9 replies to this topic

[lotusk]

Hi all,

Can anyone please tell me roughly what fuel pressure I should be sending to twin HS4's? I'm running a facet pump with regulator. Engine is a 1380 with stage 3 head.

Appreciate this will be dependant on needles so just need a rough figure to get it through MOT and run the engine in.

Many thanks,

kieran

[GraemeC]

Around 4psi

[dklawson]

At 4 PSI keep your eye on the float bowls. These are still SUs and they will be happier a little lower at 2-3 PSI. If you see any overflow, back the pressure off a bit.

[GraemeC]

Sorry - I posted in haste!! As doug rightly pointed out, 4psi is the most you would want to see the pressure at, anymore is too much.

[Pooky]

Can excess fuel pressure cause excess fuel consumption? Is this going to be an obvious answer?

I'm using THIS.. Facet pump, as it suggested to use for 'fast road' twin HS2's (which is what I've got) but my fuel consumption is ridiculous, you can almost see the needle going down afaik there are no leaks...

Will an adjustable pressure regulator help?

Edited by Pooky, 18 July 2009 - 12:07 PM.

[Jordie]

Pooky is your car setup properly? carb fueling and timing?

When i fitted twin HS4's to my mini, it drank fuel. Like no tomorrow.

I swapped back to a HIF44 carb and got the same performance/driving and loads better fuel economy

[Ethel]

Fuel pumps have to overcome restrictions in the fuel line and acceleration forcing the fuel back towards the tank. The float valve is closed by the weight of the fuel displaced by the float (less the weight of the float), as the volume of the float is fixed there's limited scope for adjustment. If nothing was adjusted then higher line pressure would force more fuel past the valve until more of the float was submerged which would make the mixture richer.

Running a higher pressure pump and putting a pressure reducer (regulator) as close as possible to the carb is a good idea, even a fuel filter might do enough if that pump is set at just 5psi.

[Pooky]

Pooky is your car setup properly? carb fueling and timing?

As far as I can do it by myself, I balanced the carbs with a Carbalancer and used a Colourtune and set it at the light blue spark about 800 miles ago (it's a new engine).

RE timing, I'm on Megajolt and have only 'tweaked' a map I downloaded based on a stage 1 998 (I'm running 1061cc with 12G940 head, Morspeed PH3 cam and the twin HS2's) but the car runs quite well. Cam is timed in according to manufacturer.

Ethel, I've got a pretty chrome filter but have been considering a Filter King (Clicky) fitted, as you say, near the carb. Any idea if this will help and what size pressure to get? with my pump?

Cheers

Joe

[bmcecosse]

Just use the standard mechanical pump - it works - no need for regulators etc!
Fuel economy can be excellent on twin HS4s - you just need to set the thing up correctly. It will go far better on a properly designed inlet manifold - with no balance pipe - as used for a Weber, rather than the ghastly standard manifold, even when opened out to suit the larger carbs. The balance pipe creates havoc with the air flow. Single HIF 44 is easier to set up - and performs just as well - indeed - could argue it will be BETTER!

[Pooky]

Just use the standard mechanical pump - it works

Mine wouldn't. Well it did on my standard 998, changed the block and cam and it then it didn't! Seemed like the spacer block was the wrong size. Was easier to switch to an electric pump.