Forum - Briggs & Stratton Racing
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gary edgar

Registered: 06/06
Posts: 3
Reply with quote  #1 
When viewing the Walbro PZ26 on the World Formula from the front, on the opposite side to the idle screw there's a small "vent". Nobody here in Australia seems to know what it's purpose is. Can someone enlighten me?
I was once accused of spraying fuel on a following kart and one WF owner suggested that it probably came from this "vent" under extreme cornering and that the fix was to run a tube from it to the chassis so any vented fuel would hit the track and basically evaporate. I did so and it seems to have worked, but I would still like to know the purpose of that vent.

Registered: 06/22/11
Posts: 188
Reply with quote  #2 
CHEATER!!!!  lol

There are two vents on the carburetor.  The bowl vent that runs out of the bottom of the fuel bowl that prevents the fuel level in the bowl from exceeding a critical level.  It works as most bathroom sink emergency by-passes, if someone forgets to turn the sink off it doesn't spill and flood your bathroom.

The second vent is an atmosphere vent.  It equalizes the pressure within the carburetor to that of the air around you.  Negative or positive pressure in extreme cases would either prevent fuel or push too much fuel into the system causing your engine not to function correctly.  I would caution you to make sure you are NOT shutting off this vent.  It will likely impact engine performance and/or push fuel out your bowl vent as the pressure HAS to go somewhere.

I would suggest lowering your float level as this is helping fuel migration.  Correct this and there should be no need to take other actions.

gary edgar

Registered: 06/06
Posts: 3
Reply with quote  #3 
Many thanks Briggs! Accurate WF knowledge can sometimes be hard to come by Down Under and I'd drawn a blank on this one. Your explanation of the atmos vent function clears that up and also suggests to me why that on a couple of occasions when track direction has been reversed, that on two different racks in a single hairpin in each instance, I experienced what I can only describe as "fuel starvation" causing the engine to miss (even stall) then recover after a dozen or so metres. I'll do as you suggest and remove the tube I'd attached to that vent and if needs be alter my float level.
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