2000 40hp Johnson won’t open up under a load

[Jld1983@att.net]

Hi, I have a 2000 Johnson 40 hp (J40RLSSM) that started running rough last summer. I was running the boat down the lake and it suddenly lost power. It never died just lost power to run over 5mph. After restarting it would take off again and run fine then after a few minutes do the same thing. I looked under the hood and the fuel pump was leaking a little so over the winter I rebuilt the fuel pump. Took it out this spring and it would open up for about 5 seconds and then lose power again. I can turn the motor off and fish for about 30 minutes, start it up and it’ll take off but only for a few seconds then lose power. I used a light to watch the fuel flow into the carbs when it started acting up and it seems to have no change with the motor acting up. I replaced the plugs, wires, and coil. I checked the compression 120 psi on both cylinders. Put a spark checker on it and have 7/16 spark on both cylinders. Was going to replace the power pack next but was hoping for some advice before I did that. Any help would be greatly appreciated.

 

[racerone]

Check the flywheel key.

 

[Jld1983@att.net]

Is there a simple way to check that without removing the flywheel?

 

[jakedaawg]

After verifying flywheel key:

1. Make sure it's not overheating.
2. Maybe with a timing light verify spark on both cylinders while it's acting up.
3. Have someone squeeze bulb rapidly while it's acting up.

 

[Jld1983@att.net]

It’s not overheating. I’ve tried pumping the bulb and it stays hard with no change to performance. It seems to idle good until I begin to give it some throttle. You can almost immediately hear it start bogging down as soon as you pass a certain point in the throttle

 

[jakedaawg]

Is the timer base moving as you advance throttle? I take it flywheel key was fine?

 

[Jld1983@att.net]

I checked the flywheel and everything seemed right. There was no play at all to suggest a broken or worn key, however, I did not take it apart to inspect it visually. Yes, the timing base does move with the throttle.

 

[racerone]

A new powerpack can usually fix these problems.-----They are cheap and it is worth a try.

 

[tramsdell]

Clean the carburetor, or pay someone WHO KNOWS WHAT THEY'RE DOING to clean the carb.

 

[jakedaawg]

I checked the flywheel and everything seemed right. There was no play at all to suggest a broken or worn key, however, I did not take it apart to inspect it visually. Yes, the timing base does move with the throttle.

A sheared key shows no outward evidence. The only way you can tell is by popping the flywheel off. It's not rocket science super easy just one nut

 

[jakedaawg]

Verify that the arrow on the primer bulb points towards the motor

 

[Jld1983@att.net]

Primer bulb is installed correctly. I don’t have a socket big enough to removed the flywheel so I am going to pick one up tomorrow and then inspect the key