Carburettor fuel pressure question.

[haison]

I've converted 5ME EFI to carby using a 4MU carb.
This particular model of carby has a fuel return line.
Due to time restraints and the inability to find a 4M fuel pump that works I'm wondering if it's possible to use the EFI pump to fuel the carb.
I know under normal circumstances the EFI pump pressure would be too high but with the return line I'm hoping the excess fuel will go straight back to the tank.
Am I right or should I just go with the mechanical pump?

If I have to go with the mechanical pump can I use the charcoal canister to fuel it or do I have to drop the tank and take the pump out?

This is in a 84 Supra.

Thanks!!!

[SillyCarS]

its like 6psi or something

[haison]

The mechanical or EFI pump?

[SillyCarS]

on th rg i used an electric push style pump, it ran at about 6psi

running efi will prob not work as even though there is a fuel return it will flood the venturies as the system has friction in the lines

[haison]

I figured as much. Someone is trying to convice me it'd work.. Something about there being a needle that'll cut off flow when the carby is full.

[mrshin]

I've converted 5ME EFI to carby using a 4MU carb.

Brilliant.


...why?

[haison]

Apparently better fuel efficiency and more power.

Real reason i did it?

Have you seen the amount of vacuum hosing n crap I'd have to figure out how to put back??
I had to get it moving again cause I'm moving house soon and it'd be a few months before I finish hoarding 7M bits and upgrade the suspension n brakes etc.

[haison]

Oh and the original EFI gear was ripped off in a fit of excitement along with the engine thinking I'd rid myself of the 5M for good.

[Screamn_Sleeka]

EFI pump will be too high psi and over flow the float level, thats why you cant use them. Doesnt matter if there is a return line or not, pressure is pressure.
6psi like the other guys said sounds about right, but i wouldnt use anything about 6.

[oldcorollas]

you can get really cheap solid state type pumps that can only do about 3psi...
like fuelmiser brand or some such....

no need for the return line from the carb.

[Screamn_Sleeka]

The return line is so the fuel circulates and stays cool, to stop it from boiling in the carby, id keep it.

[The Real Roadrunner]

if you keep the efi pump in the tank use a t piece in the bay
one side from efi pump then the run back to the tank and on the side into the carb and you may not need a low pres pump and it shouldn't blow the needle open
this is bodge as but if you just need to move it then it could help
other than that you really should get the proper pump run a low pressure reg and a return line.
give it a go if you dont want to spend money on a part you wont use later

[oldcorollas]

The return line is so the fuel circulates and stays cool, to stop it from boiling in the carby, id keep it.

are you sure?

the return line usually comes from the top of the fuel inlet.. ie, above the float needle and seat.

having the retun line shouldn't have any effect on the fuel that is already sitting in the fuel bowl...

or am i missing something?

[oldeskewltoy]

Weber makes a adjustable FPR that goes from 85psi down to as little as 1.5PSI. You can get it through Alamo Motorsports* in the US. Here is the listing showing the FPR that Weber has......
http://69.0.202.131/html/fuel_air_fi...regulators.htm

* - [email protected]

[haison]

The idea was to grind the tip off the return nozzle which will allow more return flow.
Screaming_sleeka is right in saying pressure is pressure.
Methinks i'm gunna tell this dude to go shove something uncomfortable in an uncomfortable place and go buy a fuelmiser pump.. they're on special at autobahn atm
Thanks for your help guys!!
+rep to all