Christmas Build, 3.2 Short Stroke, 10.1 CR

[ToySnakePMC]

Congratulations! Glad to see that she's up and running. As someone who has yet to do the first start on a full rebuild / "while you're in there... / upgraded components - I cannot imagine your sense of relief and smile on your face when all is well at start up. Beautiful engine bay, wiring, and Targa. Please share more pics of car and engine bay. Love it. Patrick

[Old H2S]

Shane, I ran F3 then to a F7 and now I am running F24's.
Keep the up dates coming..

[snbush67]

Originally Posted by Old H2S

Shane, I ran F3 then to a F7 and now I am running F24's.
Keep the up dates coming..

F24’s, that’s what they used in the 906.

I’m making progress, went down to a 55 idle jet, part throttle light cruise is at 13.4, which is nice. But now I have a couple of lean bumps during normal acceleration that I have to fill in. The lean gaps are between the idle to progression and progression as the mains are kicking in.

All of the sudden I remembered that the idle circuit gets tuned first, and that part throttle light cruise is 95% Idle circuit, 5% progression, and 0% main.

[Glenfield]

Going down this path myself albeit with far less success. Idle can influence AFRs up to 4500-5000RPM in light cruise. Did you move to F7? Think that brings main in sooner if leaning out bc of RPM alone (so gradual acceleration keeping out of fuel enrichment pump). Otherwise maybe fuel enrichment pump?

[Old H2S]

Half a turn on the accelerator pump shaft made the low end happy, the F7 made the transfer to the main happy but the WOT was off at 7k so now I am trying out the f24 which is made for mashing it out of corners.
I disagree on the steps now. On first set up start at idle and work up the RPM. For WOT tune with emulsion tubes and the clean up the bad RPM spots.
I am dealing with battery, dead fuel pump, dead starter right now so Friday I might have some more numbers for you..

[snbush67]

Originally Posted by Glenfield

Going down this path myself albeit with far less success. Idle can influence AFRs up to 4500-5000RPM in light cruise. Did you move to F7? Think that brings main in sooner if leaning out bc of RPM alone (so gradual acceleration keeping out of fuel enrichment pump). Otherwise maybe fuel enrichment pump?

Yes, F7. The lean spots are only with slow acceleration. The pump jets are doing well with rapid acceleration.

[snbush67]

Originally Posted by ToySnakePMC

Congratulations! Glad to see that she's up and running. As someone who has yet to do the first start on a full rebuild / "while you're in there... / upgraded components - I cannot imagine your sense of relief and smile on your face when all is well at start up. Beautiful engine bay, wiring, and Targa. Please share more pics of car and engine bay. Love it. Patrick

Yes, start up was nice. The twin plug is magical! I’m not sure if anyone else has ever used a 123 distributor with a CCW rotation to fire a twin plug but it’s working great for me.

[Rosco_NZ]

I’m in the process of building a twin plug distributor using a Marelli body … will post some progress updates in another thread

[snbush67]

Originally Posted by Rosco_NZ

I’m in the process of building a twin plug distributor using a Marelli body … will post some progress updates in another thread

That’s great! I look forward to following along.

[snbush67]

I’m working on a chart showing a basic generalization of the circuits and the contribution throughout a slow acceleration without pump jet enrichment. I think that it’s close. The progression circuit is probably a bit too steep in the beginning, probably close.

[Glenfield]

I'm having to come up the curve quicker than I'd like on carbs but I think of the idle and progression circuit as functionally the same circuit. Idle/progression blends into main ... where and how it blends, depends on:
- position of throttle valve vis-a-vis progression holes ... too exposed at idle and it brings in main circuit sooner (not your condition)
- size of idle air corrector (or maybe even idle jet) ... this could be it but I'd h have expected it deeper into RPMs. If it's too small, it may lean our idle/progression circuit at higher RPMs within the idle/progression circuit
- idle mixture screw ... if too far in to get idle AFRs acceptable, it leans out the air/fuel mix flowing through the progression holes which will bite right before mains takeover
- emulsion tube ... when it brings in mains as you described above.

I could have that all wrong but it is my best attempt at unpacking the theory.

[snbush67]

Originally Posted by Old H2S

Half a turn on the accelerator pump shaft made the low end happy, the F7 made the transfer to the main happy but the WOT was off at 7k so now I am trying out the f24 which is made for mashing it out of corners.
I disagree on the steps now. On first set up start at idle and work up the RPM. For WOT tune with emulsion tubes and the clean up the bad RPM spots.
I am dealing with battery, dead fuel pump, dead starter right now so Friday I might have some more numbers for you..

I think the only way to clean up a lower rpm lean spot as progression is coming on is to use smaller chokes to increase the signal strength, or to richen the idle using bigger idle jets or adjusting the mix richer. I don’t think the main circuit contribution is significant at the lower rpm. Sacrifice a bit of fuel mileage to run smoothly. It’s about finding the balanced sweet spot.

It really is all about signal strength, I’m sure the 38’s you sent me would be an easy fix. I’m still trying the 40’s. Ian really believes the 42’s would be perfect.

[Old H2S]

Use what you have.. I am running 38's with a smaller cam and I pull to 7k now easily and have the 123 dizzy set for a 7200 cut out.
I ordered some F66 emulsion tubes to see what those run like?

[snbush67]

Success. —— 46 PMO with 40 Chokes

57 idle jets, F11 Tubes, 185 Mains, 205 Airs.

Tuned to 13.4 AFR at 950 rpm idle, light part throttle cruise is 12.6 at 2900-3100 rpm, to 6800 rpm is 12.6.

This is a plug that’s been through all the tuning, it’s cleaning up nicely with the right tune.

[Glenfield]

Congratulations! Got to be happy with that.

Curious what plug and heat range you’re running?

[PeteKz]

That's a good-looking spark plug.

[snbush67]

Originally Posted by Glenfield

Congratulations! Got to be happy with that.

Curious what plug and heat range you’re running?

Top plugs are NGK BPR8ES 14mm hole
Bottom plugs are NGK D8EA 12mm hole

[snbush67]

Originally Posted by PeteKz

That's a good-looking spark plug.

Thanks Pete! That means a lot. I sent the picture to Ian and he said the same.

[PeteKz]

If it looked any better I could lick it!

[snbush67]

Originally Posted by PeteKz

If it looked any better I could lick it!

I did, it was an unsweet, dry, light, charred mocha with a strong mineral finish. Not an hint of unburned fuel or a trace of oil. Exactly as expected.