1990 Johnson 15hp dies at high throttle

[a2marian]

Hello everyone...just joined the forum today and am new to the boating community..Just purchased a used Johnson 15hp 2 stroke the other day...great compression between 130 and 135 psi in either cylinder..anyways I had my motor on a mount and in a garbage bin running the other day on my driveway to test it out...changed the spark plugs and gave her a rip, she started on the third pull or so but I think that's because there was no fuel to the engine yet...she idles very nicely to warm up and when in gear as well but when I put it in neutral and rev up the engine to full throttle, it begins to die and eventually cuts out...pulling the choke in and out when this happens help a bit but doesn't allow the engine to maintain the higher rpms...my guesses are that either there is something up with the old carb (perhaps gummed up from the years of use) or that the exhaust (which comes out in abundance when you rev the engine) which surrounds the stationary motor is not allowing the engine to breathe properly, meaning the engine is pulling in exhaust filled air as opposed to clean air...this wouldn't happen on the water i presume because you are moving and the air around the engine is constantly changing...any help would be great! I'm a newbie at all this but am willing to learn a lot in the name of fishing and boating. Thanks all!

[cajuncook1]

Please don't rev WOT(wide open throttle) with your motor on ear muffs or in trash bin. This can cause your motor rev very high (rpms above the manufactured recommended range and BAMM, throw a rod.)

The excessive smoke could be that the motor was fogged(producted designed to leave an oil residual/coating on the internal parts for protection and prevent rusting) prior to being put up.

Very possible that your carburetors high speed jet may be fouled are gummed up.

Another though is that you may have some trash or tarnished fuel residual occluded the filter screen in your fuel pump causing a lean or fuel supply issue at higher speeds.


Here is a link with a lot of good information regarding your motor.

http://www.sschapterpsa.com/rambling...OMC%20info.htm

Here is a digital parts breakdown of your motor. (choose your model from the list)

http://www.marineengine.com/parts/jo...ear=1990&hp=15

Good luck, lots of experts regarding your motor on this forum. Hell of a good motor and very dependable with simple yearly maintenance.

[AlTn]

do not rev to wot in neutral....in gear and in a barrel with water level a few inches below the exhaust relief ports try not to exceed a high idle ...exhaust gases do influence running state...new to you motors...check out the advice under Top Secret Files....wealth of info on this series of motors..google.. Leeroy's Ramblings..outboard motor related articles..9.9/15 hp....buy a factory OMC manual for this engine <ebay,outboardbooks.com, iboats>...specific to running out of fuel at high rpm..does pumping the primer bulb at high rpm. make a difference in the way it runs?
I'd put replacing the waterpump number 1 on the list and make certain the engine isn't overheating..should run 140-160 degs. when warm. The quickest way to really harm that engine is to overheat it.
Post back as many here have experience with that series of engines..in fact..just using the search feature on the forum will probably answer a lot of your questions

[a2marian]

Thank you all for the replies...when I ran it the primer bulb was hard...i'm going to purchase an omc manual and do a carb/fuel assembly cleaning...i want to be sure this baby runs like a 9.995/10 when i take her out on the water...water pump works beautifully, don't think there are any issues there...but would consider doing any preventative maintenance necessary while the weather is still cold out..what kinds of repairs other than the carb/fuel cleaning would fall under the preventative maintenance column for a motor in this used state?

[nwcove]

if you are unsure of when or if the impeller was replaced, you should change it. also inspect and change the gear oil. jmo

[a2marian]

Okay so ordered a service manual, carburetor repair kit, fuel pump repair kit, and water pump repair kit...i also ordered OMC triple guard grease, OMC gasket seal compound, and gear lube...also going to pick up a nice sized container of varsol from the local shop to soak the carb in...am i missing any critical tools that perhaps the average joe might not have?

[AlTn]

not for the work you've listed...google..Leeroy's Ramblings..outboard motor related articles..9.9/15 hp maintenance and repair...extensive info. w/pics on this series of engines...that fuel pump is a pita to rebuild in my opinion

[cajuncook1]

The carburetor kit and cleaning sound great as well as the changing your impeller. Wait on the fuel pump kit or changing the pump for the moment. You want make sure it is not a gummed or foul carburetor.

Check the screen on the fuel pumps intake to make sure it is not gummed are varnished up. It's easy. Just unscrew the large screw in the middle of the pump. The fuel coming the tank via the motor's fuel connector then the connector to the fuel hose to the fuel pump inlet. That screen will occluded with trash. Clean it or replace(screen) if is occluded. A partially occluded screen can cause a fuel delivery issue.

Do the simple and cheap stuff first and then move forward.

[a2marian]

Okay so an update...got everything in the mail recently and completed a gear case oil change, water pump rebuild, fuel pump rebuild (which took a lot of patience), and am currently working on the carb (where I'm stuck waiting for a new float bowl)...I cracked the darn thing when I was screwing it onto the bottom of the carb..I'm just waiting for the local marine to get the part in...since the stuff was taken out, I took the time to clean all the crap and gunk around the inside....am i missing anything? Oh and I'm looking into purchasing a 1976 Johnson 2hp as a trolling motor for $300, any input?

[nwcove]

unless the 2hp is in mint condition, the price is a bit high for a 35 year old motor. ( which will probably need a carb kit, water pump, and gear oil change at the minimum)

[a2marian]

I was hoping to negotiate with him on the price...ad says it had the water pump and tune up recently...but i understand that I should do the work on it regardless..not that i mind it...i think im addicted to these motors.

[nwcove]

ahhh......ya got the outboard bug!!! look around for a mid -fifties 5.5 johnson.....once you find one that is servicable ( not a hard task) your bug will be uncurable! lol