Fuel pressure with twin 45 Webers BMW 2002 1972

[chiz 3]

Looking for some help with fuel pressure reduction.Have a in tank fuel pump- Bosch 0 580 453 019- I think a pretty common set up for E30's ? Puts out 3 bar or 43.5 psi way over the top for carbs which need 3-4 psi max. Had a holley fuel pressure reducer with gauge, can't set it reliably to stay at 4 ish, constantly changes and causes carb overflow. Can't seem to find any in tank Bosch with way lower pressure and tank has no other fuel exit underneath to put an inline pump like a Carter, low pressure high flow. Any ideas ? I suppose I could just have a foot filter and pipe in the in tank fitting and the use an in line pump ??

[*Glenn* 854]

Talk to Petroject (09) 4481071

[polley 916]

Pressure reduction is sub optimal because it usually results in flow constraints, what you really need is a high flow, low pressure pump. these are available from Dellorto and Weber specialists.

Alternatively you could hook one out of a motorbike e.g. Ducati - you may need two to get the flow

Or you could just get a carter pump off the shelf from any speed shop. Run a in tank low pressure lift pump (like the early e30's etc) into surge tank and feed the carter from the surge tank. Edited June 15, 2016 by polley

[chiz 3]

Thanks, Yes I do understand about the restriction of flow and the ideal Carter like pumps but I have an in tank pump [ with XS pressure] with associate fittings, I really don't want to double up with 2 pumps , surge tank and wiring-every extra bit to increase complexity and to go wrong. I was hoping someone would come up with an in tank low pressure high volume pump I could replace it with. Anyone tried a voltage reducer 12v to 6v to reduce pressure in an over enthusiastic but good quality pump ?? Or a simple in tank but from the top pick-up which I could attach a Carter to. I don't wish to start new exits underneath if I can help it.

[Neal 512]

I'd be inclined to do a carter which is well proven in Webber comp car circles (no need for fuel pressure reg)

I sold mine , but did have one for a 45 set up on my mini.

Mod your in tank fuel pump in a similar manner to this. https://youtu.be/8-Q4nDf_Bn4

[chiz 3]

Thanks both Neal and Ron , two valuable suggestions, from different directions.

[Neal 512]

Ron always has good points and does offer a tidy solution

I didn't pass on some learnings I'd pick with running 45s

dual 45s the key here hence something like a po4070.

45mm like to be filled fast at low pressure. Get minor or spikey fluctuations once full and the Webber float sticks and the fuel gets dumped via the primaries.

Sometimes hitting the 45 float area with a rubber hammer will restore the fuel shut off to the bowl or jumping back on the gas and off. neither is that practical when racing. Not something to find out at the end of a long straight wondering why the power hasn't backed off.

If going for an intank carb fuel pump do the research on flow rate and psi and if the car has a similar power output to your engine, also check if that vehicle has an external regulator to control pressure to determine .

Thought about running a fuel cell with bottom outlets ?