Cis to Carbs...documented power increase

[Aztim]

Run a pmo pressure regulator when swapping from cis to carbs, it is designed for exactly that and takes care of all of your questions

[930cabman]

Originally Posted by snbush67

That really depends on if all of the components are there and working properly. If you just need to clean it and refresh some rubber pieces than yes. If your air box is cracked, wur is out of spec, fuel distributor needs rebuilt, etc. it can add up quickly.

Exactly where I am at today. I have this cool, partly original 1975 911S that never leaves the garage. I am sure when the CIS was new, it was the best for a street machine, but after 1/2 century and who knows how many sets of hands, my CIS has seen much better days. She starts hard (cold), bucks/surges between 2k and 3k rpms. That and the fact I know Webers well and have an extra set on the shelf, I know whats involved. Anybody looking for a used CIS for parts

[PeteKz]

Get in touch with Tony and send him your FD and WUR for testing and adjusting before you throw in the towel on CIS. If you still decide to give up, Tony usually buys CIS stuff.

If you already have a set of IDTP's, including all the manifolds, linkage, air cleaner, etc., then I guess those won't be Weber expensive. But you will have to spend some money for jets and time dialing them in for your engine.

[930cabman]

Originally Posted by PeteKz

Get in touch with Tony and send him your FD and WUR for testing and adjusting before you throw in the towel on CIS. If you still decide to give up, Tony usually buys CIS stuff.

If you already have a set of IDTP's, including all the manifolds, linkage, air cleaner, etc., then I guess those won't be Weber expensive. But you will have to spend some money for jets and time dialing them in for your engine.

I have tried Tony without a positive result, towel is in lid flight. Even if I got the CIS going with (x) expense, it will require some level of maintenance.

Yes, the Webers I have are in good condition, but will need manifolds and some other bits (Pierce), but Webers are a known object for me, CIS is very unknown

[PeteKz]

I haven't seen Tony reply for about a week. He might be traveling or doing some other stuff.

[Old H2S]

I have had 4 different types of induction on my engine so far..
-Stock CIS in good working order, I know the system well. As you fix and replace parts it gets better, but what a price tag now for used parts from German junk yards, and new taxes.
-ICARP CIS, adjustable output for modified engines. Yes you have to look at an AFR gauge and turn a dial.. big deal, any AFR you want, after a week you will leave it alone and get GREAT gas milage if that's your bag.
-Holley NASCAR 500 CFM 2 bbl. Starts on one cog of the starter every time hot or cold, pulls like a turbo, lots of fun with skinny tires. Might try the Sniper 2 next time.
-New Weber 46 IDA C3's, expensive, classic, a b*tch until tuned then bliss.. I just did 1000 miles in one day last week, after the math I got 28.3 MPG @ 82MPH average speed, I was blasting the car from Sarasota to Buxton. They really need the the 123 distributor to come alive and all your buddies here to help with the jetting. Good parts are expensive.

[930cabman]

Originally Posted by Old H2S

I have had 4 different types of induction on my engine so far..
-Stock CIS in good working order, I know the system well. As you fix and replace parts it gets better, but what a price tag now for used parts from German junk yards, and new taxes.
-ICARP CIS, adjustable output for modified engines. Yes you have to look at an AFR gauge and turn a dial.. big deal, any AFR you want, after a week you will leave it alone and get GREAT gas milage if that's your bag.
-Holley NASCAR 500 CFM 2 bbl. Starts on one cog of the starter every time hot or cold, pulls like a turbo, lots of fun with skinny tires. Might try the Sniper 2 next time.
-New Weber 46 IDA C3's, expensive, classic, a b*tch until tuned then bliss.. I just did 1000 miles in one day last week, after the math I got 28.3 MPG @ 82MPH average speed, I was blasting the car from Sarasota to Buxton. They really need the the 123 distributor to come alive and all your buddies here to help with the jetting. Good parts are expensive.

Cool, which is the winner?

I have never used an AFR, but reading spark plugs works just fine for me

[Old H2S]

The most fun is the Holley by far. Even being just a 2 bbl it has that Wa-WAAA when you kick it and the power valve opens. Cons.. crappy MPG. Just have to keep your foot out of it, but it is easy to tune and the amount of aftermarket parts and new designs will keep this carb up to date for a long time compared to the Weber which is 60 years old design but very smooth. The Weber is tunable for any engine BUT that doesn't mean easy.. It is too adjustable and very touchy, .1mm change and that jet is now too big and your down the rabbit hole.. I am surprised at the MPG I got. Do you know how fast I was going to get 82 MPH average? People in Florida drive like their hair is on fire.
PMO's would be better but they have to up their game, I hear the early ones were best. Too bad Paul has retired and now it is up to us here to help each other out. How long is Henry, William, Neil going to last? We are working on antiques and have priced ourselves out of the market on a low volume toy.
To all, no matter what you run, carbs, CIS, MFI,EFI, all the new stand alone systems, get a fast AFR gauge from NTK and you will see how slow your system really responds.

[PeteKz]

Originally Posted by 930cabman

Cool, which is the winner?

I have never used an AFR, but reading spark plugs works just fine for me

You can't read your plugs while driving down the road. You can read the AFR meter. However, it might tell you stuff that you don't want to know.

[930cabman]

Got the twin Webers installed and they seem great. This 1975 model has a vacuum can and this no longer needed/wanted.

Is there a recommended distributor for this conversion? 123 might be an option, but I am considering a late '60's point distributor for simplicity. The 123 is probably too high tech for me (old guy)

I am thinking 35 degrees +/- at 6000 rpms is the desired spark timing?

[PeteKz]

You want a vacuum advance on your dizzy. You need more advance at part throttle for drivability and fuel efficiency, and less at full throttle to prevent detonation. Even the 123 has a vacuum sensor for vacuum advance.

[930cabman]

Originally Posted by PeteKz

You want a vacuum advance on your dizzy. You need more advance at part throttle for drivability and fuel efficiency, and less at full throttle to prevent detonation. Even the 123 has a vacuum sensor for vacuum advance.

Agreed, vacuum advance is a good thing. Not sure where to receive a good signal above the throttle plate? as far as I know Webers are not available for this

[PeteKz]

vacuum signal must come from below the throttle plates. Later smog-controlled engines used various "port vacuum" for distributors designed for emissions, but you should use manifold vacuum for starting your setup. I don't know where ythat is available on your carb and manifold setup. Send a picture?

[930cabman]

Originally Posted by PeteKz

vacuum signal must come from below the throttle plates. Later smog-controlled engines used various "port vacuum" for distributors designed for emissions, but you should use manifold vacuum for starting your setup. I don't know where ythat is available on your carb and manifold setup. Send a picture?

Learn something every day, my thought was to tap for vacuum above the throttle plate, finding vacuum below the plate is easy.

Won't the advance always be activated once the engine is started if always drawing vacuum?

thanks

[PeteKz]

Only during high vacuum conditions, such as idle or cruising. As the throttle opens, vacuum decreases quickly and advance is reduced. The vacuum pod and springs in the dizzy are designed to adjust the advance according to the vacuum and RPM.

[930cabman]

Originally Posted by PeteKz

Only during high vacuum conditions, such as idle or cruising. As the throttle opens, vacuum decreases quickly and advance is reduced. The vacuum pod and springs in the dizzy are designed to adjust the advance according to the vacuum and RPM.

Thank you Pete