88 Johnson 25 won’t rev

[Ampegor]

Hi all,
I have a 88 Johnson 25
It will start and idle perfectly for hours
Will run at slow speeds but as soon as you try to go past about 1/3 throttle it dies out and wants to stall if you don’t reduce throttle.
The engine has good compression 120 top and bottom
Not fuel related as I switched out a known good carb and fuel pump and exactly the same outcome.
New water pump and thermo stat engine runs a nice even temp.

i am suspecting coils or CDI box.
I am looking for ideas. I am not sure about CDI I always though they worked or didnt
And if coils why does it idle so well hot or cold

thanks in advance for any ideas
Andy

 

[racerone]

Fact.---They will run very well on one cylinder.----So check and see if you have spark on both leads.----I say it is running on just 0ne.

 

[oldboat1]

good carb and fuel pump, but maybe bad fuel (think water). Try a portable tank with a gallon of fresh mix.

 

[James R]

My favorite. I love these 25Hp motors. It certainly sounds like a fuel issue. Try this. Fill a spray bottle with fuel mix. Get on the pond and get her going. When she starts to falter spray fuel mix into the carb throat. If she picks up its a fuel problem. Now chase it.

 

[Antlergang]

Currently having a similar sounding issue with my 1971 Johnson 40hp electric start. We can go for a long joyride at 5ish mph, but can’t get anything else out of it. Replaced sparks, new fuel tank with new gas (0 ethanol too). Shifts normally, starts every time. Doesn’t seem to be related to throttle linkage. Keep me posted if you make progress here.

 

[racerone]

Antlergang----It sounds like your motor is running on just 1 cylinder.----Post compression test numbers.----And does spark jump a gap of 1/4" or more on a simple test device ?

 

[Antlergang]

Antlergang----It sounds like your motor is running on just 1 cylinder.----Post compression test numbers.----And does spark jump a gap of 1/4" or more on a simple test device ?

I’ll do some digging and come back with more information. Thanks!

 

[oldboat1]

Antlergang, come back with a thread of your own, including the info about your motor included in this thread.

 

[ct1762@gmail.com]

Currently having a similar sounding issue with my 1971 Johnson 40hp electric start. We can go for a long joyride at 5ish mph, but can’t get anything else out of it. Replaced sparks, new fuel tank with new gas (0 ethanol too). Shifts normally, starts every time. Doesn’t seem to be related to throttle linkage. Keep me posted if you make progress here.

is the carb butterfly opening horizontal at full throttle? armatur plate advancing all the way? the high speed needle... behind it everything clean?

 

[racerone]

I do not believe there is a high speed needle on a 1988 model 25 HP carburetor.

 

[ct1762@gmail.com]

i thought he was talking about a 71' 40hp. Which i believe did have an adjustable high speed needle, like the older big twins or could be mistaken?

 

[racerone]

Sorry ---I looked at post #1 about a 1988 model 25 HP.

 

[Antlergang]

So for the 71’ Johnson 40, it turned out to be completely carb related. After finding that I had spark in both plugs, good compression, and new gas tank/fuel lines/filter, I focused all attention on carb. Sure enough, my high speed pin wasn’t closing due to a blockage, and gas wasn’t making it in. I took it out and cleaned it, and then ran with some sea foam and the engine runs like it’s summer of 71!!!
hope this helps with the 88 in some way, good luck lad