<VV> Carb break down and diagnosis

Tony Underwood tony.underwood at cox.net
Sun Oct 18 16:53:21 EDT 2009

At 01:41 PM 10/18/2009, Stephen Upham wrote:
>Actually, the more I look at the idle circuit tube, the more I'm
>convinced that a) there never was an obstruction or b) that I have
>removed the obstruction without actually seeing it.
>I have been able to see a good deal of light though the tube since
>its removal.  This was the first test that I performed.  The beam of
>light at the end of the tube appears to be nice and circular.  There
>is absolutely no visible debris in the tube.  I'm seriously
>considering putting it back together and see what happens.

Before you do, don't forget to check out that other part of the idle 
circuit that runs through the carb body down to the mixture screw and 
the discharge port.   The air bleed is only a part of it.   There's 
more plumbing down below.   That's the area that usually ends up with 
debris stuck in it since fuel flows through it, while the venturi 
cluster air bleeds only pass just that, air.

If you have a piece of trash stuck in that idle mixture passage 
somewhere, fixing or even replacing the venturi cluster still won't 
help you.   Blast come carb cleaner through those idle mixture 
passages and make really sure they're clear of anything that could 
restrict flow through them.    If it were me, that's where I'd be 
looking for what's been troubling you.

I've had luck blowing carb cleaner through the idle mixture screw 
hole while blocking the discharge ports in the venturi with a finger, 
to force cleaner backwards through the passages and blow it all out 
through the jet and cluster plumbing.


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