voslachlan

Hi all, Have managed to get the fuel system working with a reasonable degree of effort, now getting a stable 2.5-3psi to the carbs. A little while ago I rebuilt our SU HIF6 carbs with a seals and gaskets kit, however we hadn't actually run them long term until very recently. When we get it running in the yellow chassis, we noticed an intermittent fuel leak through the overflow even with the pressure set correctly, so I got some new float needles and seats which seemed to fix the problem. Now with a cooling system in place we've gotten it running and up to temperature, however still fighting some idle and mixture issues. At idle it sounds a little rough (could be due to an exhaust leak at the header flange) but certainly far smoother than it ever has. However, it still has very minor stumbles and backfires every few seconds (issue #1). It was also idling very high which we only noticed once every other factor was sorted, and even with the idle screw turned all the way down and the throttle shaft touching the carb body it still sits at 1.5-2k. Obviously a vacuum leak of some sort, but the odd thing is that when I block the float overflows with my hand, the revs drop severely and the engine dies off (issues #2). Which seems to suggest suction through these overflows, but I'm not sure how that would be possible - I would expect positive pressure if anything. The only way I can see manifold vacuum getting into the float is through the jet, but surely with the floats set at the correct height there wouldn't be any way for air to get in? Would appreciate some guidance or suggestions from the SU experts before I start swapping out parts and spending money on what is ultimately an intermediate step before the RB path. Cheers, Lachlan

Cheers for that link, very helpful. Seems like the pressure regulator in our setup slightly complicated things compared to that more standard setup, but likely still lots of similarities. Currently have the alternator unplugged due to a missing voltage regulator so will check if the behaviour matches that post when it’s all connected up.

Update that’s hopefully helpful for people with a similar fuel setup in their S30’s: I pulled apart the Nikki pressure reg, and the mechanism instead seems to be pretty standard affair, with a sprung piston with a rubber insert on the tip acting as a diaphragm over an orifice on the inlet. However, the 12V in goes to a coil/electromagnet that when powered, pulls the piston up - effectively bypassing the spring so it will always flow fuel through the regulator. My guess is this is for safety, to keep fuel at the rear of the car in case it gets in an accident with ignition still on for example, since currently the fuel pump runs as soon as the ignition is on. However, this is a guess and I’ve still got some experimenting to do to figure out when the pressure reg 12V is switched on.

Hi all, Our '76 260z 2+2 donor car came with an electric pump (Goss GE002 - very little info out there and likely not standard) and a powered fuel pressure regulator (Nikki SB-10, seems to match with other photos on the web but can't find any documentation about it) with both in a hanger behind the driver's side rear wheel arch. We've been trying to get it reliably pumping fuel with the exisiting setup (didn't work at first, replaced pump but issue was blocked connector, now back to previous pump) but are at a standstill. When the fuel hanger is sitting on the ground, fuel reaches the mechanical pump at the pump with no issues, whether the fuel pressure reg is plugged in or not. When the hanger is lifted up into position, fuel comes through only with the pressure reg unplugged. And with a filter inline as per standard, it will only work if the hanger is low, it's almost like the pump can't draw through the filter unless there is a siphoning effect out of the tank. Since we are just trying to get it on the road for now and have plans for EFI down the road, can anyone provide info on the mystery pressure reg and how it's supposed to work? Why does it need power? Is it safe for the SU carbs to run the Goss fuel pump with no regulation directly into the mechanical pump and into the carbs? Why an electric fuel pump by the tank in the first place? Have attached a photo of the hanger as removed from the car (just with replaced connectors) Cheers, Lachlan

Hey all! I’m the previously mentioned son, thought I’d chip in on the discussion. The carbs we got were taken off a 260z, and I believe they replaced the stock flat tops as an upgrade, so I’m not sure what year the carbs originally came off. They seem to be 3 screw Datsun (ie. non British) round tops with no tab on the inlet flange, I have attached photos for reference. Hopefully less effort to get running? They were taken off a running car and left in a box since then. Also are we missing the float chambers? The flat tops did not seem to be working properly, although with our limited experience we can’t really say if it’s the fuel pump or carbs that are the issue. When fed from a funnel, fuel passed through the pump even before cranking, although once cranking it sped up a lot, in pulses. Is this expected? Fuel was also flowing through the return line at pretty much all times. If there’s some easy things to check or fix regarding fuel pump, regulator, etc, we’ll try them with the flat tops first, or otherwise, if the carbs seem to be the issue, we’ll order a service kit for the round tops and get to work on them. Lachlan