9.9/15 evinrude carburetor difference

[rasteele]

I have a9.9 evinrude that I wouldn't mind having a15 hp carb on it to make it a15, it has a15 hp high speed jet in it now, waiting on the true 9.9 jet so that it will run right. Now, just thinking. Since the only difference between the 9.9 and 15 is the carb is the throat and I already have the 15 jet, can I hone out the throat so that it can accept the extra fuel just like the 15 hp

 

[gm280]

Seem this type question surfaces on here from time to time. I suspect the real difference between a 9.9 HP and 15 HP engine is its ability for the 15 HP version to turn higher RPMs. Especially if the displacements are the same as well as the engine itself. So a carb being the only change (or so it may seem) allowing a little more fuel/air to pass through is the answer. However, with that stated, it would be hard to seriously tell the difference, if any, in top end performance. Changing the high speed jet only changes the fuel air ratio and not increasing the CFMs being passed. So I would suspect the carb venturi is slightly larger in the 15 HP version. But unless there are different parts numbers for the two carbs, I can't see any other difference... Just remember, polishing any opening even slightly makes a huge change in the volume it can pass. In other words, it take a very little in diameter to make a substantial difference. But you also want to keep the fuel draw up as high as possible to pull the fuel. And that some times sadly means low end idle can be iffy. JMHO!

 

[kbait]

Google 'leeroy's ramblings', and navigate to 9.9/15hp section. Read the carb section, and you'll know all there is to know!

 

[tomhath]

I have a 9.9 Johnson with the original carb and a 9.9 Evinrude with the 15hp carb. As far as pushing the boat, the difference is hardly noticeable. You get a few more RPMs when it's wide open, but anything less than wide open there's obviously no difference in power since the throat is throttled.

 

[rasteele]

I'm an reader of leeroys's and I have read the part about you can not put a 15 jet in a 9.9. I was just wondering if anyone has tried to make the throat bigger to compensate

 

[racerone]

There is more to a carburetor than just making the throat bigger.----There is a portion in the bore of a carburetor that is smaller in diameter and properly shaped.---It is called a " venturi "--and it is then not a simple matter of opening the throat up !

 

[F_R]

Air flow through that venturi is what causes a low pressure area, which is what draws the fuel up from the bowl & jet. Let's just say the engineers are getting paid to know what they know about venturis. Back yard hot rodders have been experimenting with them for 100 years. Some win eventually, some lose mostly.

About the RPM: It doesn't have more horsepower because it turns faster, it turns faster because it has more horsepower. More horsepower lets it turn the same prop faster (and engine RPM.) Turning the prop faster makes the boat go faster. How much difference in the seat of the pants feel depends on many factors, boat, load, etc. One thing for sure, it won't go 50% faster. At least not unless the 9.9 isn't enough to plane the boat, but 15 is.

 

[raczekp1]

1. 15 hp has bigger carb throath{ventuti part}
2. 15 hp has spacers under leaf valve stop in inteke part of powerhead
3 .some 15 hp has bigger exhoust hole

 

[raczekp1]

1. 15 hp has bigger carb throath{ventuti part}
2. 15 hp has spacers under leaf valve stop in inteke part of powerhead
3 .some 15 hp has bigger exhoust hole

 

[bwkre]

I think everyone who has ever owned an older 9.9 has considered converting it to a 15. I did too! Some models require few parts to be changed and some models require more. Finding the parts can be a challenge. I like my 9.9 and decided to leave well enough alone, and it runs great. Instead I picked up an 18 hp for $250. When I'm not on a lake with a 10 hp max, I use the 18. A lot more power, but not double the speed.

 

[rasteele]

Thanks for the replies. I kinda feel like I got slapped in the face lol but it's all good

 

[rasteele]

And,FR, the boat planes off fine, actually scares the wife . It's just hard not to tinker with it like I used to do with my old cars, man I loved that 69 nova, lol. I'm gonna leave it alone, be happy with it. Thanks for the advice