<VV> Float drop question

[HallGrenn at aol.com]

In a message dated 7/24/2008 9:39:01 P.M. Eastern Daylight Time,  
simpsonj at bellatlantic.net writes:

I posed  the question -- "Why is the float drop important?" -- 
yesterday because I  was helping a fellow Group Corvair member swap 
the carbs on his car to a  pair that supposedly had been 
rebuilt.  When we installed them, the  car could barely be started, 
let alone run well.  We'd bench checked  the external adjustments, but 
"assumed" the internals were ok.

In  an effort to figure out what was going wrong, I pulled the top on 
one of  the carbs and checked the float height -- both the height and 
drop were  wrong.  The float was set too high by a bit over 3/16" 
(hence it was  flooding) and the drop was 2 1/2" vs the book 1 
1/2".  I understood  the float height issue and flooding, but was 
curious as to why there was  even a spec on float drop.

(No, the rebuild was NOT done by any of the  national vendors; there 
were done locally.)

Thanks for the  responses.

Jim Simpson
Group Corvair





I went back to my carburetor books on this.  The float drop is listed  as 
important for two reasons.  First, if the float drops too far the  needle will 
become cocked and jam in an open position causing  flooding.  Because flow is 
controlled by needle movement of only a fuel  thousands of an inch in normal 
driving there is a designed limit to  movement.  Second, to limit the ultimate 
travel so the float(s) don't touch  the sides or bottom of the bowl.  Because 
the float is designed with a  certain mechanical advantage over its arc to have 
the necessary force to close  the needle in the seat it may also be that 
incorrect drop could compromise that  mechanical advantage if the drop in 
incorrect.  I also learned that  vertically oriented needle and seats like ours are 
less likely to be  contaminated by rust or dirt that could hold the needle open 
like older  horizontal needle and seats in older carb designs (the Stromberg 97 
was cited as  a classic example of this problem).
 
Bob Hall
Group Corvair
Washington DC Suburbs



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