Converting a Johnson 9.9 to a 15 hp

i was told that this could happen by changing the carburetion on the motor. <br /><br />can anyone give me informnation on this please? the 9.9 i have is a 74 year. and if this is possible where might i find the parts. id like to do this myself if possible.<br />Thak you

Re: Converting a Johnson 9.9 to a 15 hp

This topic has be covered-adnaueseum.<br /><br />Use the search function and get ready for a LONG read.

Re: Converting a Johnson 9.9 to a 15 hp

Post padding DJ....? <br /><br />On the old original 9.9's, all that was done was to change the carb. Later models added a shim to the reeds, a tuned exhaust tube.<br /><br />Beefing up a 9.9 to a 15 has mixed reactions by those who do. And for the age of your engine, I would think that the cost will be "prohibitive".<br /><br />Why do you want to beef it up?

Re: Converting a Johnson 9.9 to a 15 hp

DJ, i did use the search and must not have entered in the correct "Keywords".<br /><br />OBJ, i want a bigger Motor, i am on a research mission here. is it cheaper than buying a 15 or 20 hp motor? i wont know until i ask. <br />Thanks for your responses.

Re: Converting a Johnson 9.9 to a 15 hp

i used 9.9 to 15 ....got 43 matches using the search

Re: Converting a Johnson 9.9 to a 15 hp

Mo....I don't think you would be able to tell the difference beefing up your 9.9. Yes, it would be cheaper to "beef" up the 9.9 but I really think you'd be throwing money away...if you could find a carb. If you need more horses....look for a 20.

Re: Converting a Johnson 9.9 to a 15 hp

Must be May already.

Re: Converting a Johnson 9.9 to a 15 hp

diggerdan17 and fireman57, sorry to have insulted your intelligence and posted a question that has been asked and answered.<br /><br />i'll remember that while i use another forum.<br /><br />all others , thanks for the info. i'll se it somewhere.

Re: Converting a Johnson 9.9 to a 15 hp

That wasn't very nice , If you didn't want to help him , Why did you even post ?

Re: Converting a Johnson 9.9 to a 15 hp

Mo_Tick, go to this mans website he has it all!<br /><br />www.wisnersinc.com/Fishing%20Info/OMC/9.9%20OMC%20info.htm

Re: Converting a Johnson 9.9 to a 15 hp

thanks pierretheron, thats great info.

Re: Converting a Johnson 9.9 to a 15 hp

From that very good article above:<br /><br />Difference between the 9.9 & 15hp : When they designed this series of motors, they designed it as a 15 hp & then detuned it with a different carburetor for the 9.9. When the 9.9hp and 15hp came into being in 1974 and up thru 1978, the only real difference between the two motors was the carburetor. In 1979 they added a shim, part #325038, (one for each cylinder), behind the leaf valves & under the stop plate for the 15 hp, apparently to allow the motor to suck more fuel & air mixture in. <br /><br /> <br /><br />The outside visual dimensions of both carburetors appear the same, unless you look inside the throat. If you look in from the rear, you will have to position the throttle plate to a horizontal position to be able to see the throat very well. The 9.9 hp carburetor’s internal throat is .625 dia., 15 hp internal throat is .875 dia. up until late 1987 when they went to a plastic topped carburetor. The outlet or rear throat dia. is the same on both to match the manifold port dia. The idle jet venturi system is also slightly different between the two. The part number for the the pre 1987 9.9 hp Carburetor Assembly is #388936, while the 15 hp Carburetor Assembly is #338273. This increased dia. & larger main jet allowed it to breather better & pull more fuel in, increasing the RPM about 1000 RPM.

Re: Converting a Johnson 9.9 to a 15 hp

Mo,<br /><br />The 10 hp and less engines seem to sell for good $ on ebay while the larger seem to go cheap.<br /><br />Maybe try selling your 9.9 and find a good 20 or so.<br />Good Luck.

Re: Converting a Johnson 9.9 to a 15 hp

My apologies to Mo. Sincerely. Just a bad day. Scrapper, I wish I could take the words back. Just seems like everyone waits until the day before they want to use their boat. I've been a member for a long time and I don't think you have ever seen me dig at anybody until now. Just seems like the new posters thread by JB isn't read or used. I'll try to be better.

Re: Converting a Johnson 9.9 to a 15 hp

Fireman, actually i have three motors, a 6, 4 and a 9.9. ive already been on the water and am waiting for nothing.<br /><br />i may not have posted much here but i can assure you i have been on this site for 5 years now. ive had bad days also and still not taken it out on someone.

Re: Converting a Johnson 9.9 to a 15 hp

Well...I think Dan was just trying to help get Mo in the right direction....and fireman was just throwing in a little humor. I don't think either meant any disrespect towards Mo. But some folks tend to take things differently than I do.....<br /><br />And that 9.9/15 site is in the FAQ section of the forum. The gent that wrote that article was kind enough to let us use it in the FAQ. My problem is I keep forgetting it's there.....

Re: Converting a Johnson 9.9 to a 15 hp

Again Mo,my apologies. I'm glad that you seem to be in the minority as far as getting on the water. Also glad that you have been around for a while. Please stay. OBJ, you were right.

Re: Converting a Johnson 9.9 to a 15 hp

i had nothing but good intentions...you had posted that you couldn,t find the right words to use when searching ...i found you the right words.there is a ton of good info in the 43 posts you will find.i in no way insinuated that you no longer post any more questions.i often enjoy reading the posts that i find when searching for a topic i want more info on.i guess i thought you may get some useful info by reading them also.also,when a topic has been covered alot you may not get as many posts from the very knowledgable people that may have spent hours typing the same answers several months ago.