weber fuel rates?

teenerted1 · 10-17-2007, 01:39 PM

what fuel delivery rate should i be looking for?

have a 1970 911 with a 1978 SC 3.0L engine and running Weber 40's

i might have a fuel delivery issue but cant find anywhere that states the correct rate i should be running.

help

Brent Lineker · Brent Lineker's Garage

Not sure if it helps but I run 3.5lbs of pressure,not sure by what you mean by fuel rates?I have the 2.7 with 40ida's with ssi's and early style exhaust.

911pcars · 10-17-2007, 02:08 PM

If it's the fuel pump volume, I believe Steve Weiner and others suggest min. 1 liter/min. should be sufficient.

Sherwood

Superman · 10-17-2007, 02:33 PM

That's the Rule of Thumb. Ever since Fred Flintstone got a self-powered car for Wilma, the test has been to disconnect the hose at the carb (and the coil wire) and, while someone runs the starter, hold the hose in a pop bottle. If it fills the pop bottle fairly quickly (like in a half-minute or so), then there is enough volume.

teenerted1 · 10-17-2007, 02:47 PM

Quote:

Originally Posted by Superman

That's the Rule of Thumb. Ever since Fred Flintstone got a self-powered car for Wilma, the test has been to disconnect the hose at the carb (and the coil wire) and, while someone runs the starter, hold the hose in a pop bottle. If it fills the pop bottle fairly quickly (like in a half-minute or so), then there is enough volume.

so is that one pop bottle per side? or should i do that right after the filter, before it splits.

911pcars · 10-17-2007, 04:05 PM

Quote:

Originally Posted by teenerted1

so is that one pop bottle per side? or should i do that right after the filter, before it splits.

That's the min. spec for one fuel pump, no matter how many holes in the delivery end. Thus, measure before the split.

Sherwood

Eagledriver · 10-17-2007, 05:53 PM

1 litre per min seems a little low to me. I don't have the numbers infront of me but I think the MFI pump on my 72 pumps about 1 quart per 30 sec.

A 200 HP engine burns about 15 GPH. The general rule is to have at least 50 percent more capacity than the engine requires. This would be about 22-25 GPH or just under 2 quarts per min.

-Andy

Zeke · 06:02 PM

Quote:

Originally Posted by Eagledriver

1 litre per min seems a little low to me. I don't have the numbers infront of me but I think the MFI pump on my 72 pumps about 1 quart per 30 sec.

A 200 HP engine burns about 15 GPH. The general rule is to have at least 50 percent more capacity than the engine requires. This would be about 22-25 GPH or just under 2 quarts per min.

-Andy

Yes, but your MFI pump is pumping at a much higher pressure in order for the MFI distribution pump to function. There is no correlation between the 2 systems, AFAIK. Pumping freely into a jar seems like a jackleg way of evaluation.

Yes, I know that's the way things are measure and calibrated many times, but put something under a load and you might find a different factor. Hence, the use of a fuel pressure gauge AND flow.

RoninLB · 10-18-2007, 10:15 PM

another quick check of condition is motor amp draw. And factory max flow is without load. Otherwise I'm already plumed for a FP dash gauge.

also.. I've read in hard text that 75k miles is expected good life of the Bosch FP. Over 100k is one forot in the grave and the other on a banana peel.

teenerted1 · 10-19-2007, 08:05 AM

Quote:

Originally Posted by RoninLB

another quick check of condition is motor amp draw. And factory max flow is without load. Otherwise I'm already plumed for a FP dash gauge.

what is the correct motor amp draw?

Eagledriver · 10-19-2007, 08:18 PM

Quote:

Originally Posted by milt

Yes, but your MFI pump is pumping at a much higher pressure in order for the MFI distribution pump to function. There is no correlation between the 2 systems, AFAIK. Pumping freely into a jar seems like a jackleg way of evaluation.

Yes, I know that's the way things are measure and calibrated many times, but put something under a load and you might find a different factor. Hence, the use of a fuel pressure gauge AND flow.

My MFI pump is running my carbs at very low pressure. I believe that is also the application in question. You are correct that the pump will flow less at MFI pressure but what actually happens with the MFI is that the pressure drops as the demand increases.

I guess my main point is that for a carbed 200HP car the measurement I gave will give enough fuel. If you were running MFI then the MFI pump would give enough also since it's the same pump on the Carrera RS. It might not flow enough at higher pressures but it wasn't designed for that anyway.

-Andy

RoninLB · 10-20-2007, 10:52 AM

Quote:

Originally Posted by teenerted1

what is the correct motor amp draw?

hi Ted

i couldn't find hard info on the normal amp draw. I believe it's about 4 amps.

On such a situation without such info I would test and look for a 10 amp red flag as an educated guess to a FP motor problem. Early_S_Man / Warren posted his educated position on

Pending fuel pump doom...

teenerted1 · 10-20-2007, 12:09 PM

well it definatly is the pump @125cc in 30sec

what is wierd is the one under there is simular to the one the teener had.

seems someone might have put on a prefilter too?

Jeff Higgins · 10-20-2007, 12:53 PM

Check the filter between the tank and the pump; I'll bet it's clogged. Way cheaper than a pump. If it's clear, check the screen in the tank, which is also way cheaper than a pump. Don't assume it's the pump just because you get poor flow at the carbs.

teenerted1 · 10-20-2007, 02:49 PM

Quote:

Originally Posted by teenerted1

well theres your problem.

thanks scott for calling when you did

and jeff you were exactly right. that filter of the tank before the pump was the culpret.
barely flowed below
above 400ml in 10seconds!!!!!!!

off to the parts store tonight or tomorrow for a filter or two.

teenerted1 · 10-20-2007, 02:50 PM

Quote:

Originally Posted by teenerted1

well theres your problem.

thanks scott for calling when you did

and jeff you were exactly right. that filter off the tank before the pump was the culpret.
barely flowed below
above 400ml in 10seconds!!!!!!!

off to the parts store tonight or tomorrow for a filter or two.

Jeff Higgins · 10-20-2007, 04:33 PM

I'm glad it was something cheap and easy. However, since Scooter was chasing jetting in an effort to fix what was really a supply problem, don't be surprised if it runs quite rich now that it is getting enough fuel. The sooty plugs you pulled last Saturday were probably representative of the true jetting. In other words, they were in the cylinders that were the last to be starved as the floats drained. The nice gray ones were undoubtedly only that way because those cylinders were running out of gas first, leaning just their mixtures.

RoninLB · 10-24-2007, 08:15 PM

Quote:

Originally Posted by teenerted1

what is the correct motor amp draw?

this is all i have.. i assume lower Bosch FP operation would lead to lower amp draw.

http://www.auto-solve.com/mech_inj.htm#MFI03

"The normal operating pressure within this system is approximately 5 bar (75 psi) and at this pressure the current draw on the pump is 5 to 8 amps. "