Fuel regulation problem - is it that simple?

[korg_geek]

Hi guys, I picked up a 1973 240Z about six months back that i've been personally restoring back to a "tasteful" level. The previous owner was a wonderful japanese fellow who took marvelous care of the machine. The only problem i've had with it since its purchase is what i thought was a carb problem. It has dual 1971 SU's, installed to replace the faulty 73 carbs. They were "professionally tuned" a year ago, which is why i was surprised to notice bad fuel economy, dark, gas-smelling exhaust, some occasional sputters and other tell-tale signs of a rich mixture due to unsynched/misadjusted carbs. So i planned on getting it looked at - until the #1 Zcar pro in the area told me, flat out, that the problem wasn't with the carbs, but the fuel pump.

See, the pump was replaced a year ago with a new electric model (replacing an older model i'm assuming was also electric since this is a '73 and all had their pumps replaced). This guy told me, over the phone, without ever seeing my Z, that the pump is running at way too high of a PSI and i just need to slip in a regulator to adjust it down to 2.5. Okay, that sounds awful easy; and the only reason i'm skeptical is that i ALWAYS hear that this situation is a carb problem, not a fuel delivery problem. Does anyone know if lacking a fuel regulator causes a Z to run really rich? This guy's got 30 years of Z experience (from Nissan itself, no less), but I've always heard that regulators were neat add-ons, but not that important to daily performance... anyways, thanks a bunch for reading this! :classic:

[Cuong Nguyen]

Depending on how much fuel pressure the car has at the moment, the mechanic may be right.

SU carbs are designed to work with a low fuel pressure of around 2 to 4 psi (unlike EFI engines which require significantly higher fuel pressure for the injectors). Check out how much the new electric pump is putting through the fuel lines and take it from there to decide if you need a fuel regulator or not.

If you dont think its the fuel pump being to strong and it may be the carbies, then have the fuel to air ratio checked by a workshop with an exhaust gas analyser, this will tell you if the carbs are running too rich or lean.

Hope this help, good luck!

[2ManyZs]

The mechanic may be right. If I remember correctly, a fuel pressure regulator was part of the box of parts I received from the Nissan dealer for my 73 along with an electric fuel pump. It was part of the recall on the 73's to cure the vapor lock problem they had with the flat top carbs. Other parts were the fuel line heat shield and a 7 blade fan.

Try a pressure regulator, they are quite inexpensive. If that is not the problem then you can look into a carb synchro and mixture correction. Sounds like you have a mechanic that knows Z cars pretty well, you are one step up on a lot of people.

[korg_geek]

thanks for the great input, guys. i'll keep all this in mind when i install my new regulator. we'll see how things go....