Bubbles in fuel filter

[Bitmess]

1995 130 Johnson. Runs good until WOT. I see a flood of bubbles in my inline filter when I open up the throttle. So much air that the filter is only half full. The filter is between the primer bulb and fuel pump.
Motor will start surging. I slow down and bubbles disappear and runs pretty good. I have a new fuel pump. Replaced the VRO with the old kind. It was doing this with the VRO also but was getting rubber chunks in the carbs. Some post say bubbles are normal. Now I'm Confused. Are bubbles normal? Is the air causing my issues. Common sense tells me air in a fuel line is a bad thing. I don't know?
Help please.
Kenneth

 

[Outsider]

Re: Bubbles in fuel filter

Air bubbles aren't normal. Try removing the in-line filter and see what happens. I'm betting it's causing the WOT problem ...

 

[F_R]

Re: Bubbles in fuel filter

Air bubbles aren't normal. Try removing the in-line filter and see what happens. I'm betting it's causing the WOT problem ...

Yep, perhaps the filter itself is the problem. May be too restrictive. Try running without it. A fuel pump pressure/vacuum gauge is a great tool for diagnosing such problems. And they don't cost very much at Harbor Freight.

 

[Tim Frank]

Re: Bubbles in fuel filter

1995 130 Johnson. Runs good until WOT. I see a flood of bubbles in my inline filter when I open up the throttle. So much air that the filter is only half full. The filter is between the primer bulb and fuel pump.
Motor will start surging. I slow down and bubbles disappear and runs pretty good. I have a new fuel pump. Replaced the VRO with the old kind. It was doing this with the VRO also but was getting rubber chunks in the carbs. Some post say bubbles are normal. Now I'm Confused. Are bubbles normal? Is the air causing my issues. Common sense tells me air in a fuel line is a bad thing. I don't know?
Help please.
Kenneth

1) If you were getting rubber debris in the carbs, you have fuel lines that are deteriorating...you need to trace and fix.

2) You need to make sure that what you are seeing are really air bubbles. if so, the fuel pump will lose some suction and you will not get full fuel delivery. Check all joints, and per 1) check hoses internally for rubber break-down.

3) The bubbles could well be just gasoline vaporising under the reduced pressure in that suction line. Some bubbles would not pose a problem...if it was not for the clear section of the filter, you would not even know they were there. Too much bubbling, and it can be a fine line, and fuel flow can fall below what you need and it will impact the performance of your motor.
As suggested, after ensuring that you don't have a leak that is allowing air ingress, try removing the fuel filter and see what happens. If the performance issue goes away, it's telling you that you would need to up size your fuel line size if you want to run an inline filter....or just run without it, your call.

 

[Tim Frank]

Re: Bubbles in fuel filter

Air bubbles aren't normal. Try removing the in-line filter and see what happens. I'm betting it's causing the WOT problem ...

Air bubbles aren't, some minor fuel bubbling is..... It's basic vapour pressure chemistry.
OP has to determine whether he has a leak or too small diameter fuel line.