25 Johnson Coughing/Miss in Mid-Range

[mtkinzel]

1991 25HP
Broken pull cord. Replaced. Broke again, included spring. Replaced spring and cord. Next time out boat cut back to 75% power at WOT.

Compression 110 and 105
Replaced both ignition coils
Spark jumps 7/16 on both.
Installed carb kit and cleaned (both jets).
Replaced reeds.

Linc/sync is done (cam roller marks/butterfly positions)
Sea Foam decarb done
Replaced plugs QL77JC4

Test run results: Idled great. At WOT still at 75.....removed cowling and it ran FULL 100% WOT. Cut motor off. Started fine and ran well. Put cowling on and it did not run 100% WOT. Showed cough, sneeze, miss just above idle in mid range and would not get to top speed. Fuel line bulb gets soft and hard with the cough and sneeze (like it corrects itself). Stays hard at idle.

I am inclined to think it is in the high speed jet or fuel pump. I do not have experience to draw on to fix this. Seems it is fuel related or timing related as symptoms developed very soon after broken pull cord but what do I know. If it is fuel related what do you all think my next step is? Just take it to the dealer and pray? Cost may be more than it's worth at this point.

Thanks for this site.
Mark

 

[Cofe]

Re: 25 Johnson Coughing/Miss in Mid-Range

Some things to check would be, replace old fuel lines, check and clean the gas tank vent, check the fuel pick up line in the fuel tank "some of them have a screen that will plug." Make sure all fuel line connections are good and tight with good clamps.

You could also be right thinking that the fuel pump could be failing.

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

I have a new tank and hose. When I put in the carb kit I also changed out the fuel lines from the primer to the carb and intake (5/32 ID hose and the .0575 ID hose).

 

[Cofe]

Re: 25 Johnson Coughing/Miss in Mid-Range

Another thing to check would be the screen in the fuel pump. Remove the big flat blade screw to get to it.

 

[johnny 30]

Re: 25 Johnson Coughing/Miss in Mid-Range

Hello:
You said when you took the cowling off it ran 100%,with the cowling back on it only ran at 75%.You may have an exhaust leak,filling up the cowling with exhaust fumes.Carb is not getting clean air (fuel/air mixture),something to consider.Good luck

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

Regarding: Hello:
You said when you took the cowling off it ran 100%,with the cowling back on it only ran at 75%.You may have an exhaust leak,filling up the cowling with exhaust fumes.Carb is not getting clean air (fuel/air mixture),something to consider.Good luck
I tested it again without the cowling and could not get it to 100%....got frustrated and returned home.

I just pulled the fuel pump cover and cleaned the screen (it did not appear dirty). I removed the tank pick up tube and checked to ensure there was no blockage. I checked and reset the vent cap so that it was vented.
I ran it on ear muffs and it still idles well (low rpms) but the moment you give it a bit of throttle it coughs, sneezes, misses BUT does not cut off. I pulled one plug wire at a time to see if I had a bad cylinder and the motor continues running as I remove each one independently (had to check again.)

If I put my hand over part of the carb, say 50% or so it does improve the symptoms somewhat (could it just be a carb issue still?) It has a primer on it (pull it out and it goes back in on its own). I have tried pulling it out while the motor is missing / acting up and it does not seem to affect anything. If I push it in all the way (to what appears farther in than its normal resting spot) the symptoms get worse. Could my primer be an issue here? Or could the fuel pump diaphragm be leaking ? There are no visible leaks around the pump or primer. Could it be leaking into the exhaust hole? How do I see if my diaphragm is bad? Would the fuel line bulb remain hard if the diaphragm is bad? Oh my.

 

[fmalott]

Re: 25 Johnson Coughing/Miss in Mid-Range

sounds like my problem i had recently with my 1980 johnson 25hp idled at low speed good high speed coughs sneezes,misses the problem was the high speed jet was cloged, I unclogged along with rebuilt fuel pump problem solved runs at low speed and high speed with no coughing sneezing or misses so i suggest carb rebuild make sure you clean out high speed jet with a wire or something similar carb cleaner will not unclog sometimes

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

Cleaned carbs! Removed orifices, soaked, ran wire thru, blew air thru AGAIN. Readjusted float. The carb is not that complicated and I am confident I have it clean and jets/orifices clear.

I will run it with a gallon of new gas/mix with Stabil when this rain stops. Old gas was not old (within last twenty days or so and treated with stabil). If no improvement I will replace the fuel line from tank to motor connectors (although the complete line and connectors are new this season and have no more than an hour use of run time and six months in possession). If this shows no sign of improvement I will open up the fuel pump to inspect the diaphragm. After that, it goes to the tech.

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

Looked at the leaf petals last night when I had the carb off (another soak and clean). I did replace them a few days ago and they still look ok.
For the fp.....I disconnected the line leading to the carb and squeezed the main fuel line bulb and gas came through. I reconnected that line and removed the fp from the housing (two screws). I again squeezed the the main fuel line bulb and the fp did not leak ( I was looking for fuel around the fp and out the rear hole but it did not leak) and the lines appeared to prime correctly.

I checked the cam and butterfly sync with the throttle by eye and all appeard well.

Morning test: One gallon of fresh fuel mix with Stabil. Motor fired, idled well, NO miss, hesitation, hiccup, burp, stumble. Well then I am thinking to myself. Ok, so what is causing these problems? I cut it off, let it sit. Repeat test three times. I can not get symptoms to appear. Cut off let it sit. One more try. With motor running correctly I use the PRIMER! and WA-LA! SYMPTOMS return. (I know, why would I do that? I have three kids that are always in this boat with me and they love tinkering. It is something they have done in pretending to be the captain.) SO............After pulling the primer out, symptoms re-appear and motor can not clear itself back to normal after 5 minutes. I cut it off and pull then push primer in and out - does not seem to have regular constant pressure (different feeling on different pulls/pushes). After doing this a bit I restart motor and symptoms have disappeared. So, in trying to UNDERSTAND if this IT, I primed it again while motor was purring well and again it failed to clear itself until I continue to push/pull primer into a position that feels like it has pressure. Then ran smooth again.

Could this be it? Would a new primer (80 bucks) be in order or just the four o-rings(20 or so bucks)? I disassembled it and it seems rather simple. Rubber rings "look" ok but I know that is misleading. One seems flat as opposed to round. I am thinking there is hope still!

 

[outlaw241]

Re: 25 Johnson Coughing/Miss in Mid-Range

the primer is only used for cold starts, it should shut completely off when you push it all the way in. i just went through similar problems with my 25,i cleaned the carbs 3 times an on the 4rth time the little tiny tube thats inside a small tube on the bottom of the carb was plugged up. you have to find a really small wire to get in there ,well that cured my idol problem after i adjusted the air mix screw to 1 1/2 turns out. on the wot issue mine would run at wot a little ways then acted like it would drop a cylinder an it had plenty of water out the tale-tale but it was a little weak out the tale-tale at idol so i installed a new impeller an it runs like a top know, on the primer i also changed all the small hose with fuel line from a lawnmower shop the hoses you can see through just so i knew if it was malfunctioning.also my evinrude dealer said there was nothing wrong with my impeller but i changed it any way and i am glad i did. hope this helps

 

[northwoodslivin]

Re: 25 Johnson Coughing/Miss in Mid-Range

Had the same motor pretty much and I had those same issues as you. Are you 100% SURE you cleaned that carb properly? when I say properly I mean, did you pop out the two orifice plugs and clean in there? this is very important and what cleaned up my problems along with new fuel lines.

You need to replace ALL your fuel lines including the big one. They may look fine on the outside but trust me they have been getting eaten by ethanol if they are older then 15 years "they never started to make ethanol approved lines up until 15 years ago"

Also, are you sure you are not running lean? your low idle speed screw should be turned in snug then backed out 1.5 turns although it calls for 1 1/4 turns in the book I find that made my motor have a lean sneeze and run a tad warmer then usual.

I highly doubt your primer is to blame. Never use your primer after the motor is warm. Do this for your starting next time.

If your motor is cold, pump your ball up hard, then pump your primer 3 times and let it go to the red line "almost all the way in" start the motor and let it run for 25 seconds like this then push the primer all the way in. After your motor is warm you never need to use your primer, and mostly on hot summer days it is not really required, maybe one pump and return it to closed position.

The issues I had was my fuel lines in the end, I ended up cleaning that darn carb 4 times until I figured out it was my lines "thought they we're good because they looked like new on the outside" So it is very important to replace every single fuel line on that motor, and pop out the plugs in the carb and clean in there "found pieces of fuel line in mine under those plugs" and blow it out with 120PSI in every passage.

Good luck.

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

Carbs have been broken completely down, soaked, orifices checked and gone thru with wire and blown with compressed air (compressor). Orifices too-same way.

I have not YET replaced the fuel lines connecting to the fuel pump but did the others linking the primer and carb.

I am aware of the primer use and function. However, when the primer is pushed all the way in after warm up the motor stalls. The motor will run if it is ever so slightly out, but not out like 1/4 of the way.

The idle adjustment seems fine and set at 1 and 1/2. The motor runs WONDERFUL except for this intermittant problem. It would seem to me it is either the fp, hoses connected to the fp or the primer not being sealed internally. I have taken the primer apart for cleaning and will test it again. Then it will be the fp hose replacement as that is highly rec. anyway. Then I am left looking in to fp, again. Will have it figured out before 3 Friday as it has a service repair appt. at that time if not figured out.

 

[northwoodslivin]

Re: 25 Johnson Coughing/Miss in Mid-Range

hmm.. what happens if you press the bulb when it is coughing? For sure, replace all your lines. This could be your problem as tiny pieces of fuel line rubber are coming off of those old lines. I would get a fuel pump rebuild kit, their only around 20 dollars. Sounds like it might be your fuel pump, but it almost sounds carb related as well.

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

When it acts up priming the ball has no effect whatsoever. In fact, the ball does not seem to lose its prime completely instead becoming soft-er but not empty. I am replacing the remaining two lines from the fp and doing a fp kit.

Will provide the final result soon .... may just be bad fuel lines, clogged carbs, fuel pump issue, primer debris, and more. What is funny, not, is that is was running top notch and BAM. Hopefully with these minor, and I do believe they are minor considering what some face, the motor will continue to serve us well.

 

[northwoodslivin]

Re: 25 Johnson Coughing/Miss in Mid-Range

They are great motors and if taken care of, will out live you For sure replace the remaining lines. Probably going to have to clean the carb again. Before hooking up the carb after putting on the new lines. Hook your fuel tank up to the motor "with the carb not installed yet" and flush out your system "pump the primer and squeeze the ball and make sure you get any debris out that may be in there from the old lines. Rebuild that fuel pump and I bet you will be good to go!

Let us know how you make out!

 

[mtkinzel]

Re: 25 Johnson Coughing/Miss in Mid-Range

Thanks again to all for helping me with this issue. I will know tomorrow morning about 7am the final results of my "experimenting" the minor issues with this motor.

Original Issues: Broken pull cord, loss of power, mid range miss/cough (nearly all at once).

I was lucky enough to benefit from these boards and others in doing many things for the first time. Compression and spark check for one (or is that two?)

New ignition coils, fuel pump kit, carb kit (and cleaned three times), primer soak and clean and replaced o rings, decarb, all fuel lines replaced, linc and sync, just to name a few.

After doing the fuel pump and finishing the primer assembly about 2pm today I ran it on muffs and completed the same test as before and I am happy to report it ran beautifully with no miss or issues at all. Like a new motor. Tomorrow morning I will do a test run on the water but am confident this problem is solved. I had nearly lost hope but kept at it. Thanks to all who chimed in.

 

[northwoodslivin]

Re: 25 Johnson Coughing/Miss in Mid-Range

Glad to hear a happy ending, and your welcome