40 hp Johnson bogging down when throttled down

[Blackmon1995]

I have a 1988 Johnson 40 hp 2 stroke outboard. It idles and runs perfect until I throttle down. When I mash down on the throttle it will stutter and bogs down for about 5-10 seconds then it takes off and runs perfectly. I rebuilt the carbs about a year ago and it ran perfectly with no bogging down. I have recently put a new fuel pump plugs and plug wires on it and it hasn’t helped. Please help me I know it’s something simple i just haven’t figured it out yet.

 

[kimcrwbr1]

Have checked engine sync and link? Turn the slow needle out 1/8 rich counterclockwise and see if it improves? Adjusting the slow needle may help also confirm proper sync and link.

 

[Blackmon1995]

I have not but I will try that thanks

 

[kimcrwbr1]

It looks like you have fixed jets you may have to rebuild the carbs. Do both carbs open exactly the same time? There is a mark on the throttle cam the carbs should just begin to open as the mark on the cam passes center of the roller on the bottom carb.

 

[fdrgator]

You say it idles perfect until throttle down. That sounds like a contradiction. I am guessing you mean till throttllng UP (increasing speed). If so---

Disconnect the throttle cable from the motor, then with motor not running, operate the throttle with your fingers where the cable was attached (at motor), while observing exactly what happens. The timer base should start moving first, with very little movement of the carburetor shafts, until it reaches full advance (against the bumper). Only then, should the carbs open fully. If the timer base is sticky, and the carbs open too soon, it will stumble big time---maybe even stall & quit.

 

[Blackmon1995]

Yes when I throttle it up all the way is when it bogs down. Both the carbs open at the same time and I rebuilt them about a year ago.