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ideal fuel pressure for webber or dellorto carbs

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pvergon

Senior Member
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hi there,

anyone out there knows what is the correct fuel pressure i should expect from a fuel pump to be able to feed two dellorto 40 DLHA carbs??? please let me know what electric fuel pump can work for these carbs and were you suggest is the best place to hide the pump considering that i need lots of preasure for the two heavy gas drinkers /ubbthreads/images/graemlins/eek.gif.

I do want to leave the original fuel pump, but do i have to cut the little arm that connects to the camshaft? or should i leave it? /ubbthreads/images/graemlins/confused.gif Will the work simultaniously? Common sense tells me that the original one will obstruct the new one, which makes me wonder what to do with the original one? please let me know what you would do.

i also want to buy a fuel pump that would work with the stromberg or SU (1.75 inch) carbs in case i ever want to save TONS of money on gas.

As always your advice is bienvenido - meaning more than welcome /ubbthreads/images/graemlins/thumbsup.gif.

thanks .... Paul
 
Re: ideal fuel pressure for webber or dellorto car

Hi Paul,
Fuel pressure should be no more than 3 - 4 psi. You do NOT need lots of pressure. On the Weber type carbs, as well as the SU's they will not stand high pressures, the float valves will not shut off. There are several low pressure electric pumps available. 15 gallons per hour pumping capacity should be more than adequate. The pumps are usually mounted near the fuel tank.

Webers will not require or use any more gas than SU's would. The fuel flow required is determined mostly by the engine displacement & rpm at which it is running. More carburetors usually means that each one flows less fuel.

It's not clear to me why you want to leave the mechanical fuel pump in place. The original operating pump, if connected in line (series) with the electric pump, will cause more fuel pressure (too much for sure) - with pumps connected in series (simultaneously), the pressures will add. If you cut the arm off & run the fuel line through this pump, the valves in the mechanical pump will restrict fuel flow. The best way is to use only the electric pump & put a block off plate in place of the mechanical pump, or I guess that you could just leave the mechanical pump in place & totally bypass it - look kind of strange though.

As I said earlier, SU & Weber/DellOrto carbs have similar fuel pressure requirements.
D
 
Re: ideal fuel pressure for webber or dellorto car

I run my Dellorto DLHA 40 at 1 1/2 pounds of pressure and it works great. I tried taking the regulator out of line and running at the pressure my mechanical pump delivers....bad mistake...gas everywhere. A case of Less is Better.
 
Re: ideal fuel pressure for webber or dellorto car

I agree with the above, running 40 DCOE on my Spitfire with stock pump, 1.75 inch SUs on TR4a with electric pump and bigger diameter gas line to get lots of volume with highly tuned engine but needed Holley pressure regulator to reduce the pressure.
It is more volume of gas you need, not higher pressure.
Simon.
 
Re: ideal fuel pressure for webber or dellorto car

The only thing I would add to the good advice given would be to check the setting of the regulator with a fuel pressure guage. Put a T in the fuel line to attach the guage. Check with the engine running.
 
Re: ideal fuel pressure for webber or dellorto car

I recall reading somewhere - possibly on this forum - that fuel pressure regulators (especially cheap ones) also severely restrict flow, so it is better to go with a pump that puts out the correct pressure and not a higher presure pump with a regulator.
 
Re: ideal fuel pressure for webber or dellorto car

Tony, I certainly agree with you.

The measure of fuel flow required in a gas engine is called brake specific fuel consumption (BSFC). This runs about .5 lb/horsepower/hour on the average engine.

At 150 hp & gas weighing 6 lb/gallon, this comes out to 75 lb per hour or 12.5 gallons per hour. The later SU electric pumps are rated at 15 gph & are the correct lower pressure.

The cheap Facet pump will do the job, but it is kind of noisy.
https://www.jcwhitney.com/autoparts/ProductDisplay/s-10101/p-1514/c-10101
It is rated at 2-4 psi & up to 30 gph. Much cheaper here than at Moss Motors or some of the other mainline suppliers. It has the added advantage of being able to connect either positive or negative ground.
D
 
Re: ideal fuel pressure for webber or dellorto car

hi people, i really appreciate your help. Dave, i wanted to leave the mecanical fuel pump to mantain a bit of originality, but, hey who am i kidding, the car didn´t bring any dellorto carbs in the first place.

i do have an electric fuel pump and will try to use it bypassing the mechanical one. i´ll let you know how things go. do you think the facet type will pump enough fuel even if i install it near the fuel tank? i´ll let you guys know how i do.

Mark i thank your advice, i already checked the presure with a gauge, and it didnt show any pressure at all, the hose between the carbs is super soft which tells me that very little fuel is passing by the fuel system.

paul.
 
Re: ideal fuel pressure for webber or dellorto car

[ QUOTE ]
Do you think the Facet type will pump enough fuel even if I install it near the fuel tank? I´ll let you guys know how I do.
Paul.

[/ QUOTE ]
As I said above, your engine shouldn't require more than about 12 gph fuel flow & the Facet pump is rated up to 30 gph. It should be fine. Since the pumps are better pushers than pullers, a location near the tank will help.
D
 
Re: ideal fuel pressure for webber or dellorto car

just to let you know that i installed the electric fuel pump and so far everything is fine although i haven´t been able to test the carbs on the street, i´m about too and i´ll let you know if the electric one brings enough fuel to the carbs.

what is the estimated miles per galon that two strombergs or SU carbs should do on a four cyl engine?

and how many should i expect from the dellorto or webber. do they consume a whole lot more gas then the SU type?
 
Re: ideal fuel pressure for webber or dellorto car

[ QUOTE ]

what is the estimated miles per galon that two strombergs or SU carbs should do on a four cyl engine?

and how many should i expect from the dellorto or webber. do they consume a whole lot more gas then the SU type?

[/ QUOTE ]
Hi Paul,
I have no idea what mpg you will get. It depends greatly upon how you drive the car. Likely, 18-28 mpg.

As I said earlier:
"Webers will not require or use any more gas than SU's would. The fuel flow required is determined mostly by the engine displacement & rpm at which it is running. More carburetors usually means that each one flows less fuel."
D
 
Re: ideal fuel pressure for webber or dellorto car

crystal clear, on the consuption data.

i know it depends mostly on the driving habits and this means that i will be in trouble then, cause here the speed limit signs only to decorate the road and hardly anybody respects them.

its a paradise for those who love the speed and nice curvy roads.

thanks for all your help dave, i do appreciate it much.

saludos /ubbthreads/images/graemlins/savewave.gif

paul.
 
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