Weber vac line, one carb or two?

[Jub]

Hi all,

I have been sorting out some issues with my rough idle, and noticed something strange. On one of my merc 250's, the vac line from distributor goes to only one carb (the other carbs inlet nipple is closed off with a rubber stopper), and the other 250 has the vac line connected to both carbs?

Any thoughts (what are you guys using, one or two)?

Jub

[Jub]

Exactly like this(notice vac line to first carb, second carb vac line plugged; n10's hook up is this way):

benz1_zps420d01db.jpg Photo by n8tabasco | Photobucket

[n10]

Wow that's creepy...my whole Photobucket right there.

Oh wait...just the pic. My PC was logged in so it went to my bucket.


Hey Jub,
I cant remember why the install instructions told me to do that but it seems to be all good. I think its because the Weber doesn't have the vac activated diaphragm like the Zeniths (?)

[mosu]

If the vacuum line connects to the distributor advance, you can just connect it to one of the carbs on a ported nipple (no vacuum at closed throttle, vacuum at any other position).

[Jub]

Hi Mosu,

Never really understood how vac plays in carb, just know that when it leaks it will not hold idle. The 250 that has vac hooked up to a single carb works great (even better than the one hooked up to 2 ports). I am wondering if one is actually better overall. The reason I say this is because my 250 hooked up to 2 ports always took time to crank up (even after new coils/wires/copper plugs/pertronix ignition/battery, etc.). Someone once PM'd me to check vac pressure...but never really followed up. I did notice that the vac diaphram hooked up to my diz is MASSIVE (never seen another like it). Maybe between the larger diaphram and the one vac line set up, the car starts up on a twitch of the key...don't know?

[Jub]

Here's my vac (hooked up to diz). It's a whopper. Kind of hard to tell on photo, but it's almost size of Diz cap