1979 Johnson 70 horse engine with idle problems

[marcusknight]

I have a 1979 Johnson outboard engine and it's had some problems stalling out at idle speed. It's been hard to determine what it is but someone today at a shop suggested that it could have something to do with the fuel delivery including perhaps some sort of gasket or some type of ring just inside the engine where the fuel comes in. I have also wondered how long the fuel tank hoses are good for. Mine has been on the boat since at least 2007 when I bought it so naturally I am thinking of replacing that.The idle speed on the tach seems to check out when I have it in idle and all that so for the moment I am not concerned about that part of it. I've also been thinking of running a load of seafoam through the whole few system, but I'm not sure if I should run seafoam through the engine before or after I replace the fuel hose. any thoughts on any part of this? note that the spark plugs are brand-new and they're the same factory specified spark plugs I have always used. they are L77JC4.

Also, does anyone have any thoughts on the old OMC fuel tanks with the black Cap that doesn't seem to have any place for a vent on it? Do they vent after all and maybe something on the Cap is clogged that I could clean, or are these tanks supposed to be entirely sealed all the time because every time I open it a big gush of air comes out especially on a hot day.

 

[boobie]

First thing to do is check the compression on it.

 

[racerone]

When the hose is not attached and the cap is tight , the tank is sealed.--------See the 2 wee pins where the hose plugs onto the tank ?----Those are valves and one lets the fuel out and the other is the vent.

 

[marcusknight]

I had the compression tested. It was well within specifications.

 

[boobie]

Do a good decarb on it using BRP Engine Tuner. Follow the directions on the can.

 

[emdsapmgr]

It's possible to stall if the idle is too low. What is the idle rpm in gear? The idle needs to be set when the boat is floating normally in the lake and the engine is running in forward gear. Last time the carbs were apart for cleaning?