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Air leak in fuel line?

N

Nrkdn

Member
I have a 1998 90HP Johnson Outboard. After I prime the bulb and it is solid, the engine starts and runs. However, if I shut it off for a few minutes, the bulb has air in it and needs to be re-primed. 18 gal external tank. Problem worsens as tank empties. Replaced fuel line to bulb and bulb. Is there an air leak somewhere after bulb? Or is it in fuel pump? Not a mechanic, but learning.
 
Yes, that is to be expected. However the bulb has air in it and requires more than couple sqeezes. Gas line comes out of top of tank and has new anti-siphon valve. Can hear it operate when priming. If no leak, how come bulb has air in it? Tube to bottom of tank, checked fuel line to engine (but not to carbs)
 
You are sure it is air ?-----Or is it fuel vapour ?------After all this motor does have a wee vapour seperator pump on it.
 
No, not sure. I do not notice any fuel leaks or fuel odor. So you could be right. Primer bulb hangs vertically from fuel tank (siphon effect). As fuel is used from tank, problem increases. Wonder if moving primer bulb down fuel line would help. Previous reply mentioned bulb softening. Purchased stronger bulb since previous softer one would collapse. So figure fuel pump is ok.
 
If a primer bulb collapses there is a problem between the bulb and the tank.-----Blockage in the tank pickup tube or a venting problem.
 
Do you have to prime it every time you start it even when warm? Are you having performance issues. After the initial cold start you should not have to pump the primer bulb or choke it unless the engine fully cools down. If you have to prime the carb every start the float is probably set too low.
 
The fuel should never siphon back into the tank have you replaced all the fuel lines? All it take is a tiny air leak for the system to drain back into the tank. Get a rebuild kit for the fuel pump and replace all the fuel lines in the motor and take it from there.
 
Are the screws for the fuel pump and mount snug and even? From the oil pump there is a check valve just before the wye are the hoses nice and soft and tight? Replace any fuel ine that is hard or cracked. My guess is you just have a tiny leak at one or more of the fuel line fittings. Zip ties work good for clamping the ends of the hoses.
 
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Replaced everything between tank and engine except tank appreratus. New anti-siphon valve and stiff primer bulb. Added a fuel filter also. but caused liner in fuel line to clog it. That was removed and repaired. Fuel line ok to splice entering engine.
 
Sounds good. Unable to see into engine as it is mounted on pontoon boat in a slip. No trailer to take it out of water. Use service to remove and store. Will try to reverse boat in slip and look again.
 
Right, checked yesterday. Must be fuel line leak between fuel pump and exterior part of fuel line. Fuel isn't siphoning back to tank but must be dripping out of leak somewhere inside engine compartment and is replaced with air from that spot.
 
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