Der new Webers. How should this be setup?
 

The '73 I just purchased has Weber 40 IDA conversion on a 2.4 liter that was originally CIS. The engine has been converted to S specs, except for the MFI.

The heads where represented as S heads. Sure enough they are set up for fuel injectors. Here is a picture:

http://forums.pelicanparts.com/uploads/DSC01843.JPG

The injectors have been chained together with vacuum hose, which in turn is connected to the distributer vacuum advance. It seems the injectors have not been plugged, eg. disconnecting the vacuum line creates a vacuum leak.

So the questions are:

1) Where is the distributor vacuum advance supposed to connect? Obviously not to the injectors.

2) What is the normal way to deal with the injector holes on a Weber conversion? This seems mickey mouse to me.

If I remember correctly

Whoa. That is bizarre. The last conversion I saw had metal plugs for each injector. I think this is the correct way to do it. Then you'd time the engine for 35 degrees total advance with no vacuum line connected at all since it was only there for emissions on MFI.

Hmm, not 100% sure, but I think that the MFI cars had vacuum line plugs that were located on the throttle bodies. Let me check 101...

Yup, on my 2.7 RS injection setup, there is a vacuum hose port coming from the end. So this setup would work properly if setup correctly...

-Wayne

Wayne,

So If I understand what you are saying, the MFI has connection for a vacuum line beneath the throttle plate that would be used (one of the 6 would be used) to connect the distributer advance? You are saying that since my setup is beneath the throttle body it should provide similar vacuum?

Maybe so, but there must be a proper place to connect the vacuum line on Webers. Where would that be?

Can anyone share a picture of a proper vacuum line setup on Webers?

I took a look at the spot Zendelar indicates and sure enough there is a hole on each throttle body in that location (not a tube to connect a vacuum line, a hole). These holes look as if they would open beneath the throttle butterfly. I can't fit my head in to look into the holes but they are all plugged in some way and do not leak vacuum. If that is the correct location, what is the proper way to open up the hole and connect the vacuum line?

If it complicates things more, the distributer should be the correct S MFI unit. However I haven't checked numbers to confirm this.

below throttle vacuum is the same where ever you get it from. i've never seen your version, but it would work fine, even though it looks funny. is the dist vacuum unit really an advance, or is it a retard? if the idle speeds up with the hose pulled off, it's a retard and you don't need it at all. then you could use the screw in plugs in the injector holes.

Hi Chuck,
According to the factory manual, you have either a Bosch or Marelli distributor. Assuming you have the stock distributor, both vacuum units retard the timing at idle and off idle (low speed). This is for emissions control. The timing at 6000 rpm should be adjusted with the hose disconnected.

At WOT, the manifold signal is usually lower, so the vacuum unit should not work at this time. The factory setup normally uses the manifold vacuum signal at the intake manifold, but it appears the PO used the injector ports to get the same signal. IMHO, I would get some injector plugs from PMO, lose the vacuum signal and try the timing specs for an early S engine. Retarded timing causes the engine to run hotter.

FWIW, on my '69 w/Webers, there are two vacuum ports, one on each end of the intake manifold for cylinders 2-4-6 (right bank). These ports point to the outside of the vehicle. These tee together, then it goes to a throttle compensator (only used in '69) and to the vacuum unit on the Marelli distributor which has been replaced by an early Bosch S distributor w/o vacuum.

Your 911 being a '73, there are no smog issues to deal with. :)

Hope this helps,
Sherwood
http://members.rennlist.org/911pcars

Here's how I did it.

http://forums.pelicanparts.com/uploads/jac72t1.jpg
http://forums.pelicanparts.com/uploads/jac72t2.jpg

When I converted to Webers many moons ago, I initially ignored the vacuum retard unit, and just left it disconnected. However, I couldn't get the car to idle below 1200-1500 RPM. To remedy this, I drilled just below the throttle plates, tapped and installed vacuum pick-ups. I ran the two vacuum lines from the pick-ups to a T fitting, just like the stock MFI set-up, and then ran the single vacuum line from the T fitting to the vacuum retard unit. It's worked like a champ ever since.

Sherwood - how odd - I don't think my '69T (with Webers) had any vacuum setup on the carbs and certainly had none on the (Marelli) distributor. It was an Italian market car.

I never really looked that hard...

As an aside, don't the MFI throttle bodies have some sort of balancing piping on them as well.

Cam,
I'm glad you're around to help validate my periodic lapses in reality. I checked the old Marelli and there is no vacuum unit on it (somebody stole it! naw). I was confused by the Marelli pic in the shop manual for '72 and up 2.4's which does have a vacuum retard unit.

The vacuum setup on my Webers is only for the throttle compensator which probably wasn't installed on your Italian 911. Thus, vacuum ports were probably not drilled on your manifolds either.

TBird,
Can't get it to idle below 1200 rpm unless you retard the timing? Hmmm. You should be able to kill the engine by backing off the idle speed screws. Maybe idle air screws too far out or vacuum leak somewhere?

My apologies Chuck and everyone,
Sherwood

I just got done toying with the timing and advance.

I removed the vacuum line from the distributer. It is in fact a retard mechanism.

I dialed in the full advance to 38 degrees without regard for advance at idle (manual says 5 ATDC, I'm probably 10 BTDC which makes me suspicious of the mechanical advance mechanism).

The car runs much better.

Next I will be plugging up the hoses coming off the injectors, right now they create something of a small plenum between the throats.

Sherwood
The engine would not idle below 1200-1500 with the idle stop screws turned out all the way and the vacuum retard unit disconnected and 35 degrees of advance @ 6000 RPM. This was 15 years ago, so I can't recall exactly where timing was at 1200 RPM, but it was significantly advanced. Anyway, the remedy was as shown above, i.e, I let the distributor do its work as the factory intended.