IS THERE A HIGH SPEED JET ADJUSTMENT ON MY 1998 25HP

[bobgritz]

The Patient: 1998 Johnson 25HP Model J25RECB

The Symptoms: The motor 'misses' or 'coughs' at both slow and high speeds (under load or not). In other words, as your motoring at say 3/4 speed, you can feel the motor essentially cutting out momentarily. It's almost unnoticeable to a casual boater but it's irritating as &%$# to anyone with any decent mechanical sensibility. Please excuse the following, and as weak as this next illustration/explanation is, it's kinda like ... miss ... miss miss ... miss ... miss ... miss miss ... etc. You probably know what I'm talkin' 'bout!

The location of the fuel adjustment screw is obvious and I've made the traditional 1 1/2 turn adjustment (+/-). I was wondering if there is an adjustment for the high speed jet (a non-outboard mechanic told me to tweak this)? However, according to the usual online sources, and after looking at the carb diagram, I suspect it is a fixed setting with only an 'orifice plug' guarding it which I assume is for access & cleaning purposes only.

Perhaps it's electrical but I'd prefer to start with carburetion and go from there.

Any thoughts. Thank you.

 

[hardwater fisherman]

I dont think there is a high speed adjustment. But the carb could be blocked in the high speed jet. Or the fuel pump could be failing. Also check for good spark.

 

[F_R]

No high speed adjustment. The orifice plug meters the fuel better than us mortals can. Are you sure it is a "miss"? Does it feel like you are hitting something? Could be the clutch dog jumping in and out of gear.

 

[ondarvr]

Is this a new issue, or has it done this for a long time?

​Clean the carb and check for spark, plus check the compression, all are easy and quick. You'll know the issue after that.

 

[racerone]

Run with a timing light and observe the flashing light.--------Install new plug wires and boots perhaps.

 

[bobgritz]

I should have mentioned at the beginning that the compression is 120 in both cylinders so I feel comfortable ruling out this area. I don't have experience with this motor since I just got it from a friend and it had sit for a number of years. With that in mind, I pulled the carb and the bowl was spotless. I soaked it for 24 hours then blew out all the accessible openings. I will plead guilty to not removing the plugs so I cannot give myself an A. Maybe a B+. Perhaps I need to revisit the fuel mixture setting ... could this be causing the subtle hesitations I'm feeling? I'm leaning away from the clutch dog only since it appears to be having its spasms even when running with the ears and not in gear. Timing is definitely a possibility and can anyone point to a good source describing how the actual adjustment is made.

 

[racerone]

Timing on these motors does not go out of adjustment.---You use the timing light to observe spark behaviour !----And go ahead open the lowspeed mixture to see if there is improvement.----And are you sure the stop on the rod that goes to the towershaft is adjusted correctly ?