Johnson 4 HP sync issue?

[djmeaney]

I?m still having a problem with my motor, a 2000 Johnson 4 HP long-shaft, accelerating. It accelerates fine when cold, but after running more than a few minutes it will stall after when accelerating unless I back the throttle back to low speed. The primer bulb is still firm when this happens, and squeezing the bulb has no effect on the motor.

I did notice last night when running it in a test barrel that if I quickly pull out the choke and push it right back in (the same motion without stopping) when it first starts to stall during acceleration that the motor will ?catch? and will stay running at the higher rpm with the choke in.

Here?s what I have done so far:

• rebuilt the carb (with a kit)
• flushed the fuel lines
• replaced water pump
• pulled cylinder head and cleaned water passages (weren?t clogged)
• removed exhaust housing and cleaned water passages (weren?t clogged)
• new spark plugs
• tested spark with 3/8?s gap on testing tool (no problem)

I haven?t tested compression yet. However, I am thinking that the problem may be ignition/carb synchronization. Does that sound like a possibility? Any other suggestions, aside from testing compression?
Thanks,

Dan

 

[AlTn]

Re: Johnson 4 HP sync issue?

the roller on your carb linkage should rest on the timing cam plate which is attached to the armature plate...in the Start position the roller should rest on a mark on that timing cam plate...is this position, your carb butterly should just begin to open...as you advance the throttle handle, the roller should open the carb plate to exactly horizontal at wot...your symptoms sound more like your main jet is still clogged some

 

[djmeaney]

Re: Johnson 4 HP sync issue?

I did set the carb linkage and things seemed to improve a little. I don't have the service manual in front of me, but there the next step in synching calls adjusting the initial (ignition) timing by screwing the spring load adjustment screw finger tight until the spring is collapsed and then backing out 3 full turns.

I'm keeping a positive attitude that this may be misadjusted and that along with a more detailed carb sync it'll resolve the problem. (But I'll be prepared to remove the plug for the calibration core to really inspect the main jet). I have yet removed the plug in this round of troubleshooting.

 

[djmeaney]

Is this normal fuel valve operation?

Is this normal fuel valve operation?

The sync didn't solve my problem. Still wants to stall when throttle is opened up, unless I quickly pull the choke out push right back in.

This model has an integral fuel tank and the connectors for an external with a fuel valve to switch between the two. The integral fuel tank is not hooked-up because I want to replace the in-line fuel filter. So the fuel line from the carb to the integral tank is still connected, but blocked off.

After testing the motor tonight, I decided to let it run out of fuel so I moved the fuel valve to the integral tank position. It ran for more than five minutes at 1/4 to 1/2 throttle and never ran out of fuel. It took a few more minutes after the external fuel tank was disconnected before it finally ran of fuel.

Is this normal? Is something wrong with the fuel valve? Both o-rings in the fuel valve have been replaced. Could this be part of my problem?

Dan