1990 140 hp Johnson fires up and dies.

[saddlebandit]

I have a 1990 140 hp Johnson when I bump the key its starts and then dies right away. It fires right off but than that's it like its getting the initial squirt but nothing else. It started doing this last season but than started working fine. I ran all the gas out and let it sit in the garage all winter now with fresh new gas and bulb primed its happening again even when I keep priming bulb.

 

[daselbee]

Re: 1990 140 hp Johnson fires up and dies.

Idle fuel circuits are clogged. Get carb kits first.

Start at fuel bowl. Small brass tube extends down into the bowl. Clean it out. Run a wire up thru there. The top is smaller than the bottom of the tube. You can see the wire end when it comes out behind the metal side plate. Suck on the tube to judge air flow. You can feel air flow on your tongue better than if you blow thru the tube. Make all four the same.

Move to throttle bodies. There is a small welch plug on the side of each throttle body for each cylinder. Round, smaller than a dime, metal plug. Remove the plug, and look deep into the pocket. There are very small holes down in there. Maybe 5 or so for each pocket. Be sure you can see light thru each hole. I use welding tip cleaning wires for this job.
That pocket is called the calibration pocket. Install new welch plugs.

Re-assemble, do link and sync, start.

 

[saddlebandit]

Re: 1990 140 hp Johnson fires up and dies.

Thanks I already have the rebuild kits. I was holding off doing this since I've never rebuilt one before. Thanks for you expertise.

 

[daselbee]

Re: 1990 140 hp Johnson fires up and dies.

It is easy. You gotta do the throttle bodies too. That is a must.

Remove the welch plugs by drilling a small hole in the plug, screw in a sheet metal screw, and pull plug out. DO NOT RUN THE DRILL IN TOO DEEP! Easy does it.

Reply with questions as you go. Easy. Link and sync....start it up.

 

[saddlebandit]

Re: 1990 140 hp Johnson fires up and dies.

How can all four do this at once, and like last year just start working and then stop? The engine was running pretty good last yr except every once in a while.

 

[daselbee]

Re: 1990 140 hp Johnson fires up and dies.

Who knows? I don't know your engine storage procedure. Maybe gas left in the carbs thru the winter. Dunno.

But, If it fires, and then dies, it is a sure sign the idle circuits are clogged.

Try this as a test....rotate the red lever on the primer solenoid to the manual position. Start the engine, and before it dies, try to rotate the red lever back a little to find the sweet spot where just enough fuel leaks past the primer solenoid to keep it running. You follow?
You will be supplying fuel thru the primer solenoid system, bypassing the carb idle circuits. It will run like that, but it will be crappy. It will prove out whether the idle circuits are clogged.

Oh, by the way, when you are in the carbs, especially the throttle bodies, inspect those holes carefully. Verify that they are closed up. Find that defect. Don't just blast it with carb cleaner and not really find exactly what the problem was.

I had a 25 Merc in the shop last week. Single carb. It would start, run for about 20 seconds, slowly die away, and stall.
I pulled the carb, opened up the calibration pocket area on that carb (they all have something like that), and found two tiny holes, and sure enough one of them was plugged solid. Use the wire, carb cleaner, reassemble, start and run. Woo hoo...

Those holes are typically very very small, like about 5 thousands in diameter. They pass gasoline through to the venturi bore, right at the throttle butterfly. You can see them if you look very carefully, from inside the venturi, coming thru the wall.

 

[Bosunsmate]

Re: 1990 140 hp Johnson fires up and dies.

good tip on testing idle circuit daselbee