Installing Weber Carbs

[don hopkins]

What is the procedure for replacing CIS fuel injection on my 1981 SC with Weber 40 IDA carbs? Is it something I can do myself?

[Steve@Rennsport]

Hi Don:

Depending on your mechanical abilities, this is an easy swap.

The proper PMO kit will contain everything you need to do this and all you'll need are some hand tools, a Syncrometer, and some patience.

[don hopkins]

Hi Steve:
I am not using PMOs. I bought actual Weber 40 IDA carbs on eBay someone took off a 1980 SC. I know I need to use a recurved distributor. I thought I would buy that from Motor Meister. So i would need to do the timing.
So I guess I would just rip everything out. Put in a new fuel line. Hook up new linkage. And then make the proper adjustments and then just hope the whole thing doesn't explode.

Don

[Evans, Marv]

Don:
I don't think Steve was referring to PMO carbs. I believe the kit he was talking about are things like a fuel pressure regulator/meter, connector hoses, intake manifold insulators, etc. I don't remember all the items. Maybe you got all that with the carbs.

[Randy Webb]

How do you know the carbs are working right? Did you check the bushings?

YOu will also need to set them up for your engine and for CIS I think that will mean rel. rich jetting.

[dd74]

I've looked at this modification quite a few times for my 3.0 CIS engine. It involves not just carbs, but the correct manifold and linkage. I've seen it done to a few 3.0s, and have heard virtually no complaints, other than gas mileage went a bit south.

The jets and venturis have to be choked down quite a bit to work with the mildness of CIS pistons and cams. Inherently, one does not work optimally with the other, but it can be done.

Benefits vary. Most agree that throttle response is better. And there are reports of a 10 horsepower increase with carbs; Webers and PMOs alike.

One consideration is the carb set up is lighter than CIS, so even if there is not that much of a horsepower increase (though there probably is some increase), the modification benefits three ways:

1) Better throttle response.
2) Horsepower increase.
3) Lighter than CIS by about 10 pounds or more.

Going against the modification:

1) Potentially a lot of testing of which jets/venturis work best with your motor.
2) Gas mileage.
3) Price of mod. A full PMO kit is $3,000.

[al lkosmal]

The pmo website will have good recommendations for jetting, etc. Start there. MotorMeister is a good source of info and carb parts. If you are lucky the previous owner had them set up right. At the very least you will need the right fuel pump, fuel regulator, pressure guage, inline fuel filters and assorted plumbing. Also, you will need some test equipment, like the synchcrometer, etc. Buy Wayne Dempsey's "101 Projects for your Porsche" . It is a good source of info. I believe it's available thru the pelican website. check it out.

[don hopkins]

Also, I assume, the distributor needs to be recurved.

[Zeke]

Originally posted by don hopkins
Also, I assume, the distributor needs to be recurved.

I don't know if that is an absloute must. I think you can go ahead with the conversion and then you might want to have someone dial it in on a dyno. That would be the time to investigate the distributor changes. Don't just buy something because someone said to. Wait and see.

BTW, I am now a firm believer in dyno tuning.

[Joe Bob]

Originally posted by Zeke

BTW, I am now a firm believer in dyno tuning.

Ahem....

Make sure you use a LOW pressure fuel pump and DO NOT use the fuel injection one or try to regulate it down....

[si2t3m]

I have a webered 3.0L in my 914/6 conversion.

You will need insulators between the heads and the manifold. The intake port on the heads will be sealed up correctly with the insulators. If you don't use them, then manifolds won't cover the area where there is a shape for the injector in the intake port on the heads. BTW use the gasket supplied with the insulators, not the 3.0L ones.

I bored out my manifolds to size for my early 3.0L heads. As for the dizzy, call PMO. They know a place where you can get your dizzy recurved or get an early 3.0L dizzy.

The dizzy on my 78 3.0L (ROW) doesn't have the vacuum canister on it, maybe it's a dizzy from an euro model?

I'm using a Bendix fuel pump with a pressure regulator set at 3.5 psi. I'm also running an MSD box.

It sucks more gas, but when you step on it and the webers start singing there song (in my case about 2 feet behind me ) you will find that it's worth it.

Marc-André

[don hopkins]

Thanks!

[farleyd]

and the webers start singing there song (in my case about 2 feet behind me ) you will find that it's worth it.

Well, i am usually more than 2 feet behind Marc-André's car, and frankly, with its near-to-nothing exhaust - read loud, we dont hear much of the Webers whissles..... But its prolly because my own car is noisy too....

[yelcab1]

Originally posted by si2t3m

It sucks more gas, but when you step on it and the webers start singing there song (in my case about 2 feet behind me ) you will find that it's worth it.

Marc-André

If you like that, try it on 4 doubble barrel down-draft webers, on a Ferrari.

[Randy Webb]

farleyd -- the induction howl is heard more by the driver of the same car -- and is awesome.

[don hopkins]

Where can one buy intake manifold insulators?

[RoninLB]

Originally posted by don hopkins
Where can one buy intake manifold insulators?

Pelican Parts

[Tyson Schmidt]

Originally posted by mikez
Ahem....

Make sure you use a LOW pressure fuel pump and DO NOT use the fuel injection one or try to regulate it down....

Actually, there's nothing wrong with using a CIS pump with Webers, but it is essential that you use it in a recirculatory manner, and pinch the return line to yield 3.5 PSI or thereabouts.

[don hopkins]

Someone just told me that intake manifold insulators are just for early engines and not for an 1981 SC 3.0L. Is the correct? If so, then I just have to decide if the used Webers I bought on eBay need to be rebuilt and then get a fuel regulator and then I'm set to install them using gaskets.

[Randy Webb]

Tyson how do you set it up or modify it for use in a "recirculatory manner."? What hose runs where to recirc.? What other items do you need besides the pump & hoses - a holding canister?