1975 Johnson 25 HP Not Running

[z.fields27]

I purchased a 1975 Johnson 25 HP a few months ago with a few known issues. It was bogging down and the electric start quit working. My guess was that the engine needed some carb work and it would be a simple job. I couldn't have been more wrong. I checked compression and both were just over 100. I ended up with no spark, so I put in new points and condensers. This then led to me finding a cracked coil. So now the engine has a brand new ignition system. I went to fire it up the other day and it still won't hit. I have taken the carb apart and cleaned it which hasn't changed anything. The plugs are not wet at all after a few pulls, so it seems as if the fuel isn't making it into the engine. I have frustrated myself to no end working on this engine and don't seem any closer to solving the issue. If anyone that has any advice on it could help, it would be much appreciated!

 

[racerone]

Remove sparkplugs.----Put 6 -1/2 drops of fuel in each hole.----Install sparkplugs.------Pull on the recoil 10 times if needed.----Report what happens.

 

[z.fields27]

Remove sparkplugs.----Put 6 -1/2 drops of fuel in each hole.----Install sparkplugs.------Pull on the recoil 10 times if needed.----Report what happens.

Just ran out and tried this. It hit on the second pull and ran for maybe 2 seconds. I am assuming it ran until it didnt have any fuel left.

 

[racerone]

Repair your carburetor.----Inspect reed valves.----Check to see if choke goes closed and stays closed when attempting to start motor.----In my opinion this should be an easy repair.

 

[z.fields27]

What exactly do you think is wrong with the carb? I was going to take out the reed valves and look at them but im not sure what to look for when inspecting them. This is my first attempt at any work on an outboard so its been a learning process, i’m sure it is most likely a simple fix.

 

[Crosbyman]

small plugged up fuel channels in the carb will not allow fuel to reach the intake as vacum pulls or ... tries to pull in fuel.

what cleaning did you do ... did you flush all fuel routes , and blow dry . the side channel leading to the top is very narrow make certain it is clean and open

does fuel fill the carb bowl ? unscrew the bottom #46 nut to see if fuel drips out.

try unscrewing the top adjustment needle half a turn ccw choke and retry

you kind of proved the engine will fire.... it just needs the fuel to reach the cylinders. has suggested clean the carb...internal passages ... lots of utubes to show you how.


see older carb model... new ones work the same newer carbs have non adjustable orifices or jets .... all need to the cleaned .

 

[z.fields27]

small plugged up fuel channels in the carb will not allow fuel to reach the intake as vacum pulls or ... tries to pull in fuel.

what cleaning did you do ... did you flush all fuel routes , and blow dry . the side channel leading to the top is very narrow make certain it is clean and open

does fuel fill the carb bowl ? unscrew the bottom #46 nut to see if fuel drips out.

try unscrewing the top adjustment needle half a turn ccw choke and retry

you kind of proved the engine will fire.... it just needs the fuel to reach the cylinders. has suggested clean the carb...internal passages ... lots of utubes to show you how.


see older carb model... new ones work the same newer carbs have non adjustable orifices or jets .... all need to the cleaned .
View attachment 392347

What should the back butterfly on the carb be doing when trying to start the motor? Mine is closed off. Wouldnt that mean no fuel is getting to the engine?

 

[racerone]

Throttle plate has holes in it to allow air / fuel to go in at idle.----In neutral you open throttle until you hit the interlock.----Throttle plate should open slightly.----Ignore start mark on the grip.----Does choke go on and stay on when you try and start it.---Electric choke or manual choke ?

 

[Nordin]

Butterfly against intake manifold is the throttle, the butterfly at the carb intake is the choke butterfly.
The throttle need to be a little open when starting, choke butterfly closed when cold start just for some seconds to get fuel up from the carb bowl to the intake.
Throttle and timing advance need to be adjusted "throttle pick up point".
There is a line at the timing plate cam. The throttle roller should start to touch and open the throttle butterfly at the line.

 

[Crosbyman]

at the engine START position the plate limits the inflow of air leaving the crankcase vacum to be focused on pulling more fuel from the carb's upper idle section where 3 very small drip holes still allow fuel to be drawn into the engine to get it going

the front plate is the choke plate and at the beginning of the starting process it is closed allowing the crankcase vacum to pull all the fuel it can from the carb just to get it going.

when the engine starts the choke plate is open allowing more air to mix in with the fuel and vaporize it yet the back plate remains mostly closed to draw fuel from the top idle circuit. if that circuit is plugged up no fuel is extracted and the engine dies.

 

[racerone]

It should be an easy diagnosis and fix !!

 

[saltchuckmatt]

After you get it running with gas in the cylinders, try pumping the primer ball on your fuel hose. If it runs than your fuel pump needs help.

 

[z.fields27]

Throttle plate has holes in it to allow air / fuel to go in at idle.----In neutral you open throttle until you hit the interlock.----Throttle plate should open slightly.----Ignore start mark on the grip.----Does choke go on and stay on when you try and start it.---Electric choke or manual choke ?

It has a manual choke.

 

[z.fields27]

After you get it running with gas in the cylinders, try pumping the primer ball on your fuel hose. If it runs than your fuel pump needs help.

I can’t get it to run for any amount of time with the fuel in the cylinders. By the time I reached to get the primer it would already be shut off.

 

[z.fields27]

I again checked compression today, both cylinders were around 110. Checked spark, good bright blue spark on both cylinders. Pulled the carb out and cleaned it out, even though it doesnt appear to be dirty. While I had the carb off I pulled the intake manifold off and checked the reed valves. There didnt appear to be any cracks or damage to them. At this point I was concerned that they weren’t opening right since there is no gas at all getting to the cylinders. I pulled on the engine a few times to try and check the vacuum on the reed valves, it didnt appear that they were opening althought I an not sure if this is the correct way to go about it.

 

[racerone]

When you pull the choke on does the choke plate close fully ?----And does it stay closed after you try and start the motor, yes or no or no idea what to look for ?

 

[saltchuckmatt]

You need to diagnose the fuel pump before diving into all of this. Put drips in the cylinder but use a small spray bottle of fuel (50 to 1 fuel) to keep it running (throat of the carb) and then start pumping the ball and see if it runs.

It's either fuel pump, carb related (not cleaning it correctly or defective) or it could be crank seals.....yada yada yada

 

[z.fields27]

When you pull the choke on does the choke plate close fully ?----And does it stay closed after you try and start the motor, yes or no or no idea what to look for ?

The choke does close fully. It also stays closed while I try to start the motor.

 

[z.fields27]

You need to diagnose the fuel pump before diving into all of this. Put drips in the cylinder but use a small spray bottle of fuel (50 to 1 fuel) to keep it running (throat of the carb) and then start pumping the ball and see if it runs.

It's either fuel pump, carb related (not cleaning it correctly or defective) or it could be crank seals.....yada yada yada

I tried to use a spray bottle earlier today through the carb to try and keep it running, however it was not successful. I got curious and pulled the plugs and they were not wet at all. I have also rebuilt the fuel pump since I got the engine. I disconnected the hose from the carb and when I pull on the engine fuel comes out of the hose.

 

[saltchuckmatt]

Remove sparkplugs.----Put 6 -1/2 drops of fuel in each hole.----Install sparkplugs.------Pull on the recoil 10 times if needed.----Report what happens.

By the way Race, please explain how does one put in one half of a drop?!