Re: IML: Fuel Siphoning

["mike and linda sutton" <mikanlin62@xxxxxxxxxxx>]

Today there was a post about fuel siphoning back thru the needle and seats 
after the car was shut down.  It did not mention whether is was a Holley or 
Carter carb, but since this is the Imperial list, we can presume it is an 
Imperial and probably an AFB or a Holley,  at the long shot a thermoquad. 
Before going any further, it is not my intent to start a flame war or a 
peeing match about this, and that I do in fact respect the person who made 
the post and that Im not disputing their knowledge or experience.

Having said all that, this has been cussed and discussed , peted and 
repeated many times on this list.  The general complaint is the excessive 
cranking required in some Imperials before they will start, and is generally 
attributed to lack of fuel in the float bowls.  The causes , in no 
particular order , have been attributed to heat soak after shut down causing 
fuel to boil off in the bowl,  leaks from porosity or cracks ,  and the 
difference in todays fuels versus the fuels of the past in how easily the 
evaporate.

Now, my question...HOW can fuel siphon back thru a needle and seat after 
shut down.  The needle and seat are higher than the level of fuel in the 
bowl and once the fuel pump was to stop pumping, the column of fuel 
contained in the line to the needle and into the bowl would cease to be 
filled completely full , which would not let a siphon action occur.  Also, 
the check valves in the fuel pump should stop it from flowing backwards any 
further than the pump.  I cant believe that there are that many Imperials 
running around with fuel pumps with this condition.  I have analyzed this 6 
ways to Sunday and I just cant get there from here.  This should be in the 
archives, so feel free to dispute me all you please, I just want to see an 
explanation for this phenomenon.

I know the problem is real enough, it happens on my 62 now and then.  I have 
installed opaque fuel filters in the line to the carb and watched the fuel 
in the line before.  There is always a bit of an air pocket in the filter 
when I shut the car off, but the level never drops down completely.  That in 
itself dispels the siphon theory as far as I can see

Ok, inquiring minds want to know??

Mikey
62 Crown Coupe 


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