Fuel Pressure regulator for Airtex 8012S electric pump

[jalexquijano]

My 1972 240z has an airtex 8012s electric fuel pump which pushes 5 to psi at 30gph. I read that SU Carbs dont like more than 4.3 psi is this true? Which fuel pressure regulator is recomendable? Holley?? WHenever the car sits at idle on traffic the plugs start to get black. I need to regulate the psi.

 

Please advise.

[datzenmike]

Get this fixed yet??? http://community.ratsun.net/topic/68156-rough-idle-rpm-drop-and-stalling-at-intersections/

[dgi]

The correct spevcified fuel pressure for SU carbs is 3.4140 psi.  

 

See http://elfecc.no-ip.info/510/SU_Carbs/SU_Carbs.htm for more details and tuning instructions.  This manual is more specific to the 510 carbs, but is applicable to the Z carbs.

 

Personally, I have my Z's carbs limited to 3.5 psi by my electric fuel pump's internal regulator and proven by an inline gauge. My exhaust manifold is not insulated, my fuel lines are not insulated, and I do not have a return fuel line (it is blocked off),  No idling issues at all.

 

I've read your other thread that Mike asked about.

 

You mention a stumble coming off idle.  Generally, this is caused by too light or no oil in the oil reservoir.  What? Oil in carb?   You are kidding!   No, read the section about the Venturi Control System in the manual linked above.  Too light and you get the stumble.  Too heavy and the idle doesn't fall back down as it should.

 

Also pay attention to how the idle adjusting knobs should be set and I quote, 

 

Tighten front and rear idle adjusting nuts all the way, and turn out as required according to outside temperatures and altitude. Note: Always turn in or out these nuts equally.

 

 

[DanielC]

I am not lucky enough to own a 240Z.  But I have several 521 trucks, and have had then since the 1970's. 

In my experience, a reliable trouble free Datsun is a stock one.  Very few people have the engineering knowledge Nissan had, and still has.  

Put a stock Nissan 240 Z fuel pump on your Z.  Especially with stock SU carbs.  I could be wrong, but I think the stock 240 Z fuel pump is mechanical.

 

Most people think the running engine forces amechanical fuel pump to pump fuel.  This is not how a mechanical fuel pump works.  The running engine moves a diaphragm against a spring, and it is the spring that supplies fuel pressure.  The area of the diaphragm, and the spring are counterbalanced by the pressure the carb float puts on the fuel inlet needle.  Additionally, a mechanical fuel pump increases flow, as engine RPM rises.  Just what the engine needs.   An electric fuel pump knows nothing of how the engine is running, so by default it has to always try to supply more than enough fuel to run the engine at 7,000 RPM, WOT.  Even at idle. 

[jalexquijano]

Well, i have no mechanical pump as when i purchased the car it came with the block off plate where the mechanical pump was located. Besides, i have read that electric pumps eliminated any vapor lock. THe problems i need to tackle are the following:

 

1. Slight hesitation (back and forth shaking) after releasing the clutch and accelerating from 1,000 to 2,000 rpms. After 2,000 rpms the hesitation is gone. This is also present whenever you drive through a broken road.  I already changed the differential mount thinking it could be worn. The problem is still there. I am using ATF as damper oil!! Should i switch to 3 in 1 motor oil?? (Blue label)

 

2. THe car has an Airtex 8012s electric fuel pump installed which advertises as 5 to 9 psi. Measured the pressure at the rear carb and it shows 5 psi. However no overflooding off the float bowls.

 

3. After driving the car around and stopping at several intersections and traffic lights. Got home and plugs were fouled.

 

SHould i just purchased a Holley Fuel Pressure 12-804 regulator to lower the psi to 4? or should i purchase a Mallory 4070 LP which is advertised as 4 psi and hence no need of regulator.