weber 40's and fuel pumps

[steve k.]

I like to hear the fuel pump. Was part of my start up sequence.  I think i remember hearing the e30 pump also. Withe the throttle bodies, electromotive would turn it on to build the pressure and then stop it until the engine start. 

 

Steve K. 

[Stevenc22]

Terry Sayther used a facet fuel pump in my vehicle after installing the weber 40's. So far so good. JP's 1600 gt also has a Facet in it from Terry.

[AustrianVespaGuy]

Haven't seen this mentioned yet, but you can always run an electric pump in ADDITION to the mechanical pump (the mechanical pump will still allow flow through it).  I did this when I was running sidedrafts; I like the simplicity of the stock mechanical pump and mine was in fine shape, but summers at 6000ft elevation in Albuquerque with 10% ethanol in the fuel would periodically lead to the gas boiling and I'd get vapor lock on startups.  So I put in an electric pump in the trunk with a manual switch on the dash so that I could just flip it on whenever I wanted to be *sure* of a solid supply of fresh fuel.  Didn't use it very much, but wasn't expensive and was nice to have from time to time!

[2002Scoob]

I’ve got the in-line style pump in the trunk, you only hear it wine when the car is off. Once she’s running there’s way too much else between the carbs, valves, exhaust, etc to ever notice.


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[TobyB]

On 8/29/2018 at 12:42 PM, Lee said:

Here.

 

"suction device with pump"

 

https://www.realoem.com/bmw/enUS/showparts?id=1733-USA-07-1982-E21-BMW-320i&diagId=16_0007

 

 

Shit, you're right, Lee-

the late e21's do. 

I just went out and looked, and there it is.

 

t

[Chris_B]

Steve, it is more important that you don't push too much fuel into your carbs than anything else. Weber says ~3 PSI is required- likely this pressure is as needed to open the needle valve in the float bowl and supply fuel. The factory pump, according to anecdotal information I have seen and limited testing I have done, puts out 3-4 PSI. Volume is another, often ignored spec. I dunno how much volume the factory pump puts out, but I can tell you that it is sufficient to supply my dual 45 DCOE setup with 38mm chokes with plenty of fuel. In my experience, the factory mechanical pump easily meets the requirements of dual DCOE carbs on 02 motors, with a huge amount less complexity, and danger) than electric fuel pumps.

 

Has anyone on the group has had a situation where the factory mechanical pump was insufficient to supply dual sidedraft webers?

[Stevenc22]

Interesting after reading this little article by Top End Performance, i think ill switch from the Facet pump to the Carter pump

 

https://www.racetep.com/manufacturer/carbs-and-injection/weber/electric-fuel-pumps.html

[Pouya]

On 8/31/2018 at 5:21 AM, Stevenc22 said:

Interesting after reading this little article by Top End Performance, i think ill switch from the Facet pump to the Carter pump

 

https://www.racetep.com/manufacturer/carbs-and-injection/weber/electric-fuel-pumps.html

well after reading this, I ordered the inline carter pump P60430 from rockauto.com for $37 shipped. I hope its not gonna leave me stranded. https://www.rockauto.com/en/moreinfo.php?pk=296271&jsn=4

Edited September 2, 2018 by Pouya

[Stevenc22]

^ yeah after reading that i ordered the more powerful carter pump from top end.

[Chris_B]

What is important with weber carbs is keeping the fuel bowl(s) full. What Top End says about the mechanical pump's output varying with engine speed is certainly true: it puts out more fuel when you need it, at high RPMs. This notion of "pulsing" fuel being a problem with mechanical fuel pumps is nonsense.

[kbmb02]

On 8/31/2018 at 5:21 AM, Stevenc22 said:

https://www.racetep.com/manufacturer/carbs-and-injection/weber/electric-fuel-pumps.html

 

I have a fair amount of data points to suggest that article ought not be viewed as the gospel.... -KB

[TobyB]

Actually, I'll be more direct- it's mostly wrong for a 2002.  I stopped 2 or 3 sentences into ignition.  

 

A mechanical pump uses a spring to  supply fuel pressure.  So the pressure it delivers is consistent,

except when the diaphragm is being pushed back by the cam to 'refill' itself.  It makes big

SUCTION pulses, but pressure simply drops, then comes back up.

That CAN cause seat wear of the float valve needle- which is why you see the rubber- tipped valve...

 

I tried to get that Carter to work with DCOE's and 38/38 and 32/36- every time I used it I needed a regulator.

 

And just about any pump CAN work- I use the Holley Red they say is so terrible.  The bypass regulator (Mallory,

in my case) works just fine- has for 15 years or so...

 

ymmv, of course.

 

t

[Son of Marty]

Actually i'll be even more direct- it's mostly wrong for Weber carbs in general. Pump pulses are of little to no concern to fuel level as once the fuel is passed the needle valve it just sits in the float bowl with no pressure on it, I think many people tend to look at the needle valve as ether open or closed but in fact the floats and the size of the needle valve should control the flow of fuel flow but under almost all conditions not all the way open or closed completely Weber has aided this by using a much longer tapper to the valve than a lot of other carbs, the dcoe's for 02's usually come with 225 needle valves and this is too large IMHO and leads to a veritable fuel bowl level a stock 02 will run better with a 175 needle and a club rebuild (292-302 cam 9.5 pistons ect) try a 200 needle and for racing a 225-250 will be plenty. That brings up fuel volume  a stock 2002 that has a set of Webers should not when properly jetted use more fuel than it did with a single barrel Solex plus the added airflow gained from a very small gain from having 1 throat per cylinder, after all the only way to increase hp is to increase volumetric efficiency, until you pass more air you'll not use more fuel regardless of how many carb's your running.    

[Chris_B]

When you think about it, the mechanical fuel pump is "pulsing" pretty darn quickly. The camshaft turns at half the rate of the crankshaft, so at say 2000 RPMs, the camshaft obviously is turning at 1000 RPMs. That means that the fuel pump is pumping 1000 times per minute, or roughly 17 time per second. I don't know that much about fluid dynamics, but I would guess that pumping at this rate would seem more like a vibration in its action on the fuel than some kind of sucking and pushing action that would affect the carb.

[TobyB]

...except that it only draws as much fuel as has been used in the cam rotation.  So at low flow,

it sits on the spring for 355 degrees of cam rotation, then draws fuel in the last 5 degrees.

At high flow, it may come off the spring and be lifted by the cam for 90 degrees- maybe.  

So it's pretty consistent pressure- with interruptions.

 

And it's been around for a looooooong time...

 

t