Weber carb question on correct mounting of carbs

[Tony]

I did a basic rebuild on my two carbs, mounted them with new O-rings, tuned them and they ran fine. Plugs looked good. Now I am noticing occasional snapping at low rpm/idle. Went to retune and noticed that pressing down or pulling up on the carbs changes the rpm. (One acts one way, the other is the opposite) Before I tune, I want to tighten them correctly. I assume that having them correctly sealed/mounted would be a prerequisite to being able to correctly adjust the idle mixtures. Question. When the rpm increases, does that indicate an air leak or a proper seal? I am not sure if I need to tighten the top nuts or bottom nuts. I used a flow meter to balance the carbs and they are very close, but it is difficult to adjust the idle mixture, one barrel at a time, by listening to rpm changes. Hope the correct tightening of the carb mounts will make the adjustment easier.

 

Any suggestions or insights would be appreciated.

 

Thanks,

 

Tony

 

1993 Supersprint

[Zona]

The problem is you didn't fix the idle mixture properly so it will need to fix and correctly adjusted. Make sure to tighten the top nut it will help in proper balance of carbs.

[TheDingo8MyBaby]

I'm not sure that it's quite that easy.

 

There are a number of things that it could be, but to ensure a good seal, I'd suggest spraying starting fluid near the seal to identify what cylinder the leak is occuring in.

 

Have you made sure your thackeray washers are set with the appropriate tension? Another thing to note is that webers are generally mounted as a cantilever beam, but to add stability, a brace running to the outer end of the webers will do wonders as shown in this diagram.

http://i.imgur.com/XjQfIYs.jpg

 

Once you get a good seal, then I would adjust the idle mixture. The best process for setting the mixture is to use a wideband O2 sensor. I have yet to find any other process that gets you anywhere close.

Edited May 5, 2015 by TheDingo8MyBaby