ScottMcM

My Feedback: (66)

I'm getting bubbles in my fuel. I had to mount the pump BEHIND the fuel tank, in the same area as the servos, because there is simply not enough room in the engine compartment (GP Ultra Sport kit). I flew the plane with a different engine, and didn't have any problems. The new engine (Fox 60 rear exhaust) needs a pump, where the old one didn't. Is there anything in particular that can make bubbles in a pumped system?

Jetdesign

My Feedback: (8)

From what I remember, the length of tubing from your case to the pump is not supposed to exceed 4 inches. Not sure how this would affect the system with respect to bubbles exactly, but the the reason for this is to minimize pressure loss due to air line expansion. Maybe you're getting some irregularities because of the long air line?

Are the bubbles forming in the tank? Or are they forming at the pump?

You have a vent line from the tank to open air, and are not using pressure from the muffler, correct?

...just trying to get some ideas flowing...

ScottMcM

My Feedback: (66)

Yep, i've got a vent open. The bubbles are forming at the pump. I'm trying something a little different. I pulled the tank out, and mounted the pump just behind the firewall, then slid the tank in behind the pump. Maybe this will work better.

Ed Smith

From the beginning.

Is the pump the VP-30 regulating pump?

Are you using crankcase pressure with, as previously stated, a no longer than 4" pressure line.

You should not be using muffler pressure.

Have you tried altering the hex adjustment screw?

Are the bubbles between the tank and the pump, or the pump and the engine.

Ed S

JohnBuckner

My Feedback: (1)

Also in addition to what Ed Smith outlined above if you have the VP-20 Ossilating pump it cannot work like that it must be mounted directly on the engine backplate or engine mount and the inlet/outlets must be mounted inline with the plain of rotation of the propellor.

John

ScottMcM

My Feedback: (66)

This is the pump that uses crankcase pressure. The bubbles are between the pump and engine. My line was much longer than 4", and I think that may be/have been my problem. The only way to shorten the line was to put the pump in front of the fuel tank, inside the fuse, which moved the tank back an inch or so. Previously, the pump was behind the fuel tank, and the line was nearly 8". There is absolutely no room in the engine compartment to mount the pump. I'll run it again tomorrow and let you guys know how it goes. Thanks for your help.

ScottMcM

My Feedback: (66)

Problem solved. No more bubbles. Moving the pump did the trick. Thanks guys.