1992 Evinrude 9.9 2 stroke running rich with early 1987 15hp carb

[DeanHensler]

I took my 92 evinrude 9.9hp 2 stroke and put a 15hp carb from an early 1987 15hp evinrude on it. I'm not getting any more RPM than I was with the 9.9. It feels like it's running too rich at full throttle. Sure enough I removed a spark plug and it's wet. Is there any way to lean out the 15hp carb under full throttle? The motor starts and runs just fine in the low RPM range, I'm just not getting the higher RPM I expected, likely because it's running too rich.

 

[jimmbo]

Another attempt to turn a 9.9 in to a 15. The fact that more air in requires more exhaust to get out, Some 15s are different than the 9.9s on the exhaust side. Some 15s have a slightly different reed/induction system too. But that has been posted to death many times in the forums

Before you go messing with a carbs calibration, besides there aren't jet kits available for these things, do some basic checks. Float condition and setting, Inlet valve and seat. Missing main jet.

 

[racerone]

I think I might design a 25 HP carburetor to put on these 9.9 models.-----Likely sell really well on that " fleabay " site.

 

[flyingscott]

What did you expect to happen? The 9.9/15 motors were virtually identical in 1992. You picked up 200 rpm so obviously the motor is making more power. If you want more power buy a bigger motor.

 

[DeanHensler]

What did you expect to happen? The 9.9/15 motors were virtually identical in 1992. You picked up 200 rpm so obviously the motor is making more power. If you want more power buy a bigger motor.

This was absolutely no help. I did a ton of research on this before changing carbs. The 1992 9.9 has the same exhaust as the 1987 15hp. This should have given a substantial performance increase. There is an issue here with the motor is running rich.

 

[flyingscott]

I have owned several of those motors, and the difference between a 9.9/15 is NEVER as big as people think. There was never a substantial power difference between those motors. But good luck with your motor!

 

[jimmbo]

Part of the lack of 'Substantial' differences in power are partially due to the 9.9 being under rated, so as to sneak under a lot of '10HP and more' Regulations. It probably was closer to 11 or 12 hp(mercury, when it added 'zeros' to the HP of a motor, called its 9.8 a 110), and then it was only a 3 HP difference. Allow for the Tolerances allowed, an engine just shy of 14hp could be called a 15. In reality, a 50% increase in HP from a 9.9 hp really can't happen by raising the WOT range by 1000 rpm, 1500 in some later engines.

That should rile a few of the Posters who will be saying they stuck a 15 carb on a 9.9 and their boat went from 18mph to 30 mph. blah blah blah...

 

[kbait]

Sounds like your new carb may be a 9.9 carb body with a 15hp main jet. That can’t work..not enough air at higher than idle throttle setting.
Look though the carb bores of both carbs.. is the ‘15’ carb bore diameter substantially larger?

 

[Tim Frank]

Sounds like your new carb may be a 9.9 carb body with a 15hp main jet. That can’t work..not enough air at higher than idle throttle setting.
Look though the carb bores of both carbs.. is the ‘15’ carb bore diameter substantially larger?

Deja vu....
There was a thread a few years ago in here where this guy had a hair-tearing time because a previous owner had messed with the OEM carb on a 9.9 HP and rejetted it.. After a lot of anguish and help from forum folks he sorted out the cause and solved it.
Sound familiar?

Dean, I have to say, of all the posters/owners in here, I would have thought you would have been the last to go chasing the holy grail of major performance boosts from minor tweaks. Your previous adventure should have given you pause.
Bottom line here is that if you really think you can out-design the original engineers, do some searches on the topic in here and read the litany of failures. The archives are full

Preaching over....

 

[DeanHensler]

Sounds like your new carb may be a 9.9 carb body with a 15hp main jet. That can’t work..not enough air at higher than idle throttle setting.
Look though the carb bores of both carbs.. is the ‘15’ carb bore diameter substantially larger?

Yes. I checked this first thing. It is for sure a 15hp carb. Much larger than the 9.9

 

[DeanHensler]

Deja vu....
There was a thread a few years ago in here where this guy had a hair-tearing time because a previous owner had messed with the OEM carb on a 9.9 HP and rejetted it.. After a lot of anguish and help from forum folks he sorted out the cause and solved it.
Sound familiar?

Dean, I have to say, of all the posters/owners in here, I would have thought you would have been the last to go chasing the holy grail of major performance boosts from minor tweaks. Your previous adventure should have given you pause.
Bottom line here is that if you really think you can out-design the original engineers, do some searches on the topic in here and read the litany of failures. The archives are full

Preaching over....

So basically you're saying putting a 15hp carb on a 9.9 motor isn't going to make it produce more power. I don't understand why the thousands of attempts and some success stories of this in the past. If it just flat out doesn't work why hasn't isn't that widely known by now?

 

[racerone]

Fact.------Run a test with a " test prop " and tachometer on this 9.9.-----Install the 15 hp carburetor and test again.----Or a shop that has a dynamometer to determine actual power.-------Guessing does not work.-----You are aware that in 1993 they redesigned these wonderful motors .----More displacement.

 

[Tim Frank]

So basically you're saying putting a 15hp carb on a 9.9 motor isn't going to make it produce more power. I don't understand why the thousands of attempts and some success stories of this in the past. If it just flat out doesn't work why hasn't isn't that widely known by now?

What you may need is one of those miracle carburetors that can get 200 miles per gallon as a straight retrofit but apparently were all bought by the big oil companies and sit on a shelf in a warehouse somewhere....probably in Roswell.

Seriously, I am not saying it cannot be done, but I have never seen a definitive response to the questions, just lots of guesses. The parts list required is far more than just a carb (or a jet ) Once you start transcending model years, and carb subtleties, the variables in the equation will defeat most ....if there is in fact a solution.
There are innumerable posts about guys (and gals) who have tried but performance sucks. "Some top-end gain, but below 2000 RPM it sucks" ...."hard to start and bogs at WOT"...."someone told me that I could just put a 15 HP carb on my 9,9 HP and it would be a 15HP but now it runs crappy. Why?".....etc
If you were to go through EVERY part in the list for your 1992 9.9 HP and compare it line by line with a 15 hp from the same year you might be able to catch ALL variances, but there is no app for that as far as I know....would be really tedious.

Last I heard your 9.9 was on a 20+ foot pontoon but you were OK with performance since you were on a small lake.
Something change?

The million dollar takeaway for you should be the post that said essentially "if you want more, buy more". Great advice and IMO will save you enough time to be worth the price; unless you place a low value on your time.

Good luck and hope you get somewhere with this, and I hope you do not pass on the problems to the next owner; you know how aggravating that can be.

 

[racerone]

As stated marketing comes into the picture.-------It is easy , perhaps legal to put 9.9 decals on motors. one day and 15 HP on basically the same motor the next day.----Economy of scale in manufacturing too.-----They put stuff in the showroom that folks will carry out of the showroom.

 

[kbait]

I have successfully boosted several 9.9 motors with 15 carb’s and they all ran fine. I swapped an ‘83’s carb only..same 9.9 reeds (no spacer) and square exhaust tuner.. idled fine and increased top end from 17 to 20 mph. ‘92 carb swap should work as it’s basically the same powerhead ‘74-‘92..(‘93’s and newer are a different animal). If carb body is actually a 15, perhaps someone reamed out the main jet? Faulty float valve? Link/sync way off?

 

[jimmbo]

If the motor was on a very light hull, you would see more of a difference. On a Barge, or big Pontoon, the difference between a 9.9 and 15 are not going to be substantial, probably less than 1 mph

 

[flyingscott]

Highly unlikely any difference at all. A 15 hp vs a 9.9 on my ss160 is negligible at best but the 9.9 is a better runner at an idle.

 

[scout-j-m]

FWIW I have a 1992 9.9 as well with a plastic topped 15 hp carb. I also have a 1982 9.9 and 15hp model. In troubleshooting the 1982 15hp I swapped the carbs Between the two 1982 models and while at it placed it on the 1992 model. It turned a few hundred less rpms and had less holeshot. This was done on the same hull, same load, same prop so the carb was the only variable. Now I can’t say for sure the 1982 15hp carb had the correct jet or didn’t have some other issue but it was a noticeable difference.

 

[DeanHensler]

What you may need is one of those miracle carburetors that can get 200 miles per gallon as a straight retrofit but apparently were all bought by the big oil companies and sit on a shelf in a warehouse somewhere....probably in Roswell.

Seriously, I am not saying it cannot be done, but I have never seen a definitive response to the questions, just lots of guesses. The parts list required is far more than just a carb (or a jet ) Once you start transcending model years, and carb subtleties, the variables in the equation will defeat most ....if there is in fact a solution.
There are innumerable posts about guys (and gals) who have tried but performance sucks. "Some top-end gain, but below 2000 RPM it sucks" ...."hard to start and bogs at WOT"...."someone told me that I could just put a 15 HP carb on my 9,9 HP and it would be a 15HP but now it runs crappy. Why?".....etc
If you were to go through EVERY part in the list for your 1992 9.9 HP and compare it line by line with a 15 hp from the same year you might be able to catch ALL variances, but there is no app for that as far as I know....would be really tedious.

Last I heard your 9.9 was on a 20+ foot pontoon but you were OK with performance since you were on a small lake.
Something change?

The million dollar takeaway for you should be the post that said essentially "if you want more, buy more". Great advice and IMO will save you enough time to be worth the price; unless you place a low value on your time.

Good luck and hope you get somewhere with this, and I hope you do not pass on the problems to the next owner; you know how aggravating that can be.

Yes this is on a 24' pontoon. Bottom line is I'm mechinically inclined and I like to tinker with stuff. I still have my 9.9 carb and it can go back on the motor at any time. I can put the 15hp carb back on the 15hp motor (which is a tiller, short shaft so I can't put that on my pontoon) and sell it if this doesn't work out. No big deal. I would NEVER sell something with a known issue to someone else without disclosing it. That doesn't even play a factor in this situation. I'm just tinkering here for fun.

 

[DeanHensler]

I'm not broke down on the side of the road here. This motor is running and I have the backup plan to put the 9.9 carb back on if needed. In the spirit of tinkering with stuff, which is literally what I'm doing, let's try and see what we can come up with here.

From all of the research I did, the only difference between the 1992 9.9hp and the 1992 15hp should have been the carbs. Maybe this isn't true but I sure believed it to be. The 1987 15hp motor I bought was the closest thing I could find so that's what I've got. This motor feels like it "wants" to really take off at about 4500 RPM but above that it starts to gargle and I'm sure it's running too rich as the plugs are wet. I really believe if I can lean it out a little bit it'll go past 7000 RPM. It will hit 6000 RPM with new plugs but once they get too wet then it won't go over 5500.

So maybe the jet is somehow to big in this carb?
Maybe the needle has some gunk on it and the float isn't able to close it?

It certainly sounds like the next logical step is a good cleaning and inspection of the 15hp carb.

If anyone else has been down this road I would appreciate any success stories they had.

For everyone else with useless comments like "buy a bigger motor", please understand I'm just having fun tinkering around here. I'm not broke down on the side of the road begging for a tow.