R100GS: Redneck Manometer

      So, you need to balance those Bings.

But you're as tight as a duck's arse so you're not going to buy a proper carb balancer, and you can't quite be bothered learning to do it all by the rattling of the gearbox either?

Well, what you need is a Redneck Manometer.


  • 5 meters clear vinyl 5mm ID pipe.
  • 1 meter wooden plank, or similar.
  • Some of those little staple things meant for electrical flex.
  • About 20cc of heavy motor oil, preferably colourful stuff.
If that costs you more than $10, you're shopping in the wrong place.


  1. Make a U-shaped loop of pipe the length of the plank, with two even-length ends ends left over.
  2. Staple the loop in place on the plank without kinking it.
  3. Hold the U vertical, and draw up (or if you have a tiny enough funnel, pour in) enough motor oil to fill both sides of the U to about half way up the plank. Which should work out to about 20cc.
  4. Allow oil to settle and bubbles to escape.
  5. Label the left end of the pipe 'L' and the right end of the pipe 'R'. This will save confusion later.


  1. Warm up engine well (eg: go to shops and buy beer. If shops too close, go to brewery).
  2. Prop or hang the manometer vertically somewhere near the bike.
  3. Attach the L end of the pipe to the left carb's vacuum port.
  4. Attach the R end of the pipe to the right carb's vacuum port.
  5. Start the engine and watch the oil bounce up and down! If it bounces too much, use heavier oil. If it's too sluggish to respond, move somewhere warmer. Whichever side is higher (on average) has more vacuum.
  6. Back off throttle cable adjusters so that throttle cables are loose with throttle released.
  7. Adjust idle to 1000rpm and idle balance so that vacuum is equal. (adjust with screws on linkage on inside, near front of carb)
  8. Adjust idle mixture (see Snowbum's page, linked above) if necessary.
  9. Adjust throttle cables so that the vacuum remains equal when throttle is operated.
  10. Shut off engine BEFORE removing pipes. Do not remove pipes while engine is running, or the unbalanced vacuum will pull all the oil out of the manometer and into the engine, which will foul your plugs and piss off your neighbours. Don't forget to put the vacuum port screws back in.

Care and Maintenance:

  • Hang on a hook so you don't knock it over.
  • Those beers still cold?

Bonus R100GS Throttle Cable Fix

I also managed to fix the cracked ends of the throttle cable outers, and thus make carb balancing possible, by gluing aluminium tubes over the ends. See above, under "If you're as tight as a duck's arse ...". Works pretty well, and I reckon it might be worth threading heavy springs onto the ends of brand new cables to prevent them cracking in the first place.

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