Re: Carb cleaning tip, what not to do

[Keith0alan@aol.com]

Well since I'm a testing kind of guy I decided to experiment a little. I 
pulled 6 dome/piston pairs from carbs I've recently done. The dome to piston 
clearances were all between 1.5 and 3 thousanths of an inch. Pretty tight 
tolerances. Then I took the springs out and plugged the holes in the pistons. 
Turning 
them upside down and dropping the pistons in they took between 2 and 6 seconds 
to leak down. Not as consistant as I was expecting. Then I tried something, I 
wet the piston edge with silicone spray. One thing you will notice when you 
pull your domes is that the piston edge is wet with oil or gas. With the piston 
edges wet the pistons did not leak down at all. One thing I noticed was the 
grooves on the outside of the piston. This is a technique used on some small 
engines. The grooves hold oil that acts as a piston ring sealing the space 
between the piston and wall with very little friction. I dragged out the piston 
and 
dome tht hat been sandpapered. It took about a second to leak down dry and 
about two seconds wet. The piston to dome clearance was about 6 thousanths.

       I can't say for sure that pistons and domes were matched at the 
factory but the tolerances are awfully tight. I can say for sure that this 
piston 
and dome were ruined by being sanded. 

keith williams