The car had originally 55F8 idle jets. With the aforementioned issues that I attribute to a bit of a lean condition...

I tried a leaner jet 50F9 - which should have made things worse, and they did

I tried a richer jet 60F9 - which should have made things better, and they did

The problem is the F9 runs marginally richer than the F8 given the same fuel orifice per weber documentation:

Rich - F6 F12 F9 F8 F11 F13 F2 F4 F5 F7 Fl F3 - Lean

So the 50F9 could have been much closer to the 55F8 than I wanted, which makes sense as the results were only slightly worse.

Likewise, the 60F9 was probably two many steps to the rich side as I think she is burning a bit rich on throttle application, but I have zero hesitation or stumbling.

What I should try is a 55F9 or a 60F8

Oh the joy of this job.

Things will be much clearer when I install my sideband

Personally, my money is on the 55F9, but I ordered both just to be sure.

Edited June 1, 201410 yr by Zedyone_kenobi

Interesting observations.

Sadly today, I spent a few hours fighting with the 510's ignition and did not have time to experiment and collect data as promised.... I only had time to stop fouling plugs with jet change.

When I started playing with Webers a couple of years ago, I characterized an idle jet's performance by measuring A/F ratio at idle vs. at cruise (both places are where it works) at different turn-outs of the idle enrichment screw. My goal was ~ 14.0 at idle and 15 at cruise with 12.5 in the high rpm range.

[Digression, I ran into problems due to fuel level and the mains clouding the cruise. I hope to have another battle this summer.]

Here are typical plots:

In the above data I drilled out the air hole on the 55F9 to 1.5mm. I got 14 idle with 13.6 cruise.

The 55F11 idle jet shown also gave 14 idle with 13.6 cruise. So I made a "richer" F9 perform like a "leaner" F11 by giving it more air.

Here is the same data for the drilled F9 presented slightly differently.

Here are the dimensions of Weber Idle Jets in case you wish to drink and drill

Edited June 2, 201410 yr by Blue

I found a lot of that by researching a bunch of our old DCOE posts blue. I think you and I should write a book one day!

Thanks! I need to collect data first.

The 510 will be the test bed because it is faster to change 4 jets rather than 6 on the Z

I hope to plot air holes vs Air fuel and experiment to develop a model. I will pull out the drills soon. I hope to compare 4 air holes with 2 air holes with 1 to see if symmetry at the idle jet makes a difference. I'll also try inserting tiny venturi chokes in the jets as well as moving the air holes up and down..... fun fun fun.

You should be able to experiment with solder and drilling to your needs then have a final set of new small holed jets such as 40F5's (essential blanks with pilot holes ) drilled to your experimental set's specs.

btw did you see my PM? Please email me and I'll send you the Weber Guru's notes.

Edited June 2, 201410 yr by Blue

I did email you... or so I thought.

It went to junk mail... all is sorted now.

Installed my 60F8 jets this afternoon after work. Car did not like the mixture ratio. It felt rich, but when the idles screws were adjusted to get the best (read as fastest) idle, the car stumbled in every gear and still had bad popping through the exhaust.

Then I installed the 55F9's. Wow, such a small change and what a difference. The car settled into a very smooth idle, I could not make it stumble with clumsy launches or wide open throttle openings or barely applying any gas and letting the clutch out too fast. The car just is just thrilled with this mixture.

Now I will say this as well. And this is interesting!

While I was putting my jets in, the FedEx truck came by. And dropped off my NOS OEM 68 datsun seat covers. They are just stunning. But with them I ordered 4 new oil filters and 8 new NGK BPR6ES plugs.

So after I put in 55F9s in the car I went ahead and installed my new NGK plugs (gapped to .035"). The car had Autolites in it (PUKE!!!)

But the way that baby climbs to 6000 rpm is just glorious. It is seamless. Makes me wonder if it was the autolites or the jets. Happy to report that the 2000 feels like a race car now.