40 ida main jets

[1976 TN Porsche]

Does anybody make a idle jet between 60 and65. It seems that 60s are to small but 65s are to big. Any help would be Great. Thanks.

[chris_seven]

Do you mean main jets?

Standard main jets range between 110 for aa IDT fitted to a 2/0 litre T and 135 for an IDS fitted to a 2.0 litre 911S

60-65 sounds a bit small

[1976 TN Porsche]

Sorry I ment idle jets. Thanks

[Porsche Doc]

Go with the 65's and adjust with the Idle mixture screws.

[1QuickS]

You could tweek them with a jet reamer or redrill using:[LIST]

• #73 drill = 61 idle jet
• #72 drill = 63.5 idle jet

You would need a pin vise to hold the bits; also it would be good to sand off the OEM size marking and metal etch (vibra-etch) the new size.

[1976 TN Porsche]

Thanks Guys.

[Brant]

The idles just aren't that critical/sensitive
its really the redline that matters.

but idles do effect across the whole range
so run either one and adjust your main jets to what ever is best at redline.

what symptoms are you trying to fix?
if your fouling plugs or something... I would look more at the transition (accelerator jet volume, E-tubes, or airs)

you can also add air correction size to the problem and attack things from that angle.

brant

[1976 TN Porsche]

It runs rich at idle. It seems to load up with the 65s but runs better with the 65s than the 60s. It is a stock 3.2 with Weber 40 IDAs 38 ventures, F26 emulsion tubes, 160 airs, 65 idles, 160 mains. Rebushed by Paul Abbott at Performance Oriented.

[TimT]

The engine runs on the idle jets to somewhere around 3000rpm depending on air corrector and emulsion tubes..

Using jet reamers has proven to be helpful..

[1QuickS]

I'm guessing that with 38mm venturis you have a difficult time transitioning onto the main circuit which is why the large idle jets help enrich the transition at the expense of rich idle circuit. If so then one thing to try is to raise the fuel level a couple of mm above the top line of the fuel level sight gauge and install 60 idle jets. Be sure your fuel pressure is 3.5 psi at the inlets to the carbs.

Raising the fuel level advances when the main circuit is activated.

Alternately you might consider going to 36mm venturis, the 38's are a little big for a stock 3.2 and down sizing the venturis would allow for a smaller idle jet size since the signal for activating the mains would be stronger and earlier.

Main jets affect mixture strength from transition through redline; emulsion tubes affect when the mains become active and how fuel is metered from transition through redline and the air correction jets adjust mixture strength at upper RPM operation. Idle jets with their own air correction jets and the position/size of the progression hole drilling affect mixture from idle through transition. Transition is the cross-over point where the idle circuit becomes less effective and the main circuit becomes activated; the mixture during transition is the resulting sum of idle mixture (diminishing as RPM rises) plus main circuit mixture (increasing as RPM rises.)