Gas tank venting, 6.3 gallon tank for 1970, Johnson 60 hp

[looncommander]

I recently had a minor tune-up performed on my outboard engine. First trip to the lake the motor ran fine at WOT for about ten minutes then suddenly quit. This is a repeat problem and one of the reasons the engine went in for a tune-up. Upon inspecting my fuel tank gas cap, I found that it has two very small vent holes, which open only after loosening the knurled knob and o-ring on top of the filler cap. (I think it is one of the many California regs trying to reduce vapors from fuel tanks)

Does anyone think that these two small vents are not providing enough air to allow for the fuel pump to pick up enough gas to continue running WOT?

 

[GA_Boater]

The vent screw has been around far longer than California's vapor reduction regs, Tanks have been vented like this since portable gas tanks were first used.

Easiest way to find out if the vent is the culprit is to loosen the gas cap. If it continues to die, it isn't the gas cap vent.

 

[F_R]

As said, test your theory by loosening the cap.

 

[Scott Danforth]

I have to ask the obvious - you do have your vent open when running, correct?

 

[steelespike]

If the vent didn't work the primer bulb would collapse.

 

[gm280]

You didn't state if the engine cranks back up after the ten minute run and shut down. If it does, then that could be the vents are not open clearly. Could be some crud in the vents not allowing enough air and the engine stops because it is starving for fuel. When it stops, do you have to reprime the inline primer bulb to get it to crank up again. Let us know. JMHO!

 

[looncommander]

Thanks everyone. Yes, the vent cap was opened. I cannot describe the primer bulb as being flattened but I would say it wasn't "plump" either. The boat did restart after waiting a few minutes which included squeezing the primer bulb as well. On the trip back to the dock, I went to WOT for only a few seconds before the engine started to cut out again. I reduced the throttle back to 3/4ths or 1/2 and gingerly made my way to the dock.

I'll try loosening the cap next time out.

 

[oldboat1]

haven't seen or used that cap assembly, but the valve under the cap apparently has a manual release -- looks the same as the valve on top of my shop air compressor. I'm guessing, if you pull that valve open from the bottom you could clean it (would try some carb spray). It sounds to me like that vent might be failing or just needs cleaning. When you squeeze the bulb and release, fuel enters the bulb upon release if the venting is working right. If the bulb doesn't fully recover (regain it's shape), think the venting is suspect. Might try cleaning the valve.

 

[Faztbullet]

Its not a fuel or venting problem, sound more like a problem with ignition system such as pulse amp or coil. Check out the ignition system since it was doing this before and after the repair was performed. What exactly did they do in tune up as point setting is critical on this engine....

 

[82rude]

An often overlooked part is the connectors at either end of the tank and hose with particular attention to the one that plugs into the motor.They can be loose or faulty.Happen to me with similar symptoms to what you had and drove me bananas.

 

[racerone]

Describe what was done on a " minor tune-up "--------Was flywheel removed ?