Fuel Return Line Question..

[Rick]

Ok. Bike is up and running for a few weeks now. About ready to put plates on it. But I seem to be having a fuel delivery problem. I asked once before about routing the fuel return line.
I did NOT route it back to the tank. Instead, I sent in to a small aluminum bottle, figuring if it every got close to filling it, I could just dump it manually. That was the plan anyway. The bottle is mounted low, against the frame rear downtube.
Engine runs OK for a while, then starts starving for fuel. If I pull the supply line off, it's empty. I was running an inline filter, as well as the screen in the tank. I have since removed both of them, but still have the same problem.. Which got me thinking.. (a dangerous thing) and I re-read my earlier post about fuel lines...
Saw someone mentioned that on the clone engines, the return line does dual duty, serving as both fuel return line, and air bleed. On my original engine, the return line was plumbed into the tank fairly high.. so my thought is that any air bubbles in the system would rise.
Now... my "catch bottle" is mounted fairly low. (I DID vent it, too)
Is it possible that since it's now lower than the injector, that any air that gets in the system CAN'T bleed out? And perhaps forms a lock in the line?
If that's so, I should be able to temporarily mount it higher, and see if it makes a difference..
For the record, I KNOW it's something that I'M doing wrong. I ran it for several weeks on the small engine mounted tank, and never had the problem...
I'm just looking to pick someone's brain here. Thanks..

[Byrdman]

I think you're correct on both accounts.

I would caution however that many diesel engines use the return fuel as both a fuel injector lubricant and for fuel injector cooling. These engines have a bunch of extra return flow for that reason and a small "Catch bottle" might get filled up very quickly.

[Nanko]

The bottle is mounted low, against the frame rear downtube.
Engine runs OK for a while, then starts starving for fuel. If I pull the supply line off, it's empty.

Rick
If your catch bottle is mounted below the fuelpump , the fluid level column will create some underpressure , if there is any leak in the circuit , air will enter ,making the engine starve.
Try again with the bottle mounted hihger than the fuel pump.

Nanko

[Diesel Dave]

Rick,

Return lines need to have a head of fuel to prevent back surge pulling air into the back of the injector, it should also allow any air bubbles to rise through and escape.

Raising the bottle will help but you may be surprised by the volume of fuel that gets ejected - it would be better to solder a return fitting into the tank.

If you fit a clear feed line to the injector you will see the surging if there are any bubbles present.

Hope this helps
Dave

[Nanko]

If you dont like to drill an extra hole in the tank for the return line , you could create a co-axial connection . If this is a banjo coupling , drill a hole in the banjo " bolt" ,( silver ) solder a small coppertube which should end few inches above the bottom , so airbubbles dont mix with the feed line.

Nanko

[Rick]

All is good once again.. but I don't know why.

Drilled a small hole through the fuel tank cap, and brazed a small section of tubing into it. Made sure to keep the tank vented, too. Disconnected my previous "catch bottle"..bled it out, and started it up. Took a few minutes running to clean all the air out of it... and it's fine now.. Funny thing is, there was NO fuel in the catch bottle. and after riding it 6 miles, there didn't appear to be any fuel coming back through the new return line set-up either..
But it works!
Thanks for the assistance, gents.

[Ih8Suvs]

Ok, I know you aren't supposed to tee into the supply line for the injector return, but the set-up in the attached picture is working fine. I just can't bring myself to braze a nipple into the tank until I am ready to repaint the tank sometime down the road. The filter positioned as shown serves as an air seperator. In fact, the bubble you see in the filter has now migrated up and out into the tank. This picture was taken before all the air from installing the filter had a chance to migrate out. No bubbles from the return line make it down as far as the filter. At any rate the bottom of the filter has clean air free fuel. I have had zero fuel delivery problems with this set up in a little over 2000 miles.

[Byrdman]

"if it ain't broke, don't fix it"

With the setup shown, any return air would eventually run it's way back to the tank. I think the problem most people have is simply because their setup isn't as perfectly vertical as yours. When the air moves to the highest point, it tends to be in a filter or a fuel line, not the tank.