123 Ignition help 71 911S

[jameshurst71t]

Hi guys, the situation is I have a street car 1971 911T rebuilt to S with PMo and 123 Ignition Tune + Bluetooth . I consistently have black plugs, fouling number 4, heavy pops under decel and poor running below 3000 RPm. I’m struggling with timing this motor and tuning these carbs.

Engine is newish and compression checks out at 149 across the board. Dynoed at 200hp. I have hot Solex cams. My PMOs are 130 jets, 200 air, F16 and 60 idles. I have unburnt fuel at low RPM. They balance at 7. The local tuner is not a believer in 123 so I’m on my own and need your help.

[jameshurst71t]

Here is s curve

[rowingone]

I have a stock 72 911T MFI and use Ian's curve (Icarp) with good success.

no map

[rowingone]

Here's a driving video

https://www.youtube.com/watch?v=klKPc17CBdo

[jameshurst71t]

Thanks RowingOne! What’s your map curve look like?

I wonder how, if at all mine would be different since higher compression?

[rowingone]

Ian told me no map so all at zero there.

[rowingone]

Don't over think it . . start with Ians curves and adjust from there.

[jameshurst71t]

Well that’s 2x times better. Thanks! Still some popping and low RPM shuddering/hesitation so I swapped .60 idle jets for .55.

Here are the temps:
1: 215F brand new NGK8 plug
2: 220F NGk7
3: 208F NgK 7

4:200 (brand new NGK8
5: 170 NGK7
6: 178 NGK7

I will disconnect linkage to confirm carbs are balanced. I think they are 7kgh.

I saw a p a r tz k lassik video where he had a 70T at 4.5 kg/h
https://youtu.be/NLrzElDL9rc?si=IvTHm_d9m9mlmt3V

[jameshurst71t]

Now car can’t hold idle. Any suggestions?

https://youtube.com/shorts/G6BMPp5speU?si=AL22Xd5zoeKn4hzy

[snbush67]

Was the engine warmed or cold when it was low idle and stalled? That’s normal for a cold motor.

Warm the car and set the idle screws equal at 800 rpms (or higher to keep it running) Then using the 123 tuning app add or subtract 1-2 degrees to increase and smooth the idle. You can’t save the curve while tuning, once you know what adjustments are desired turn the car off and then edit the curve (or make a new curve file) and write it to the 123.

What size chokes vents are in the PMO’s?

[jameshurst71t]

When warm, car stutters at low RPM and detonates heavily on decel. I’ve had it for 25 years and have had ignition issues since rebuild. Plugs are black and oily and smell like gas.

I run NGK 6 or 7 or Bosch based upon what’s available. Currently NGK7

[Bob Ashlock]

With the 123 distributor, are you using it to trigger the CDI box with factory Bosch low inductance CDI coil, or has the CDI been bypassed and you are just having the 123 directly fire a high inductance coil? If so, what coil? (wanting to make sure not the old CDI coil I hope as that would be a big problem!). Also, in my opinion the idle jet size of 60 seems excessive and will create an over-rich situation at idle and low rpms, and will contribute to popping on decel. I would think 55 idle jets might help.

[47silver]

What Bob asked

[jameshurst71t]

Hi Bob. I swapped in 0.55 idle jets. I’m using 123 ignition with 123 ignition coil. My rebuilt CDI box is in a box. I replaced all plugs today and balanced the PMOs. It’s backfiring pretty hard on decel and fouling lots of plugs. Lots of unburnt fuel at low RPM. We are going to take a timing light to it to verify the timing is what 123 app says it is. I have clewett wires fwiw. It’s frustrating.

[rowingone]

I have a 72 MFI with the 123 and was having plugs foul . . .I was told on this forum I didn't need to run the CDI box with the 123 . . wrong! . . hooked the CDI back up and solved my fouling plugs problem.

[snbush67]

Originally Posted by rowingone

I have a 72 MFI with the 123 and was having plugs foul . . .I was told on this forum I didn't need to run the CDI box with the 123 . . wrong! . . hooked the CDI back up and solved my fouling plugs problem.

What coil were you using with just the 123 direct to the coil?

[47silver]

Try it with the cdi. Our 72. Mfi uses 123 with msd and is fine

[mysocal911]

Originally Posted by rowingone

I have a 72 MFI with the 123 and was having plugs foul . . .I was told on this forum I didn't need to run the CDI box with the 123 . . wrong! . . hooked the CDI back up and solved my fouling plugs problem.

Read here starting with post #35; https://forums.pelicanparts.com/porsche-911-technical-forum/1176775-123-distributor-911sc.html

[47silver]

Never tried it without the cdi, wanted a new distributor that allowed curve fitting via blue tooth. If cdi gores kaput a matter of changing a couple wires.

[PeteKz]

47Silver: If you are using the 123 dizzy with the Bosch CDI, and the CDI goes kaput, it is NOT a "matter of changing a couple wires" (to get running again). The Bosch CDI coil is a low impedance coil, with a primary basic resistance of about 0.3 ohm. The instructions with the 123 specifically warn not to use a coil with less than 1 ohm primary resistance. That would increase the current flow through the transistors in the 123, eventually leading to failure. If the Bosch CDI dies, you must remove the Bosch coil and swap in a coil with more than 1 Ohm primary resistance. FYI, the 123 coil primary resistance is 1.5 Ohms.