sticky/lean after torquing carb

[LOOGLE]

I tightened down (dual weber dcoe 45's) to manifold due to a slow fuel leak from in between the manifold/carb after driving. They are soft mounts I believe. I did not crank them down hard. 

 

- After tightening the balance was slightly off. 

- Idle is super lean @19/21:1 via wideband a/f gauge.

- I now have both carbs synced but it's pulling over 10 kg/h via air flow meter. I think they were closer to 5-7 when it was running well. 

- I've tried setting throttle plates in various positions over first progression hole. doesnt effect it much. 

- Idle is erratic but plates move freely. swapped out idle screw with no luck.

- Small adjustments of idle screw or blipping throttle results in racing that needs to be adjusted back down with idle screw.

 

- Motor was running great (a/f ratio, idle, driving, etc.) before I tightened down the carb bolts. I tried loosening them too with no luck.

 

I keep on testing new adjustments but I dont want to keep running it so lean. I'm suspecting a vacuum leak but all bolts seem to be tight including manifold/carb bolts obviously. 

 

Any help is appreciated! 

 

[datzenmike]

Suddenly lean means you have made a vacuum leak and air is getting in after the carburetor, making the idle mix very lean. Find and seal the leak and reset the carburetors back to where they were.

[LOOGLE]

So I ripped the whole thing apart. Smoothed it all out. new gaskets/ gasgacinch:

 

manifold - gasket - heat shield - gasket - spacer - soft mount - carbs.

 

Still had an erratic throttle and lean idle. 

 

Turned out the linkage to balance the carbs was not letting the throttle plates return to the idle circuit behind the progression holes. This was due to a channel on the back of one of the carbs (pictured below). So when I torqued down the front carb with this channel, the carbs sat uneven and it set the balance off. It would never have let both carbs return to idle together.  I've searched endlessly and I can not find a weber dcoe with this feature on it although the cap says its a true bologna weber with matching numbers.     
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I've also seen many places that the plates should completely cover the first progression hole. Not the case for me. Ran lean until I let them seat themselves. 

 

Up and running now. Just a little lean when letting off throttle which I suspect is the plates still not returning to idle circuit fast enough.  

 

As always, thanks for all the help. 

 

[Stoffregen Motorsports]

The carbs need to be balanced before you can adjust the idle mixture.

 

What kind of linkage do you have? The shaft type, on the manifold with two linkage rods, one going to each carb? Or the centerpull type with the two carb linkages joined at the middle?

[LOOGLE]

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I havent messed with the idle mixture. It was fine before I torqued the carbs down so I knew it that wasnt the problem. AF ratio is spot on 90% of the time so I'm gonna let it be for now.  

[LOOGLE]

Better pic of linkage. Maybe someday do something better when I have time to research the best set up for my application. Also can't find a "474" manifold anywhere either. 

 

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[Stoffregen Motorsports]

On 4/11/2024 at 1:50 PM, LOOGLE said:

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I havent messed with the idle mixture. It was fine before I torqued the carbs down so I knew it that wasnt the problem. AF ratio is spot on 90% of the time so I'm gonna let it be for now.  

Didn't you say it's lean now?