Carburetor Conundrum (260Z)

[Racer X]

On 7/11/2022 at 12:02 PM, DadAndLadZ said:This is the one real drawback to these sidedraft units…you can’t see down em! Much obliged.

If you need to look into the throttle bores, a mirror will work. A light will make it even easier to see.

[Racer X]

On 7/16/2022 at 7:34 PM, DadAndLadZ said:

Just using some motor oil, I think it’s like 10W40. As far as I can tell it’s staying in there, I haven’t seen it leaking anywhere. 

I believe the FSM. Calls for 10wt non detergent motor oil.

I use ATF, and usually only a few drops.

 

[Mark Maras]

 I remembered 20wt. being used but the oil just slows the piston rise during acceleration. With the butterfly open and the piston slowly rising the air speed thru the venturi speeds up drawing more fuel from the bowl.

[Racer X]

OK, I just read through the entire nail in the vacuum port saga, and would like to offer some observations.

In the first post there is a video, and you have your son start the car. You direct him to pump the accelerator twice before cranking the engine. This is a common misconception carried over from engines equipped with carburetors with automatic chokes and accelerator pump circuits. Stepping on the pedal before starting does two things. First, it allows the choke plates to fall closed. Second, it squirts a bit of fuel into the intake passage.

This does nothing with the SU carburetor, as it has no accelerator pump circuit and no fuel will be introduced prior to startup. Also, the SU carbs don’t have a choke plate, the “choke” lever simply opens the throttle slightly to facilitate more air and extra fuel (only added as the pistons draw air through the carbs into the engine, which also draws fuel from the float chamber through the orifice where the tapered needle is in the carb throat).

I also didn’t see and mention to check for vacuum leaks (although Mark Maras did mention that excess air, not fuel, will cause high idle). 
 

Ultimately the culprit was found to be a hack job by the previous owner who did the carb conversion.

 

My .02 cents.

 

[siteunseen]

That's what makes this forum work so well. A lot of experiences thrown at the problem and 1 or two stick, also known as the shotgun approach.

 

[Racer X]

It may be possible to repair the vacuum port that had the nail in it, with an appropriately sized brass tube. Use a tube that is slightly too big, and turn it down, then press it in.

Not sure what to do about those cobbled up throttle shafts with the “inject grease here” scratched into the flanges. Perhaps the place in Oregon, Z Therapy could repair them. They have a ball bearing upgrade for the SU carb.

 

[Captain Obvious]

I wouldn't worry about the grease holes. They'll be sealed up by the gasket on the mounting face. And if you don't tell anyone about them, nobody will ever know.   

And about that hole for the ported vacuum... If one were to assume that the previous owner drilled the original vacuum nipple out of the carb body, and did it "concentric to the original center of the hole", then one could make an insert with the appropriate diameter small hole through it*. Press or loctite it in place and very carefully file the inside flush with the curved surface of the carb throat.

I could do it. At least if the center line of the enlarged hole is in the same location as the center line of the original port hole. If they ham handed the removal of the original tube and drilled off center or something, then the location of the new port will be mis-located accordingly.

 

* Or get extremely lucky and find some piece of tubing off the shelf that already has the correct ID and OD. Extremely lucky....   

[Racer X]

On 7/7/2022 at 10:45 AM, DadAndLadZ said:I have not actually checked the fuel pressure and not sure how to do that?

Sorry, I meant to comment on this earlier.

A good quality gauge and a proper fuel pressure regulator.

The red Holley fuel pressure regulator works well, and has two outlets, or to go to the carbs, the other where a gauge can be connected.

The SU carbs don’t require much fuel pressure, under 4psi if memory serves me.

A picture of the setup on my race Z: