1996 115 johnson loses power at high speed

guyinfl27

Cadet
Joined
Feb 15, 2008
Messages
15
Hello everyone, I have been having some issues with my motor losing power at high speed. This has happened the last two times I went out. I will be cruising along and the motor will start to lose power at go back down to about 1500rpm and then back up and back down. Sometimes it will shut off completely. The primer bulb is solid when this happens and I don't think I have any air leaks in the fuel lines. It only does it when I am above 3/4 throttle and I have had to chug back to the ramp at slow speed. I just rebuilt the carbs, new fuel pump, new filters, new fuel tank, and new alcohol resistant fuel line. The boat ran fine right after the carb rebuild but it sat for a couple months and I have been having the problem ever since. I am at a loss and this has been really frustrating. Oh yeah, the motor is really hard starting sometimes and even when it sits for more than ten minutes it can be hard to start.

I am thinking that maybe the carbs may still have something stuck in them that i missed because it seems to be a fuel issue. Can anyone give me any ideas what else to check?
 

SparkieBoat

Captain
Joined
Aug 17, 2009
Messages
3,643
Re: 1996 115 johnson loses power at high speed

you need to do a visual on the carbs while running with it acting up, you can tell if one has a bad spray pattern. also I would get a spark gap tester from an auto parts store and check the spark on each cylinder. Remove all plugs and test spark on each cylinder it should produce a blue spark across a 7/16 gap. Put new plugs back on motor, make sure you get the right plugs for your motor.
 

Crashtackle

Cadet
Joined
Nov 25, 2009
Messages
29
Re: 1996 115 johnson loses power at high speed

Have you noted what temperature your motor is, when this is happening?
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: 1996 115 johnson loses power at high speed

Is the float and needle inside the vapor separator clean, moving freely and set correctly?
 

guyinfl27

Cadet
Joined
Feb 15, 2008
Messages
15
Re: 1996 115 johnson loses power at high speed

thanks for all the replies. i am going to try the spark gap tester first and go from there. i don't believe the temperature has anything to do with it because my temp gauge reads in the right range at all times and i have had the problem when its leaving the ramp still warming up.

What do i look for to tell if the carb has a bad spray pattern?
 

SparkieBoat

Captain
Joined
Aug 17, 2009
Messages
3,643
Re: 1996 115 johnson loses power at high speed

remove carb cover and look into carbs while running, you should see and even spray in each carb, if one has a noticeably smaller spray than the others, clean/rebuild carb.do not run your motor very much if you see a bad carb because you are creating a very lean condition for that cylinder and thats bad..do not run your motor for an extended period without cover in place.
 

jack450

Cadet
Joined
Apr 12, 2010
Messages
17
Re: 1996 115 johnson loses power at high speed

Hi had similar problem with my 96 merc 60. It turned out to be a bad hose from my oil tank . if you have oil injection system good luck
 

bob johnson

Rear Admiral
Joined
Feb 25, 2009
Messages
4,304
Re: 1996 115 johnson loses power at high speed

ok I found it...

24v71ub.png


but I wonder how much influence this can have on your fuel system...

seems like a lot!!!

this is the first i have heard of a vapor seperator in the system...


bob
 
Top