Fuel Pump and fuel flow

[gt_james]

I just spoke to some more knowledgeable chaps than myself and I was told that you cannot make a holley 12-803BP into a 1-4psi reg with the 12-804 spring, they're not compatible. But the 12-803BP although advertised as 4.5-9psi will regulate down to 4psi. Also a weber IDA with a #300 needle will tolerate 4.5psi, so you can use the 12-803BP reg with an early S1 or 2 nikki and webers, but for an S3 nikki I think you'll just be out of range with this reg, so you'd need to spend more, either the KSE reg, or aeromotive 13301, or go with a louder and more restrictive non bypass 12-804.

[rustyrescue]

thank you, very thorough....I am more used to Lucas PI on my old Brit!
I think I will seek a Carter pump in the new year, not sure which filtering. I assume the stock pre pump filter will restrict too much.
Regarding regulator, I am unsure which Nikki I have on it currently.....I bought it off a car.
Our car is S2, the carb currently on it looks like the one I took off....can I check?

[gt_james]

Sorry not that sure, this should help. http://www.wright-here.net/files/manual ... 9-1985.pdf

[rustyrescue]

perfect thanks its gonna be right for spring!!
If I use the holley BP regulator it is new to me. Stock the return flow is off the carb. do I leave than connected and Tee in with a one way valve to prevent flow back to the carb the regulator? or do I really need a return type regulator seeing as the car has a return off the carb as you say? This will mean the pump is never operating against a blocked/stopped line or over pressuring the needle valves.

[gt_james]

You can run a non bypass (deadhead) reg and you then wont use the return line on the car, and the return outlet on the carb will be capped off. As you say, this means the pump is operating against a blockage when the regulator closes, makes more noise, more stress on the pump, hotter fuel. Your needle valve will only ever see the pressure that the regulator is set to, but the pump is at full pressure all the time.

A bypass reg (BP) goes after the carb on the return line. So from the supply fuel hard line on the car a hose goes straight into the carb like stock. Or add a 10 micron metal case filter if you like. There's no restriction of the regulator to fuel flow to the carburetor. Then the return from the carb goes to one side of the 12-803BP regulator, the other side has the gauge, and the bottom port goes to the return line, and back to the tank.

also a note on other carbs for posterity:
If you're using a carb like a weber IDA that doesn't come set up for a return, you would use a T piece, or use the top port where you access the mesh screen as the supply, and the port where the banjo goes as the return port, but this is less common, and I think you'd have to remove the mesh screen.
If you want to be really trick you can drill the area with the mesh to 4.5 to 5mm for less restriction to the needle, which helps as the float bowl is small on an IDA and we need to be able to fill it quickly, so the biggest needle valve you can get, and opening up the restriction at the banjo inlet helps.

[rustyrescue]

thank you, you are a mine of information....we run a weber on my wifes Stag straight off the standard pump with no return and it seems fine currently!
I asked a supplier regarding the malpassi filterkings and was advised the V8 black version has been tested as "moderate" pressure to 350 loitres per hour and the smaller one to about 300 lph.
So for a non return version it would seem they may be up to the job as well.
I will ponder for a bit! It seems a Carter with a Filterking on a closed circuit or a Holley BP on an open circuit, with the BP reg simply mounted on the bulkhead between the carb and the hard return line.
I assume also the Bypass type regulator works in effect the other way round.....the before carb regulating pressure out by restriction, the after carb version regulating pressure in to it by altering the flow out.

[rustyrescue]

A Carter pump has been ordered, do others normally mount this pump which is quite large in a similar area to the original plate/pump/filter assembly?
I think I will initially try a closed circuit with the big (V8) Malpassi filter/regulator in one unit in the engine bay.
I just need to source a sensible pre pump filter and bracket to replace the tiddly original paper one.

[gt_james]

Yeah try and mount it in a similar area, and use rubber mounts. Ideally rubber mount a plate to the body, then rubber mount the pump to the plate. You might be able to hack the stock plate around to fit, when I did my holley pump I started from scratch though.

[rustyrescue]

Carter pump obtained, its biggish ...see other post.
I have a regulator on the bulkhead now, using the current pump and I continue to get occasional flooding, Reduced from 4.5psi to 3.5psi pressure, the rear float level is too high ...over window, despite setting the float levels. Looks like I need to pull top off carb again.
I remain unsure if the carb I have on the car now is from the same year, I think all I can do is cross reference the various jet sizes. The carb looks the same, exactly.
I may look at the floats/ needle valves in the various 3 carbs I have!