Weber settings/jets for a 3.0?

[haycait911]

OK, I've searched for the last 20 minutes and no joy. using 40 IDA's.

building a 3.0 with stock CIS pistons, stock cams, small port heads, SSI's, and Weber IDA's. can someone give me an idea for a starting point to set up the carbs? I know I could use better cams and pistons but it's not in the card$ right now. anyone who is running a similar set-up I would appreciate hearing what jets/settings you're using. thanks, Don.

[Hotrod911T]

Don,

This may not be a big help because I have a feeling you have Weber 40IDA's, although you didn't mention the carb size in your thread. My son has a 3.0 similar to your build, however with Weber 46IDA's. The specs of his carbs as set up by PMO are 55 idle jets, 150 main jets, 180 air correction jets, F3 emulsion tubes, 4.5 tall aux. venturiis, and 36 mm venturiis. I am using 46 PMO's on my 2.7 so those settings won't be of help to you.

On some old correspondence I have from PMO, for a 2.7 with 40IDA's and 34 vens, it suggests 145 mains, 180 airs, 60 idles, and F3 e. tubes. Using 36 vens, it suggests 155 mains, 175 air jets, 60 idle jets, F3 e. tubes and tall AV's. I don't have any of PMO's specs for a 3.0 using 40IDA's because they are a little on the small size for a 3.0 and most people are probably using 46IDA's. Go to PMO's website and read the section on adjusting and tuning carbs for more info.

If you don't have it already, one thing you will most probably need if you are going to run the Weber carbs is a high energy CD ignition such as an MSD 6A or Crane HI-6, which will help to eliminate "carb problems" such as flat spots and poor throttle transition.

Rod

[SCrescue]

Don,
From Bruce Anderson's book (Porsche 911 Performance Handbook, pg 134), the recommended starting setup for 40IDA-3C on stock 3.0 with exhaust back date is as follows:

34mm venturis, F3 emulsion tubes, 160 main jets, 175 air-correction jets, 60 or 65 idle jets.

Hope this helps.

Mike

[haycait911]

thanks guys.
Rod, will the Crane or MSD work with the stock dist. and replace the stock CDI box?

[shbop]

I'm running a 3.0 with 40 IDA's, crank fire ignition, and I found Bruce's recomendations to be way off. I ended up with 145 main, 180 air, and 55 idle.
I started with the recomended stuff. Way to rich where I am.

[Hotrod911T]

Don,

Yes, both the MSD and Crane CD units will work with the standard points-type distributor. I ran a stock early 1967 911S distributor with an MSD 6A and MSD coil for years. Now I am using the Crane HI-6 and matching Crane coil with the distributor, except that the points have been replaced with a Pertronix Ignitor electronic module. The stock points worked fine as long as you have them properly adjusted.

Rod

[haycait911]

Rod, my 3.0 has an electronic pick-up sensor wheel in the dist. still use a Crane/MSD?

[Hotrod911T]

Don,

I don't think there will be a problem because these ignition units can be triggered by points, electronic, magnetic, or whatever triggering device. If you check on the MSD Ignition or Crane websites, there should be the installation instructions for both of these units for your type of distributor.

I personally changed to the Crane HI-6 because it is a digital unit with built-in rev limiter that can be adjusted internally without the rpm "pills" used in the MSD 6AL. The 6A unit does not have an internal rev limiter. I also am using the matching Crane PS92 coil and Magnecor ignition wires. I have set the rev limiter for my 2.7 at 7,300 rpm, but the ignition system should work fine to well over 8,000 rpm. The acceleration and throttle response is crisp throughout the rpm range.

Rod

[sozaysven]

Is it easy enough to change all these jets with the carbs in the car? I am guessing it's done since guys I believe tune jets at the track. But just wondering if home tuners who aren't optimised for the track usually pull the system off instead of working with small jets with arms stretched into the engine compartment. Seems like you would need a stack of intake gaskets if that was the case.
Thanks,
Adam

[juanbenae]

you can get to everything with them installed. that's one of the advantages of carbs in that they provide a uncluttered engine compartment.

[Trackrash]

Originally Posted by sozaysven

Is it easy enough to change all these jets with the carbs in the car? I am guessing it's done since guys I believe tune jets at the track. But just wondering if home tuners who aren't optimised for the track usually pull the system off instead of working with small jets with arms stretched into the engine compartment. Seems like you would need a stack of intake gaskets if that was the case.
Thanks,
Adam

Is this a rhetorical question? I am guessing you have never R&Rd Webers or changed their jets.