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CARBURETTOR DCNF THROTTLE BODIES WON'T CLOSE

Problem - I have a problem with my carbs. I have overhauled them by replacing the gaskets, the bearings etc. Now the throttles do not close smoothly by the force of the throttle spring once I tighten the 2 screws that hold the plate on the shaft. I thought that the round plate is not in the perfect place and that this is the problem, but then I found out that even if I remove the brass throttle plate and just tighten the 2 screws that hold the plate on the shaft without the plate, the shaft stops moving smoothly. It seems that the screw is bending the shaft somehow. What is wrong here? Any idea? I tried to insert a very thin sheet of metal and then it worked fine.
Possibility 1 - If you replaced the ball bearings on the shaft, you need to make sure they are seated correctly or they will bend the shaft. With the throttle plates mounted, if the mounting screw is too tight, it will warp the shaft and bend. Once you have isolated the problem, it is best to use a Henkel/Loctite product to hold the screw (instead of high torque on the screw), so that the screw is not introducing pressure on the shaft.

Problem - The bearings are new and seat perfectly. The shaft moves fines and snaps back into position without any problem, until I tighten the screws. Now I try loctite. It is very tricky because I need to have enough pressure to hold the plates in place. I have decided to change the springs to new ones. These might help as well.

Possibility 2 - The alignment tolerance that needs to be achieved is on the order of 25microns or 1thou (inches). Do not assume the butterflies will self-align themselves and you just need to tighten up the screws. 
That is not the case unfortunately and achieving the 25 micron tolerance is not a trivial task. Beryllium-copper 3mm wide ribbon is the right thickness for alignment. The butterfly when closed gently either captures the shim or it doesn't when you gently tug on the shim to pull it out. When you have it so the shim gets caught at all six locations, only then do you have the butterfly positioned correctly. At either end of the major axis and 30 degrees to either side.

Possibility 3 - Rebuilding webers without throttle shaft bearing replacement is pretty straight forward. However, throttle shaft bearing replacement is a work of finesse and experience. There are multiple ways to screw it up and only 1 or 2 ways to get it correct. It can directly affect the way the car runs and your ability to correctly synch the carbs. Those tolerances are critical. I just sent all 4 of my Webers to Jim Inglese in Florida for restoration. They came back looking brand new and with perfect function. It cost about $1600 plus tax for all 4. I am installing them this weekend. I have had vacuum leak problems for a long time. He found a broken bearing that I had never discovered. It was money very well spent in my opinion. The carbs look like they came new from Weber and function as smoothly . This guy really knows his stuff. Good luck. At the least, I would send them out to someone who is really an expert to set up the throttle plates correctly. You might have even inadvertently bent a shaft removing the screws.

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  • Urus
  • Huracan
  • Aventador
  • Gallardo
  • Murcielago
  • Diablo
  • LM002
  • Jalpa/Silh.
  • Countach
  • URRACO
  • JARAMA
  • ISLERO
  • Espada
  • MIURA
  • 350 400 GT