Johnson 25hp problems

[Orkney seacrawler]

Hello Everyone I am in need help, I have a Johnson’s 25hp 2stroke. it’s starts up for a split second and then cuts out, It has good equal compression on Both cylinder. A good spark, I have changed the following

Fuel tank
Fuel line and one way valve
New fuel pump
Carb rebuild kit
Spark plugs

I just don’t know where to go next. Any help would be greatly appreciated. Thank you

 

[racerone]

A 1969 model or a 2005 model ?----Does spark jump a gap of 5/16" or more on a testing device ?

 

[Orkney seacrawler]

I’ll

A 1969 model or a 2005 model ?----Does spark jump a gap of 5/16" or more on a testing device ?

im sure it’s the later model I have attached some pictures below. I will check the spark gap again. And get back to you

 

[flyingscott]

What is your starting procedure?

 

[oldboat1]

could be remaining carb issues. Try spraying 50:1 mix into the carb throat to keep it running. Pull off the fuel pump hose at the carb while cranking and see if fuel is flowing.

 

[werewolf30]

I would look at the wiring on top around the timing plate for broken wires first, then take fuel hose off carb and pump the primer pump and see if gas comes out carb hose , look at the cdi module wires and the grounds , do a voltage drop test with a fluke dm or equilivant and see if you have voltage to it , leroys ramblings has some online wiring diagrams and i think there are some on here also , it looks like you have about a 2001 or 2002 but you can look up your model number online to see, it does make a difference on yr models. im thinking you may have a cdi module issue . but check it out first.

 

[Orkney seacrawler]

Hello Everyone I am in need help, I have a Johnson’s 25hp 2stroke. it’s starts up for a split second and then cuts out, It has good equal compression on Both cylinder. A good spark, I have changed the following

Fuel tank
Fuel line and one way valve
New fuel pump
Carb rebuild kit
Spark plugs

I just don’t know where to go next. Any help would be greatly appreciated. Thank you

Hi guys sorry it’s taken me a while to reply. Had some major surgery to my hands what has put me behind a tad.
I am still having a problem with the engine adding to the list above I have replace the following
Cdi units
Fuel solenoid rebuild
Plug caps and leads

I have noticed it seems to be flooding quite a lot.
Also when I connect a direct fuel line to the Fuel pump on the engine it starts but has a lean sneeze. BUT If I connected the fuel line correctly to the engine it won’t fire hope this makes sense I will try posting a video asap

 

[Orkney seacrawler]

could be remaining carb issues. Try spraying 50:1 mix into the carb throat to keep it running. Pull off the fuel pump hose at the carb while cranking and see if fuel is flowing.

Hello mate I have removed the hose while cranking it has a good fuel supply it’s also had a fuel carb rebuild all jets cleaned out.

 

[racerone]

Facts first.----Compression test values must be posted.----And does spark jump a gap of 3/8" ( 1cm ) on both leads ?----Water pump impeller replaced ?----Is throttle plate properly adjusted ?----If throttle plate opens too early you will have sneezing.

 

[Orkney seacrawler]

Facts first.----Compression test values must be posted.----And does spark jump a gap of 3/8" ( 1cm ) on both leads ?-----Fuel pump diaphragm checked ?----Water pump impeller replaced ?

Both cylinders was even on compression if I remember correctly I think they was about 120psi, I will do another compression test. And post the readings on here.
the spark does jump a gap Of 1cm Easily and I have replaced the impeller. I’ve not checked the pump Diaphragm yet.

 

[James R]

Sorry to hear about the hands. Mine are not too good but then I'm old.
Give us the compressions. You have sparks so if the compressions are good, and we don't know that yet, do what oldboat says. mix some fuel in a spray bottle and shoot it into the carb throats while turning the motor over. If it fires and continues to run as long as you spray,fuel supply is the issue. Carbs could still be the problem.

 

[Orkney seacrawler]

Hello gents, sorry for such a late reply I finally managed to have another look at the engine. I followed oldboat1 advice. The engine fires straight up and would continue to run with fuel being sprayed into the carb.

I have cleaned the carb and also put a carb refurb kit on the engine it is still the same problem no start unless you manually spray fuel in. I checked fuel is being supplied to the carb it has a good flow of fuel.
I’m at a loss now with this engine it’s driving me mad . Any more advice for me gents?? Thank you

 

[racerone]

In the bottom of the carburetor bowl you will find the high speed jet ( orifice plug )---It is about 5/8" long with 1/4-20 thread.------It is way inside there.----And are you pushing the key in while cranking it over ??----What starting procedure are you using on this motor.

 

[Orkney seacrawler]

hi racerone, I lift the choke lever fully up and push the key in when trying to start.

 

[racerone]

Test the electric primer valve function.----Sounds like it is not working as designed.----This primer is a valve.---It is not a pump.

 

[Orkney seacrawler]

When I push the key in the electric primer clicks and release a shot of fuel. Is this correct? Or should it be a continuous flow? until I release the key. Thanks for the help I really appreciate it

 

[racerone]

Once the pressure is gone nothing comes out of that valve.----When motor is cranking the pump puts fuel through this valve.----This fuel should pulse out of the primer valve when motor is cranking.

 

[oldboat1]

Take the cover bolt off the front of the bowl, and try to clean out the h.s. jet under there. Use carb spray first, applied using the plastic nozzle. See Racerone's post (#13).

 

[Orkney seacrawler]

Good evening gents, following all your advise I managed to get the engine running. The problem was a perished o-ring on the fuel primer. It’s still running abit rough as you can see from this video I will attach. Should water be coming from the exhaust. My mind is blown with this engine it’s drove me mad

 

[racerone]

Water should come out with the exhaust relief.-----Fact for you.-----You need to add 6" more water in your test bucket !