Do I need the check valve on built in tank?

rdhutch4

Cadet
Joined
May 15, 2009
Messages
10
1996 Johnson 115 on 18' Bonita with fuel tank mounted in bow. Recently replaced all fuel lines and water separator. Engine runs and starts great. After turning off motor for very short time, it restarts with no problem. However, if it sits for a few minutes, like when fishing a spot for a few minutes, when I start the motor to move to another hole, it runs like it is missing until I get up to 4000 rpm. Runs great to next hole, where I again kill the engine. If I crank it right up, it runs fine. If we sit there a few minutes, same problem. I am suspecting a bad fuel pump, but am also curious about the check valve which was removed by my mechanic a few weeks ago. Will the lack of the check valve allow all fuel in the lines to drain back to the tank ( I ask because I noticed after sitting for a few minutes the primer bulb is empty)? My theory is that the check valve is allowing the fuel lines to empty and relieve any required pressure, and that the fuel pump is weak (going bad) and has difficulty drawing sufficient fuel for take off, until the pressure of high rpm's pulls adaquate fuel into the lines. Any opinions?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: Do I need the check valve on built in tank?

After an engine once starts, the primer bulb does not remain hard. Remember -- fuel is being sucked through it, not forced through it. Fuel should not run back to the tank since the primer bulb has check valves in it -- although not very good ones. IF and I repeat IF, the fuel tank can siphon due to a fuel leak anywhere in the system you definitely NEED that anti-siphon valve. I don't think that is your issue with engine operation. A carbed engine has enough fuel in the carb float bowls to enable restart.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: Do I need the check valve on built in tank?

If the primer bulb is empty after sitting while fishing, it needs to be replaced. I agree with Silvertip, that is probably not your issue, but try it first and post back results.
 
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