Johnson 115 runs great for first 10 min, then runs like crap

[Maxum21]

good mornin,
Had my 18' Larson w/1996 Johnson 115 out for the second time yesterday since purchasing it and i'm having issues. Both times out the motor ran great at all rpms for approx 10-15 minutes then started to to choke/bog down and die (for lack of better words). It would start back up and ilded fine all day, but at higher rpms it would run very poorly. Wot would basically kill the motor right away. I really want to say it seemed like a fuel issue, but why would it take 10 minutes to act up? i tried pumping the primer bulb while running it but that made no difference. After my first time out, I looked over the fuel lines, checked filters, changed plugs, mounted a new water/fuel seperator but still had the same symptoms yesterday. Confused and frustrated. Any advice?
thanks
Jamie

 

[Maxum21]

Re: Johnson 115 runs great for first 10 min, then runs like crap

forgot to mention, its a premix motor(was injected at one time) but now has just the standard basic fuel pump. And also, after purchasing boat, i drained all the fuel i could, and added premix with synthetic xd-50 oil. Now the marina says that oil is fine for premix use, but the plastic container only mentions oil-injection. Could the oil be possibly causing problems? i dont see why it would but i dont know for sure

 

[freelance marine]

Re: Johnson 115 runs great for first 10 min, then runs like crap

Good day

I am in the boating game and have been doing motors, i have trouble similar to yours a number of times especially on the 115 and 130's i have found it to have been the water pump impellers that where the problem even thought the motor was pumping and not show any signs of over heating, i found that the impeller was slipping on the bush that has keyed on the drive shaft and with it slipping you are not getting water to the furthest piston from the pump.

Your heat sender would pick that up and restrict the revers on the motor which would make it run very uneven and rough.

Hope that helps

 

[Maxum21]

Re: Johnson 115 runs great for first 10 min, then runs like crap

interesting. so your saying one cylinder can be overheating? wouldnt the overheat alarm still sound if that were the case?

 

[bob johnson]

Re: Johnson 115 runs great for first 10 min, then runs like crap

an overheated motor that has gone into SLOW mode wont run poorly at WOT...it wont get to WOT!! the rpms are limited to about 2500 by design!! the motor should sound fine up to 2500 rpm then miss excessively....because the electronics are cutting out spark by design..

plus the alarm should sould...constant...

the only way to get out of SLOW mode is for the temps to drop below 180 ish AND the ignition is turned off!! BOTH have to happen..


you probably have a fuel restriction somewhere.....be carefull you could lean out the motor and burn up a piston or scour the cylinder walls running lean.

try running from seperate above the floor portable tank.......skip all the connections you ahve now and go direct to the motor....

it is possible your fuel pump is weak......

we need more info.....

get a infared thermometer and verify temps.....try pulling a plug wire while running and see if nothing changes on one of them...

at least youll know the offending cylinder....if thats the issue

check compression

check spark

get back to us

bob

 

[Maxum21]

Re: Johnson 115 runs great for first 10 min, then runs like crap

I NEVER UNDERSTOOD WHY MOST OUTBOARDS DONT HAVE TEMP GAUGES!?!? this situation among many others is why they SHOULD all have one. Makes no sense whatsoever. Yea an overheat alarm is nice but it doesnt replace a temp gauge.
Anyways Bob i'm going to start running the tests you mentioned. I bought a psi suction gauge a few weeks ago. Do you know what psi these pumps should be at? ....freelance marine may be on to something. yea the alarm should be sounding if overheating but maybe its not working. the fact that its runs fine for 10 min could certainly be an overheat issue. If the motor was put into "slow mode", would it still be able to rev past 2500 in nuetral? thanks for helpful info! much appreciated. will post back after i run these tests

 

[Maxum21]

Re: Johnson 115 runs great for first 10 min, then runs like crap

just for the heck of it i ran it in a barrel for 15 min. pulled the cowling. the 2 right(starboard) cylinders were significantly warmer than the left 2cylinders. I dont have a temp gun yet, but to the touch there was quite a diff. is this normal?

 

[Maxum21]

Re: Johnson 115 runs great for first 10 min, then runs like crap

ran it another 20 min in barrel, left cylinder heads were 102 degrees and right side was 122deg. motor is pumping good water.

 

[Silvertip]

Re: Johnson 115 runs great for first 10 min, then runs like crap

1) Runs like crap is not a very good description. Does it feel like it drops a cylinder or what?
2) When you turn the key to RUN (not start) does the alarm system provide the beep that tells you the system is working. You can check the over temp and alarm system by disconnecting the wire going to the temp sensor. Ground that wire to the block and you should get an alarm.
3) Temp gauges are not used because just like in a car, most people have no idea what it means until the engine quits. That's why idiot lights were put in cars since a red light usually meant something bad. Turns out that didn't work either as people still though it was ok to drive another 100 miles before having it looked at.
4) You likely have a a) a fuel restriction, b) a fuel tank vent line plugged, c) a weak fuel pump, d) an ignition system that is breaking down under higher temps.

 

[bob johnson]

Re: Johnson 115 runs great for first 10 min, then runs like crap

ran it another 20 min in barrel, left cylinder heads were 102 degrees and right side was 122deg. motor is pumping good water.

well...thats not hot at all....as a matter of fact that is pretty cool ...even for idle.

HOW are you checking that temperature?

second, your motor may run fine at low rpm and then over heat at higher rpms, and one reason could be a weak water pump, not pushing enough water to cool a motor fireing and creating as much friction as it does turning 4000 or more rpm.

your original complaint could easily sound just like a floating fuel restriction in your gas tank.....floats around until it gets sucks up to the intake spigot and blocks it off......shut the motor down, trailer the boat around...the debris could float back around the tank again.

not saying for sure....but that is a big possibility. also since i have come here I have heard of many guys who have similar problems and it ends up being a bad electrical componet that went out of kilter at a certain temperature...

and lastly...it could be a dirty-clogged carb or carbs

most likley a fuel blockage or electrical part bad


good luck

bob