<VV> Carburetor mystery--Update

[Jim Becker]

I sent a reply yesterday morning.  I don't see that you have responded to 
any of my comments.  I suppose my reply got lost somehow.  Here it is again:

I don't know what the answer is.  Maybe you have already been down the path
I am about to suggest.

First off, you need to look at what common ground there is between the two
engines that could cause both to act up.  Second you need to look at what
differences there are between the stock carburetors and the modified one
that make the stock carburetors immune to the problem.  Keep in mind that a
strong shot from an accelerator pump only proves there was gas in the bowl,
not necessarily that there is enough fuel flow to keep the engine running.

The obvious common ground is the gasoline itself.  Changes could be in
composition or contamination.  Did you start using gas with ethanol?  That
could have changed by your choice or by a change in the local availability.
Did you start/stop adding some magic fuel additive?  Contamination could
have come in with a batch of gas.  It also could have been in the tank where
it wasn't causing any problem until some alcohol (whether ethanol fuel or
added drygas) or other "fuel system cleaner" picked it up and sent it to the
engine.

What can be different between the modified and stock carburetors?  When the
modified carbs were assembled (many years ago?), were now-antique parts used
that might not be compatible with ethanol?  A sticky rubber tip on a float
valve could cause problems.  Meanwhile, the stock carbs may have compatible
parts.  How about the filters in the carb inlets?  Old ones tend to slowly
loose flow capacity.  Add even a brief shot of dirty gasoline and you have
trouble.  Your water test, although valid for what it tests, does not test
flow though the filter or the needle valves.

These are just suggested places to look.  But whatever the problem is, the
source nearly has to be something common to the feeding of the modified
carburetors that the original carburetors are immune to.  Are the fuel line
connections identical with both sets of carbs or do they have to change when
you change carbs?

You may have already been down these paths.  But you didn't mention any of
them.

Jim Becker


-----Original Message----- 
From: Brian via VirtualVairs
Sent: Friday, March 20, 2020 6:38 PM
To: VirtualVairs at corvair.org ; fastvair at yahoogroups.com
Subject:  Carburetor mystery--Update

First of all I want to thank everyone who gave comments and advice the best 
I have ever seen to a question posted on the net.  I took every one of the 
suggestions very seriously and followed up on them.  Here is what I have 
found so far in no particular order.

Idle circuit-- every passage on the idle circuit was scrupulously clean I 
found absolutely no restrictions.

Venturi cluster-- all the Venturi clusters are also scrupulously cleaned and 
again no restrictions.

Idle siphon tube-- the idle cluster siphon tubes were also cleaned and again 
no restrictions.

Adding gas== it was suggested to pour gas in while the engine was running 
and see if it had any effect.  Was very difficult to do because the engine 
dies so quickly but I did try by adding gas and spraying starter fluid.  No 
effect the engine still dies very quickly regardless of throttle position.

Old gas-- this problem was replicated while the engine was on my run stand 
which has its own fuel tank to which I recently added fresh fuel.  So I 
sincerely doubt that old gas is an issue here.

Carburetor base== one of the comments said that I should check the base of 
each carburetor to be sure they were flat I did and they are perfectly flat.

Carburetor insulator and gaskets== I am using paper gaskets on both the top 
and bottom of the insulators.  The insulators and paper gaskets have been 
opened up to match the size of the carburetor.

Throttle plate-- another comment suggested being sure the throttle plates 
are completely sealing the carburetor.  I checked and they are and there is 
no leaks from the throttle shaft on the base of the carburetor.  As a 
precaution many years ago I added the rubber O-ring kit on all the throttle 
shafts.

Vacuum gauge-- it was impossible to get any kind of reading on a vacuum 
gauge because the engine dies so quickly.

Bottom line to all this I am still absolutely baffled.  I'm very thankful 
for everyone who is weighed in on this problem.  I'm hoping against hope 
that it will be some simple thing.  The fact that these carburetors worked 
for years and then suddenly didn't work with absolutely nothing being done 
to them is completely baffling.  Again many thanks to all.
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