Fuel injection return line

[desertrefugee]

A question for the fuelie gurus out there:

I had intended to run the return on my project Voyager into a separate port under the tank - into what was originally the Zyphyr fuel float hole. I could still do that, but positioning won't be ideal. My question is would there be any reason I couldn't (or shouldn't) just plumb the return into the supply line? Would this introduce air or alter the gravity delivery characteristics?

 

[Ansimp]

When you say the supply line I assume that is before the pump. I haven’t tried it but would not recommend it for your climate. You want your heated return fuel to mix with the bulk cooler fuel in the tank. Ideally you should have a spear to drop it back into the fuel so you create less vapours in your tank.

 

[desertrefugee]

Ugh. I hadn't thought about vaporization potential. Dang it. And yes, the low pressure supply side of the pump.

Thanks for the thought Tony.

 

[DaveKamp]

Yeah, Tony is 300% here... short-shunting not only means vapor introduction and high fuel temps, it tends to yield instable fuel pressure in operation. One wouldn't think that in a gasoline/venturi application that fuel temperature would have as great an impact as say... a diesel (where excess fuel is helping cool the injector tip AND helping warm fuel stock in extreme cold temps), but it helps stabilize the temperature of the injector pintle, which has a definite impact on it's response to PWM pulses.

 

[desertrefugee]

Exactly why I posed the question here. Live and learn. (The learn part is brazing brass to steel. I suck at it).

Thanks for the heads up, gentlemen. Probably saved me some unpleasant experiences on the road.

 

[Ansimp]

:good: :salute:

 

[DaveKamp]

The learn part is brazing brass to steel. I suck at it.

Yeah, well, that's about speed and control... and having plenty of like coupons to get the specific settings and technique down right BEFORE moving to the 'real' piece. If you're doing lots of fittings, cut plenty of test pieces, and run them... make your mistakes and get it down.

And don't feel bad about fouling up the practice coupons- that's what they're for... and don't think that 'experts' make it look easy because it is.

It isn't.

I'm not good at it... and I've brazed plenty of bicycle frames.

 

[Ansimp]

You could always just use solder with a neat fit if you don’t want to braze.