Fuel System Question for 85 Johnson 115

[ulmatms]

I am having a sort of fuel problem but not sure where to begin. About the running of my motor. <br /><br />1. Idle has problems but usually stays running.<br />2. High idle to WOT the motor sound like it is running perfectly (5800 RPMS @ WOT).<br />3. Back to idle and it sound like it wants to die.<br /><br />Carbs have been cleaned and rebuilt twice in last 3 months. Compressed air, soak, more compresses air, etc... Now here is what i am asking about. While the engine is in idle the fuel bulb will SLOWLY get softer and softer but usually not to the point of the engine running out of gas although it does seem to happen every once and a while. At WOT the bulb seems to stay firm. Once back to idle however the same thing above happens. Now, if i completely shut off the motor and wait say 3-4 min. The primer bulb seems completely empty and all of the gas seems to have back fed back into the gas tank. I have to give it 2-3 GOOD sqeezes before i hear a click from my fuel pump meaning the gas is finally back to it. I guess that's what that click means anyways. <br /><br />So i guess to summerize, the higher the RPMS the firmer the gas bulb is. So my question is where should i start in tring to figure out this weird problem. I just don't want to go buy all new parts and replace everything because money is not on my side right now :-( <br /><br />Any help would be appreciated. Thanks in advance.

 

[Barnacle_Bill]

Re: Fuel System Question for 85 Johnson 115

There is a check valve in the primer bulb so it will only pump one way and hold the fuel you have pumped up. Actually at WOT, the bulb should go a little soft as fuel is running thru it. I would replace the primer bulb and go from there. Remember, the arrow on it points towards the motor.

 

[ulmatms]

Re: Fuel System Question for 85 Johnson 115

Sorry for taking so long to get back to this. Work has been horrible lately.<br /><br />You are right, the bulb firms up in the mid RPM range and does get a little soft @ WOT.<br /><br />Finally got back to working on this and have isolated it from after the fuel filter to the carb. If i plug up the exit point of the fuel filter it holds firm. I have replaced every hose from the filter, through the VRO pump (plugged off @ oil nipple and ran pre-mixed), to the carbs, and the vacume hose going to the VRO pump. Now i think this might have been a two part issue. With everything replaced hose wise, i can pump up the buld hard untill i can't squeeze anymore. I see no dripping or anything comming for any of the connections. So i started it up, cranked up nicely and idled better then it has before, but i noticed that in the fuel filter (clear case), there was more and more air filling up the filter untill it reached a certain point close to the bottom of the fuel filter. At that point the idle got rough again and the buld was squishy. If i pumped up the bulb and kept it that way the idle seems better, but when i didn't touch it for a min the same thing above happened.<br /><br />The ONLY part of the fuel system, besides the carbs, that i haven't replaced is the VRO pump. $$$ OUCH!! Can a bad fuel pump inject air??<br /><br />NOTE: I did use a clear gas line to go from where the gas tank conneced to the outboard to the fuel filter. I saw no air in the line while running to make me think the air is coming from that direction. Everything points to the air back feeding to the fuel filter. And @ mid to high RPMS the fuel filter actually fills up some and then goes right back down when you throttle down to idle.<br /><br />Unless it is the fuel pump i am at a total loss as to where the air is comming from. <br /><br />Thanks for the help!!!

 

[R.Johnson]

Re: Fuel System Question for 85 Johnson 115

Are you running from a built in fuel tank, and have you checked the anti-siphon valve. A service manual will tell how to check these systems. With out a manual, you are groping in the dark. When the engine is running, the primer bulb is nothing but a wide spot in the fuel line. How can it stay firm if fuel is being drawn through it? Fuel is being drawn, not forced. That bulb should be neutral, neither firm, or sucked in. The bulb with it's check valves pump fuel to the empty carb's for start up. From there on, there should be a free flow of fuel. That fuel pump will only deliver about 2-4 lbs. of pressure, at not more than 2-4 in/lbs of vacuam. The service manual explains all of this