are too many orifices listed (there is an item #9 which is labeled as Orifice Plug #20, so I assume that mid speed - right location in picture at least).

Soooooo, are the part #s stamped on these? I'm gonna pull my high speed and look - if so, is it safe to say if I order the opposite one that it could be my potential holy grail? It at least makes sense - the increase of hp would be seen at top end, so a different high speed jet would be all that is needed right?"
 
"[b]UPDATE[/b]

Got home rig

"UPDATE

Got home right before last post and hadn't checked front porch yet - well, my 115 heads came in! I grabbed my micrometer and a spare set of 90 heads that I have and the 115's are 1/100th inch shaved. I also pulled the high speed jet and it is #58D. So, I can only guess that a 115 would have #73D which is numerically higher and hopefully flows more fuel. Is this all I would have to swap? I shouldn't have to drill anything out, etc right? I'm mechanically inclined and not afraid to jump into stuff, but haven't had much experience working w/ carbs. Thanks!!"
 
"[b]UPDATE....AGAIN[/b]

Wel

"UPDATE....AGAIN

Well, looks like I might be way off. The parts list and exploded diagram I was looking at was on another site (boats.net) b/c they actually have a diagram (unlike this site). That is also where I printed the parts list. I thought I had checked this site too, but apparently not. I was correct on high speed jet - 115 is 73D. Looks like mid speed is different and it gives different part numbers for throttle bodies AND carbs themselves. Not sure this is necessary though - might just be that the assemblies include the necessary jets. I'm hoping I can still get away w/ the upgrades jets, but I'm going to keep my eye on Ebay in the meantime for 115 assemblies"
 
good luck man. I have changed

good luck man. I have changed carbs to get more power...turned 9.9 into a 15. Does not surprise me you missed something tho....No such thing as "free" horsepower...well...except for when I take the air filter outta my pickup.
 
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