1989 Johnson 120HP outboard stalling

[ajahman]

Hi guys,

I need some advise on a 1989 120HP Johnson Outboard.After running at 4200RPM for about 15 min I start to loose power and the engine surges and then stalls.I live on a saltwater creek and it takes about 15 min to get to the sound where the water is usually more choppy.The stalling occurs about the same time and location, I.E after 15 min run time AND just when I enter a choppy sea.I opened the fuel fill cap to see if I had a vent restriction but the engine still stalled. When I disconnect the fuel line from my aluminum below deck fuel tank and connect it to a 6 Gal portable tank the engine runs fine...no stalling or surging.Back at the dock I disconnected the fuel line from the below deck tank and pumped fuel into a mason jar to look for water.Minimal water and some trash.Fuel flow from hand pumping was good ..no apparent restriction or massive amounts of water or trash. Any ideas? I appreciate any thoughts on how to test my fuel/air supply system.
Thanks.
Ajahman.

 

[fshrgy99]

Re: 1989 Johnson 120HP outboard stalling

Siphon all gas from tank through a funnel fitted with a filter screen. Check for debris. Rinse and repeat til clean. Any debris in fuel is a recipe for a stranded day on the water. Your fuel filter will clog, your fuel pump will clog, your carbs will clog, your cyls with restricted fuel flow will overheat, you may melt everything, everyone will blame the vro! Run with a clean portable tank til resolved. My .02

 

[mekkamaz]

Re: 1989 Johnson 120HP outboard stalling

I back that up too. You have find the issue by connecting the portable....also check all your hoses and see if they need to be cleaned / changed. look for any crack that might let air enters the fuel sistem. As fshrgy99 says, run portable til everything check and solved, or you can damage your engine. Best regards.

 

[toddschubert]

Re: 1989 Johnson 120HP outboard stalling

You can buy a clear in line filter for around $20 I got mine at Academy. It helped me with a problem when I bought boat from p/o and had no idea what condition fuel was in. I saw debris and had to drain tank completely. I ran a high concentration of seafoam and oil for a while and it cleared up

 

[ajahman]

Re: 1989 Johnson 120HP outboard stalling

Thanks for all of the replys fellas.I appreciate the info.Contaminated fuel is kinda what I thought it might be but wanted to get learned advise from folks more outboards savy than Myself.When I siphon out the tank,how would I Clean the inside of the tank?Flush with fuel,alcolol and re- siphon till clear?Thanks again.

 

[CharlieB]

Re: 1989 Johnson 120HP outboard stalling

The dip tube in a tank does not reach all the way to the bottom, it 'stands off' a 1/4 inch or more so as to not suck up accumulated water and trash laying under the fuel.

Once you hit rough water and the boat starts rocking, mixing the bottom layer of water with the fuel, that's when you start having low speed problems.

First order, install a spin-on water separating fuel filter to pull any water out of the fuel to the motor. This is a preventative measure but will not cure a soggy tank.

Hopefully the tank is not full, if it is, siphon out most into clean containers. Jack and block the trailer such that the fuel level sending unit is over the lowers quarter of the tank. Leave the boat sit like this for a day to be sure all water settles to the low quarter.

WARNING, beware of FUMES. NO SMOKING< SPARKS< ETC

Remove the fuel sending unit, cut a small V notch in the end of a siphon hose such that the hose cannot suck itself and seal against the bottom. Weight the hose by screwing on a nut or two that just fit snugly onto the hose, this will help hold the hose down in the tank.

Suck/siphon out the water and trash from under the fuel until you are pulling clean fuel from the lowest point tin the tank.

Reinstall the sending unit with a new gasket. Double check for leaks.

Make sure all fumes are well vented away.

 

[water world]

Re: 1989 Johnson 120HP outboard stalling

install clear fuel hose at engine. run engine and if it has bubbles in it you have a air leak in fuel system