Checking Carb Floats for Cracks PDF Print E-mail
Written by BMWVMCA NEWS   
Wednesday, 06 August 2008

Checking Carb Floats for Cracks

Many moons ago I was in the process of reassembling my first vintage BMW motor. It had been recently rebuilt from the bottom up and I foolishly presumed once assembled it would be no great feat to start and tune it to it’s former glory.

I immediately found otherwise. In spite of meticulous valve setting, timing and carb setting I could start the bike (with some difficulty) but it would not run for long without immediately fouling plugs. At my wits end I made the call to Vintage BMW Mecca- Sturgis, Mississippi.   In speaking with Vech he suggested replacement of the carb floats. In my ignorance I was hesitant to do so without being able verify that the floats were, indeed, bad.   What could possibly go wrong with something as simple as a brass carb float ??? 

Several days later the new floats came and were installed. Amazing !!!  All tuning problems resolved.  It seems these floats are notorious for developing cracks allowing the entry of gasoline and altering their height and operation.  What amazed me even further is that I still could not see evidence of a crack in the old float even though that was obviously the problem.  I now carry a spare float carefully wrapped in foam in my tool kit.

I recently came upon a method of checking floats for cracks which I hope will be helpful to others.  Place the float in your refrigerator freezer for an hour. Fill a small container with hot water, submerge the float and look for a small stream of bubbles. The hot water will heat the air inside the float causing it to expand and exit the crack, if there is one.

Credit for this idea goes to Roger Long of the AMCA. 

Larry Hassard

Last Updated ( Monday, 08 June 2009 )
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