240260280

The A15 has 32mm chokes. You tested 34mm, 35mm and 36mm with the same shape of wot run so it seems independent of nearly every parameter. Hopefully higher fuel level will help.

No need to rush. They did not discuss the a/f on the site. It was a race site so I am surprised to see this wide range of leaner excursions to 14.

For information: Here is a WOT dyno run for a Datsun 4 Cylinder with A15 engine and dual 45DCOE with 32mm chokes. A/F ratio shape from start to 6000 seems similar to yours but with 4.5 point spread.

Good Eyes! Almost. Here is the original I used above c/o Kats: https://www.classiczcars.com/forums/topic/22141-my-clollection/?tab=comments#comment-323796 This is also the same car in the Maintenance Manual that Kats posted. You can see the light coloured fuel hose in this photo c/o Kats Here is another from Kats with better clarity. The fuels hoses are very light and the dist. cap is green. The strange 3rd hose from the fuel rail is there.

A comment on using only water. The pressure exerted by the water in the hose pushing down on the fuel needle to open it is 33% more than gasoline (assuming density of gas is 750kg/m^3) The pressure exerted by the fuel float pushing up to close the fuel needle valve is ~ 33% more in water than in gasoline. So using water is not very inaccurate as the two forces nearly cancel each other. The key point in using water is to use the table above to get ~3.4psi of head.

Good point. I recall a coolant hardline that wrapped around the back of the head for running coolant through later manifolds but did it terminate so high up where the fuel rail is and was it on early models?

Water Column Height (Head) to PSI at sea level. 240z pump output pressure is 3.4PSI so use ~7' 11" for Weber bowls or stock SU bowls. If you use an electric pump and external pressure regulator, dial the regulator to 3.5psi and use 8' If you use gas in the hose rather than water, multiply the psi in the table below by 0.75. You will need ~10.5' of gas head to get 3.4psi.

Hi Kats, Another mystery ? I re-coloured one of the red photos from the service manual. I hope you enjoy it. In doing so, I noticed two unusual features that did not make it to production. 1. The fuel rail to carb hoses are very light in colour (not black). 2. There seem to be three of these hoses coming from the rail rather than just two. ( 1 to the front fuel bowl, 1 to the rear fuel bowl, 1 that seems to go to the fuel bowl area [see second picture]) Any idea on what material the hoses are made and the purpose of the third hose?

Good questions young grasshopper! You are correct. In general,carbs work by venturi vacuum (often called depression) lifting fuel from the surface and pulling it into the throat. In the DCOE, the idle circuit, progression circuit and the main circuit all do this. The amount of fuel lifted is proportionate to the fuel level. If it is too low, no fuel will be lifted. If it is too high 100% fuel will be pulled and no air (except what is coming down the throat). Adjusting the fuel level in a DCOE is not a fun job but once it is done it rarely changes. Here are two ways to do it, I recommend the second: On car: 0. remove plugs 1. remove fuel lines to a carb 2. remove screws holding that carb's lid 3. lift lid and bend tab 4. siphon some fuel out of bowl to lower level 5. install lid (often two screws are fine) 6. connect fuel hoses 7. run starter to fill bowl 8. measure fuel level 9. if not at target (27mm) repeat 1 to 9 10. Repeat for all 3 carbs Off car: Get a friend, a ladder, hose, gasoline (water works but gas is more accurate), a clear plastic bowl, and an area with a high roof. Do this: https://www.classiczcars.com/forums/topic/52084-setting-fuel-level-weber-dcoe/ Note: floating the bowl in gas will be more accurate for the level however the 8.5 to 9 foot head of water will give the right pressure on the valve, so gas in the bowl and water in the hose for best results. I just used water and the result was all 3 carbs were the same level. When I put the carbs back on the car and ran the engine, they all measured the same level which I think was ~ my target. Memory is not what it used to be. If you use fuel in the hose, 10.5' of head will give 3.4psi at the carb's needle valve.

Here is a picture of the engine compartment of one of the earliest 240z's. Date would be ~ Aug-Sept 1969. You can see the air filter housing colour is like yours. Spare parts housings were also reported to be delivered in this colour.

Good data. This may be why the WOT run is not flat for all Etubes. Could you please raise the fuel to 27mm down and leave the existing parts in. It will enrich all circuits so be aware. It would be good to see what it does to the WOT shape before dialing back the fuel jets. Hopefully the shape will change.

Jeff, FYI:here is a long thread on optimizing 45DCOE's on an L28. We are getting closer to a final optimized state but there is one unfavourable parameter we have not been able to tune out yet . Hopefully we will get it resolved before you go to triple 45's so that it can help in tuning your application. https://www.classiczcars.com/forums/topic/56375-weber-selection-and-initial-jet-tuning/

Maybe it was to protect the bearing from over torque, i.e. the copper would compress if the torque or a force exceeded the max torque spec. Sort of a sacrificial "bumper".

(dip stick) Or you can stick a wire tie down the main jet tube to the bottom then mark where the top of the bridge is and measure from it to the wet point.

Here is another (optical): Optical_Tool_Turning_Dark.MPG Optical_Tool_Turning_Dark.MPG

Here is another (pipet):

Yes. Here is a quick way to do it:

Before you make any changes. What is your current fuel level? What is troubling is the 3 point range of the WOT runs that we can not remove with E tube change or accelerator circuit. The Venturi size or ratio of venturi to throat (or fuel level) could be part of this seemingly untunable undesirable curve. It needs to be explored further. FYI It looks like the accelerator pump circuit removal leaned the top end out ~ 1 point. The big dip at the first 1/3 of the WOT run is the gorilla in the room. Hopefully fuel level lowering can remove it.

Lovely Thread! I rate it 5 monkeys! ?????

240z needle valve is 2.0mm (below). I can not find data for 260z.

I may have a few kicking around.

If you use 45's then consider a 33 or 34mm choke. The transition from the 33mm choke to the larger 45mm throat (vs 40mm throat) is the challenging tuning aspect to address according to Passini (fuel will precipitate). Below is a table I made to help fit side-draft carbs to Datsun I6 Engines of different displacements and 6500rpm redline. The red trace is for racing applications and is taken from the Weber's formula. The blue line is extrapolated for street. 3 real-world data points are plotted to validate the extrapolation. For an L28 street application, a 40DCOE with 32 or 33 mm choke is the ideal. For 50DCOE racing and running at a 6500 redline, one will need a 3.4litre displacement engine. note for racers: Operating at higher RPM's than 6500 pushes the red line up.

Check the block breather to pcv hose. They go soft and gummy. Your z has the improved AAR hose routing so that is good too. This will get you into trouble: http://atlanticz.ca/zclub/techtips/efisystem/overview.html http://atlanticz.ca/zclub/techtips/electricalconnections/index.html

Love it. I have some 280z parts I can send. I 'm pretty sure I have those elbows to the throttle body.

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