Saturday, 28 July 2018

Carburettor Rebuild

After what I imagine is 35 years without disassembly I took the carburettors off the bike and rebuilt them. I replaced:


  • All the O-rings. 
  • The diaphragms. Both were inflexible. 
  • Cap screws. These had corroded somewhat. 
  • Vacuum Blanking screws. These were damaged from repeated removal. 
  • Throttle shafts and screws. The peening of the original screws meant that they damaged the brass threads on removal. 
  • Gaskets on cold start and float chamber. 
  • Main jet washer. These were a bit corroded. 
  • Throttle and cold start return springs. 
A few pics of this:


Before: 35 years of gunk. Note the carburettor on the left has the cold start spring replaced with a pair of other springs.


Before: The carurettor on the left, with the darkened piston, is the one with the damaged diaphragm.


Diaphragms. The one on the right is so badly damaged I'm surprised I was able to tune the bike at all. 



After: all clean, ready for reattachment. 

A few comments: 

  • One of the main jet holders was difficult to remove, there was so much gunk in it that it wore the threads down as I removed it. It reassembled okay, despite this. 
  • I couldn't adjust the idle down on the LHS carburettor far enough to be able to set the idle mixture. I removed it from the bike and reseated the throttle butterfly, being more careful this time to ensure a good seal against the throat. 
  • I had no device to remove the peening on the throttle butterfly retaining screws, and damaged the threads on the shaft when I removed them. I replaced the shafts and screws and used lock thread on reassembly. 
  • I crimped the fuel hose attached to the LHS carb on reassembly and it got no fuel. Replacing that section of hose fixed the problem. 
  • I don't have a compressor so I used a can of compressed air and a can of carburettor cleaner. 
  • I found this youtube clip from "Boxer2Valve" immensely useful: ·         https://www.youtube.com/watch?v=MpBA6wimjLc&list=PLXo0yJ7WoKfvSNxo1uZU3qupxkkf9xU4w&index=5 

  •  Probably I should've done this 20 years ago. 

The bike is running much better, it pulls better and I think that the range has increased 20%. 



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