With 22r Weber conversions, the main/port advance (the "front" port on the distributor advance module) is always connected to port vacuum at the carburetor itself.

However, not all conversions treat the sub/idle advance (the rear port) the same way. In most of the swaps I see, including those in LCE instructional videos, this port is simply capped off.

BUT, there are instances like this write-up, where this rear port is connected to manifold vacuum:

http://www.lcengineering.com/LCNewsl..._TECHNOTE.html

What are the differences/advantages of either set-up?

 

Consensus seems to be that the rear port of the distributor module retards timing at idle for a more complete burn and thus cleaner tailpipe emissions.

If that's true, someone needs to tell that to my truck. It idles like dog˟˟˟˟ and smokes like crazy with that rear port connected with either the stock Aisan or the new Weber carburetor.

And not only does the truck run better with that rear port disconnected, it runs better with that vacuum line left open to atmosphere. If I put my thumb over the end of the line, it runs like crap again, as if the new Weber isn't letting the engine breathe. I'm not a master tuner, but that indicates to me an overly rich fuel mixture... but I have it set as lean as I can go, and most argue that the jets in these carbs are too lean from the factory. Most guys go richer, not leaner. I'm only 700 feet above sea level.

 

I have a 1984 , 22r in my truck. Has a weber carb, starts well, idles well, does not hesitate on acceleration. I purchased this truck recently and I have not had a chance to drive it out on the highway. I noticed the distributor two port vacuum advance has both the ports together with the hose, no connection to the carb or anything else. I tested both vacuum advance ports with the mighty vac and neither one work. Should I leave well enough alone? If I go for a new vacuum advance, I would like to try the single port unit, but am having a hard time finding a new one. Any advice would be appreciated.

 

Triple, I literally just finished installing a Weber 32/36 from LC Engineering and I couldn't get it to tune for schizzle. I finally decided to check my timing and I had it set to 5deg with the stock carb. Well, when I hooked up my light it showed that the timing was retarded WELL past 0 and I also realized that I had forgotten to hook up the vacuum advance to it. I reset it to 5deg and hooked up the vac adv. and now she runs like a top! I inherited this truck from my Grandfather and it had sat for several years with nothing done to it. I could not get the stock carb to work after a rebuild and I had also bought (read WASTED $$) a cheap new carb from Amazon. Long story short - I am soooooooo glad I put this Weber on and it runs like CRAP without the vacuum advance hooked up. Also, like you said earlier, I have to leave the rear port disconnected and open or else it won't run well at all. Now, I'm not a huge carb guy either, but I can't see how this would indicate being too rich. I don't notice a heavy gasoline smell from my exhaust like I used to and I made VERY sure that I re-tuned the Weber just like the instructions said after I reset my timing so I think I'm on the right track. I'll have to drive it more to see if I have to keep readjusting but I think I'm good with my vacuum advance hooked up as it is. Oh, and I used the open port on the base of the carb passenger side as that's the one they said was for the vac advance.