<VV> Carburetor Mystery

[Hugo Miller]

I doubt I am going to suggest anything that you haven't already 
covered, but this does sound like old gasoline gumming up the works. One 
would presume that carburettor cleaner would dissolve the glue-like 
residue, but does it? I have found that thinners (reducer) will shift 
it. If it were mine I would strip each carb down and soak each part in 
thinners. Other than that, it is indeed a puzzle. I would also eliminate 
the entire fuel system by rigging up a syphon feed from a can into the 
carbs.

On 2020-03-19 15:14, Brian via VirtualVairs wrote:
> Over the years while working on Corvairs I've encountered a lot of
> mysterious things.  But in every case the mystery was ultimately
> solved.  Solved either by extensive research into shop manuals, input
> from other Corvair guys, or just plain figuring it out by myself over
> time.  However, now I've got a mystery  that may be unsolvable.  I'm
> sure hoping it's not but I am baffled.
> Here's the setup.  I have two engines I use in my track car.  The
> first is a176 cubic inch one using 3 9/16 pistons.  The reciprocating
> assembly is balanced and it has hot cam.  The second one is  3.1 
> liter
> using Volkswagen Porsche pistons and cylinders.  Like the first
> engine, everything is balanced and it has a cam.  Each engine has its
> own ignition system.  The only common item to both engines are the
> modified Rochester carburetors.  The Venturi has been poured out to 
> an
> inch and a half and the Venturi cluster arms extended to gain the
> correct distance from the Venturi walls.  These carburetors have
> worked for many years on both engines.
> Last summer something mysterious happened.  Neither engine would
> easily start and when they were finally running they would only run
> for a couple of seconds and then die as if they were out of gas.  
> This
> was regardless of the throttle position.  After the engines would 
> die,
> operating the throttle shaft would result in for very strong
> accelerator pump shots so it was obvious there was gas in the
> carburetors.  Nothing I did would correct the problem.  Hours and
> hours went by with no success.
> Recently I tried again.  This time using the run stand my club built.
> This made it much easier.  I didn't have to swap engines in and out
> of the track car.  Using the1 76 in.³ engine, I first installed four
> stock carburetors.  The engine started and ran perfectly responding
> correctly the throttle position.  I then installed the modified
> carburetors and got the same results as last year.  Hard starting and
> only running for a few seconds before dying as if out ofa gas.  I 
> took
> the carburetors off and made sure every passage was clear and the 
> fuel
> bowls were full.  I even tried different main Jets sizes although I
> had very little hope that that would affect anything.
> After checking each one of the carburetors I put them back on the
> engine and experienced the same old results.  This is a mystery that 
> I
> cannot fathom.  Why suddenly after years of working perfectly did
> these carburetors now refuse to work?  I should mention that while I
> had each carburetor apart I filled the bowl with water and using my
> air supply blew air down through the Venturi with the throttle plate
> open.  In all four cases I did get a fine mist of water on my hand
> which I was holding on to the throttle plate.
> What a mystery !  Why did these carburetors suddenly not work?  Why
> when all the passages a clear and I can get water to spray on my hand
> as if the carburetors were on the engine why do they not work when
> installed  on the engine?  Absolutely nothing was changed on the
> engine between the runs made with stock carburetors and the attempts
> to use the modified carburetors.
> To say I am baffled is an understatement.  Does anyone have any 
> ideas?
>
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