Lotus Elan

Fuel pump advice

PostPost by: robb4100 » Mon Feb 18, 2008 3:42 pm

I am in the process of switching to a negative earth system and am replacing an electronic fuel pump. the one that I currently have is a facetted type and in doing some research into low pressure fuel pumps came accross this.

Fuel Pumps and Fuel Pressure:
Fuel delivery is critical to the proper performance of any Weber carb. From a basic 32/36 DGEV to a set of Triple Sidedraft DCOE's. Webers rely on a stable full float bowl in order to mix the fuel and air correctly. Mechanical pumps very rarely do this. They pulse fuel instead of giving a smooth even delivery and the amount of fuel varies with engine RPM.

A Proper Electric Fuel pump will give the best performance and most stable tuning for any Weber carb application. We use only High Volme and Low Pressure pumps. Webers work best at approx 4 psi of fuel pressure (Not 2 psi like many of the older books stated.) and you need Volume not Pressure to keep the float bowl full.

We ONLY use the Carter Rotary pumps. They are High Volume (60-70 GPH) but only 4 psi. This is PERFECT for all Weber applications from a Single 32/36 DGV on a Truck, Jeep or Car to a Triple Sidedraft setup on a Road Race car making 300 HP...This pump DOES NOT and SHOULD NOT use a Pressure Regulator for any reason. That is why we use it....



from this website http://www.racetep.com/webfuelspark.html#webfuel


Does this sound like good advice? They also strongly recomended against the facetted fuel pump.

Thanks

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PostPost by: CBUEB1771 » Mon Feb 18, 2008 4:30 pm

Robb,
This quote reads like someone has a huge overstock of Carter fuel pumps to unload. The fuel level in the float chamber is an important parameter and it is influenced by many factors. The flow capacity of the pump is not a factor unless it is so low that it can't keep up with demand and the float chamber empties. I have Webers and a mechanical fuel pump in my +2S. At 75 mph on a highway I probably use something between 2.5 and 3.0 gallons per hour. The Carter flow rating sounds like overkill at nearly 25 times that consumption. The Carter discharge pressure also sounds high. The pressure stated in the Lotus service manual is something like 1.25 or 1.50 psi. You haven't indicated how you plan to use the Elan. For normal road use there is nothing wrong with the standard mechanical pump or the small Facet. You won't need much more capacity unless you are racing. Today's replacement mechanical pumps have too high a discharge pressure and you will need an adjustable regulator. I chuckle at the notion that a rotary fuel pump produces a more constant level in the float chamber. In operation the interaction of the float and the needle valve cause the fuel level to vary regardless of the type of pump. In the real world we also have cornering, braking and engine loads that push the fuel around, not to mention the occasional pothole in the road.
Last edited by CBUEB1771 on Mon Feb 18, 2008 5:37 pm, edited 1 time in total.
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PostPost by: iain.hamlton » Mon Feb 18, 2008 4:59 pm

A Pressure regulator is not a bad idea
best regards, iain
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PostPost by: frearther » Mon Feb 18, 2008 5:48 pm

I use a Facet pump and a regulator in my street-tuned S2, and evberything seems to be fine. I have pressure set at 1.5 psi.
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PostPost by: batfish » Mon Feb 18, 2008 7:53 pm

I have also seen this artical and so at the recent Autosport Racing Car show asked Webcon about which pump to use for racing with 45DCOEs. They said they had never had a problem with the Facet pumps and infact that is what they sell along with the Weber carbs

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PostPost by: RotoFlexible » Mon Feb 18, 2008 9:11 pm

Robb,

I read the same Carter propaganda and, like others here, thought it was a bit over the top. Nonetheless I bought one, a 6 psi model I think. Don't yet know if it will work w/o a regulator as I don't have the car to the point where I can drive it. I was a little concerned with the some of the reliability issues I'd read about in connection with the Facet, but I suspect they are largely groundless, and the 1.5 psi model is certainly a nice fit (both size- and pressure-wise) for the car. I'll report on the Carter when I'm able to drive the car - sometime in March I hope! If you decide on a Carter, Summit Racing is a good source.
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PostPost by: CBUEB1771 » Mon Feb 18, 2008 9:47 pm

RotoFlexible wrote:Don't yet know if it will work w/o a regulator as I don't have the car to the point where I can drive it.


Finding out that you need a pressure regulator can be a heart-stopping experience. If the inlet pressure is too high then the float will never develop enough buoyant force to close the needle valve. This results in the float chamber filling and fuel being pumped out through every jet and vent in the carburettor with a significant probability of fire. It is not safe to determine this by starting up and driving off. You should test this on the bench (in a safe place) with the pump and one carburettor outside of your Elan. If the needle valve closes and the fuel flow stops you may be OK. I am quite certain you will need to regulate down to less than 2.0 psi.
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PostPost by: twincamman » Tue Feb 19, 2008 5:01 am

I have replaced all my cars pumps to electric --[ a 998 sprite -a renault europa and 2 twincams a 7 and an elan ]--no pressure regulators involved -----just turn the key and let the needle and seat do the job -----quicker starts and I have never experienced fade at top end with webbers or su s ----ed
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PostPost by: frearther » Tue Feb 19, 2008 12:02 pm

OTOH, I experienced Russ's problem when I didn't have a regulator installed, even with the Facet at its lowest setting. He's exactly right - it's a heart-stopping experience.
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PostPost by: RotoFlexible » Tue Feb 19, 2008 12:45 pm

CBUEB1771 wrote:Finding out that you need a pressure regulator can be a heart-stopping experience.


Thanks for the cautionary note, Russ. The regulator goes back in this evening, before I have a chance to prove you right. The car was certainly sensitive to pressure with the previous electric fuel pumps, although no disaster ensued.
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PostPost by: robb4100 » Wed Feb 20, 2008 12:11 am

I always get good advice from this site- Thanks

A facetted pump (1.5- 3 psi) is on the way along with a regulator to adjust the pressure down to 2 psi. Was able to get both from Dave Bean

Thanks so much everyone.

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