So my older 15hp Johnson is bogging down at full throttle. Had it in twice last year to address the issue and it appears it still isn’t resolved. The gas, I have is probably at 2 years old since last year it was pretty much in the shop the whole summer and I have not put new in the tank. Wonder if it could be the gas affecting the performance or maybe the motor is starting to reach its life span as its probably close to 30 years old. Thanks.
If it’s not smoking I don’t think the life is up that.
Drain the gas. Put in fresh. Replace the filter. Be sure the primer ball is good. Add a good cleaner to the gas. If that doesn’t fix it call Sheldon. 
If it’s not smoking I don’t think the life is up that.
Drain the gas. Put in fresh. Replace the filter. Be sure the primer ball is good. Add a good cleaner to the gas. If that doesn’t fix it call Sheldon.
Skip everything and call Sheldon. He pulls rabbits out of his…. then ask him m about my charger 
Get fresh gas.
Wonder if it could be the gas affecting the performance or maybe the motor is starting to reach its life span as its probably close to 30 years old.
No, the motor is NOT near the end of its life span. The 1980s and 1990s OMCs were some of the best, elegantly simple, and most bullet-proof outboards ever designed. If run with good oil and good fuel, they will run virtually forever. Replacement parts will be available for decades to fix what breaks.
Obviously, get fresh gas and get rid of that old crap. Eliminate the most obvious source of any problem first.
If you had that simple outboard in twice to ANYPLACE to fix the same problem, get a new mechanic. Seriously. I’ve worked on those OMCs since I was a teenager and I’ve fixed dozens of 9.9 and 15 OMCs. If your mechanic can’t figure out the problem, it’s time for a new mechanic.
First off, put in fresh gas and mix with Penzoil XLF or other high-quality oil. Then give it the Italian Tuneup. take it out and run it on the water as hard as you can. See if the problem goes away.
If that doesn’t work, almost certainly you’ve got a gummed up carb and/or you need a carb rebuild. Seldom will I bother removing one of these carbs without ordering a rebuild kit first as once you have gone through all the work of removing the carb, it’s so easy just to rebuild it and be done rather than just hope a cleaning alone solves the problem.
OMC carbs must be absolutely clean to run properly. A couple of times I’ve gotten in too big of a hurry and didn’t clean the carb thoroughly enough, so I had to do it a second time. I now let the carb marinade in the parts tank overnight, then clean it and rebuild it the next day.
Rebuilding these carbs is pretty easy but care has to be taken because the recoil starter has to be removed to get the carb out and that has to be done correctly so it doesn’t lose its spring tension. Also carefully observe the linkage and take pictures if you do it yourself so you can use them during reassembly. Do lot drop the nut on the left side of the carb so it falls down into the shaft housing.
Grouse
well,I was going to say something about rebuilding the carb first,but,if you give it the italian tune up first it wont matter as you will be shopping for a new motor.
gas,,,cheesenrice I could write a book on the effects of THREE MONTH OLD poop but I dont feel like wasting my time anymore.
Skip everything and call Sheldon. He pulls rabbits out of his…. then ask him m about my charger
I’m going to go get my popcorn and pull up the recliner for this? 
I’m just awaiting for the Paul Harvey “Rest of the Story” here,,,, 
Had it in twice in one year and you thinks it’s that gas???
What kind of shops are you bringing it too???
Had it in twice in one year and you thinks it’s that gas???
What kind of shops are you bringing it too???
gas is and always will be my first suspicion,compression test next yadda yadda yadda.
unless you do this every damn day of the week most have NO clue as to what sh!tty gas does to a motor,ESPECIALLY TWO STROKES.
if you are willing to admit that the gas is two years old,I will tell you you are asking the motor to burn tar.
carb clean/ignition quality first after all preliminary checks are made.
forty plus years experience says so !! and I dont give two sh!ts what anyone says.
Denny,Randy and I spent an hour on the phone going through his set up no less than five times to ensure things were proper.
we were also battling a very poorly written wiring diagram,I was almost at the limits of my abilities concerning ohms law especially when tying a DC unit in conjunction with an AC unit that serves a singular purpose on both fronts.
mapping out electrical problems in my noggin,,,well,lets just say it takes a bit in my old brain these days.
Randy,when we going fishing in my boat???
Been a concern for many years as my 250hp 2 stroke is damn near 20yrs old, still runs flawless. Yes, has the E in its name. It’s used heavy in the spring (tonka) & heavy in the fall (ely)…
I’d like to remove the 25 gallons of old gas in the tanks & start with fresh. Are there places that will empty the old gas?
Been a concern for many years as my 250hp 2 stroke is damn near 20yrs old, still runs flawless. Yes, has the E in its name. It’s used heavy in the spring (tonka) & heavy in the fall (ely)…
I’d like to remove the 25 gallons of old gas in the tanks & start with fresh. Are there places that will empty the old gas?
Can always blend it off in a daily driver.
I only run 91 octane in ALL small motors, lawn mowers, chainsaws, outboards, string trimmers, tillers, power washers, ALL small motors.
Splash a little sea foam or I use Polaris stabilizer in it.
Stay away from Staybil. Imo !
Replace any old gas in the spring.
Start with NEW 91 EVERY spring.
The old gas ?
My father in law and brother in laws and myself, have some old gas tractors.
Farmal M’s and JD 2 bangers, the old gas goes here.
Those older tractors will burn it, they have some pretty big jets and the old gas doesn’t seem to bother them, even with the 2 cycle oil in it.
Good luck.
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