problem

[Venture driver]

1986 40hp evinrude .Cleaned carbs. Replaced all gas lines with clear ones. New primer bulb line. When I pump bulb up it gets hard and I can see gas at carbs. Cranks right up and idles. After a couple minutes I can see gas draining back from top carb. Shut motor off and pump gas back up. I let it set not running for awhile and the gas drains back again. Any ideas are appreciated

 

[jakedaawg]

Your bulb needs to be in generally upright position with the arrow pointing up.

 

[boobie]

Could also have a bad check valve in the primer bulb.

 

[F_R]

I suppose the theories concerning the primer bulb could be valid. However the primer bulb valves are only there for priming. If you are not actively squeezing the bulb they are not required to do a darn thing. Even if the were, most of them are crap at preventing back flow. The valves in the fuel pump would be more effective in preventing back flow.

Having said all that, there would be no back flow unless air is getting into the hoses somewhere. That air amount might be extremely minor and insignificant. Or otherwise.

To sum up, that's one reason why I don't like clear fuel lines. Too much angst over nothing. Maybe.

 

[F_R]

I can see it coming. Somebody is going to flame me for saying a leak may be insignificant. So, I hasten to explain: Suppose the float valve in that carburetor is not 100% absolute sealing tight. If so, and since it is above the fuel level in the carburetor, air molecules can enter that "leaking" float valve as gravity does it's thing to pull the fuel level down in the hose. No problem, the motor will start right up because the carb is still full of gas, and once running the fuel pump will replenish it as needed.

 

[Venture driver]

Thanks for the replies. I think I'll install a new tank and another new prime ball and see what happens.

 

[Chris1956]

Clear gasoline lines can be cheap vinyl. This can expand when it gets warm and start to leak at joints. Also, are those clear fuel lines rated for OB use?

 

[Venture driver]

Yes chris1956

 

[Bosunsmate]

Thanks for the replies. I think I'll install a new tank and another new prime ball and see what happens.

If you a having no running problems with it, you dont mention any i can see, then id put that money into fuel rather than just duplicating your current assets

 

[Venture driver]

Bosunsmate. It does crank right up and idles. I can see gas coming back from top carb. The idle changes when I squeeze the primer bulb and push gas back into top carb

 

[Bosunsmate]

Bosunsmate. It does crank right up and idles. I can see gas coming back from top carb. The idle changes when I squeeze the primer bulb and push gas back into top carb

Alright, What happens to the idle?
You definitely dont want a cylinder running lean

 

[Venture driver]

It idles up

 

[Bosunsmate]

It idles up

Yes definitely keep going getting that sorted, sounds like it is running lean then. Id lean on the fuel pump being the issue rather than further back than there

 

[glust]

I had a running issue once where the motor would run fine for a few minutes and then quit. After a few minutes it would start up fine, run a while and quit again. The fuel tank has a breather valve that keeps the tank from vapor locking like your new "safe" five gallon gas cans that burp all the time when they are gasping for air. I loosened the gas cap slightly until I got back to dock . It ran fine. Sprayed out the breather valve with starting fuild to clean out the gunk. good to go.