Johnson 25hp will only run on land

[00V8]

Just as the title says, my 25 hp will only run out of the water. When you put it in the water barrel or on the river it tries to run but horrible. Has good spark, compression is 90 on top 87 on bottom, and the carb was just rebuilt because i thought that was the problem.


Any ideas?

 

[nwcove]

Re: Johnson 25hp will only run on land

link and sync may help, but whats the history on the motor....worked great? worked great then went bad? etc ( a model number would also help!)

 

[phillnjack2]

Re: Johnson 25hp will only run on land

well you shouldn know if it worked without any water ? unless your using water muffs and hosepipe etc.
if your starting it up on land with no water at all then , youve probably killed it.


the compression is also very low, exactly how are you doing a compression test ?

explain your routine with this test.


phill

 

[00V8]

Re: Johnson 25hp will only run on land

Yes i started it with out water, no the motor is not cooked. I'm not a moron and don't let it sit and its not going to damage it just running it for a minute.

As far as history, i think it is a 1976, it has been in my family for about 20 years. It has never been very reliable and has left us stranded for no apparent reason many times, normally seeming to repair itself.

Some days in ran great, some days it didn't want to run at all. I have changed coils, impeller, carb, plugs, ect. Now, as i said, it doesn't real run at all.

Compression was checked one plug in, one plug out, no oil in the cylinders our anything using a cheapo harbor freight gauge. When checked before it always showed 115 and 120 but my good gauge was stolen. It had not been ran since it was last checked. I just picked the lowest of the recorded numbers because i know it has at least that.

Sorry for any typos, on my phone.

 

[nwcove]

Re: Johnson 25hp will only run on land

just a tip.....if you ran it for a min or two without water, you probably cooked the impeller.....they are water lubed ya know!! with that being said, from my experience, most hydrophobic motors either have an electrical issue that shows up in high humidity. ie...near the water, or need to be sync'd. ( assuming that the motor does have acceptable compression) jmo

 

[ronward]

Re: Johnson 25hp will only run on land

You may not cook the motor that quickly, but the impeller will go very quick with no water. Sorry nwcove, I was typing when you posted first

 

[Cap'n Chaos]

Re: Johnson 25hp will only run on land

How did you establish that it has good spark?

 

[boobie]

Re: Johnson 25hp will only run on land

If you let it run for a minute dry you probably cooked your impeller.

 

[00V8]

Re: Johnson 25hp will only run on land

Well, once again it has seemed to fix itself. Let it run for about an hour at varying rpms and it never died, restarted it on the first pull 5 more times. The throttle seems out of adjustment though, it has a stick in it when it goes to idle and it makes it difficult not to kill it. Impeller is still good, pumping good water and the head never gets hot. I planned to change it this year anyway though.

 

[00V8]

Re: Johnson 25hp will only run on land

Replaced the impeller and had it out for around 4 hours this afternoon with little issue. I need to perform a sync and link though.

When the throttle is all the way down in the off position it its way past the alignment marks on the flywheel.

How do I adjust this?

Thanks for the help all!

 

[phillnjack2]

Re: Johnson 25hp will only run on land

NEVER NEVER NEVER
run the motor for even a second without water at the impeller.
even just cranking it over can and often does destroy an impeller in just a few seconds.

Maybe you have been ultra lucky, but never post again saying
"Yes i started it with out water,
I'm not a moron and don't let it sit and its not going to damage it just running it for a minute "
that is asking for trouble and possible responses that you might not like.

nobody said your a moron, you just have never been told about what happens to impellers.

for example my engine will shoot water from the tell tale when cranking it over within 10 seconds !!
that just shows the impeller is spinning in the pump good and working correctly.

lots of folk end up saying
"well i looked at the impeller and its fine so put it back, ...running dry didnt hurt it"
now look again and youl see its probably spun on the hub and is useless, but looks great.
ive posted a example pic below of this very thing from 140hp engine.

Now take out both plugs once the engine is warmed up and then check compression of each cylinder with the
throttle on fully open.
only needs 10 seconds on each (but make sure water is getting to impeller).
this will give you proper readings, even the cheapo compression testers are not far out at 100psi.
ive had testers costing over ?150 and testers costing ?10..just 2 psi difference !!!! so nothing to worry about.

also
if you always use the same comp tester you know where your are with future readings.

no engines fix themself,
we just think that while they run for a while seemingly ok, but when we are relying on them to get us
out of trouble, this is when the "fixed"engine proves it was only joking !!!!!

once you get it synced it might just be a real good engine that will run for many more years.
if its been sitting a long time the rings could be sticking a bit and maybe a tin of decarb is needed, i always
do this anyway as im convinced it keeps the engines real clean of carbon build up and lets the power flow.


1 X SPUN HUB IMPELLER, but the rubber looks great !!!!!
This WAS due to running without water for 1 minute !!!!!!!

 

[00V8]

Re: Johnson 25hp will only run on land

We are still on the impeller problem i see. As i stated, i planed to replace it, which i did. The motor had been sitting for 6 years since it was used regularly so i knew the impeller was trashed, that's why i didn't really care about it. I wanted to see it run.

Now I'm needing information on the sync and link process.

Have any knowledge on that subject?