<VV> Carburetor mystery--Update

[Hugo Miller]

A couple of observations;
1) I never use 'starting fluid' (i.e. ether). I find that brake cleaner 
works much better - the one in the green can from Autozone - the red can 
says it's not flammable so I haven't tried that. Whenever I start and 
engine that has been standing, or one that isn't keen to fire, I give it 
a good squirt of this stuff down the air intake. It has the advantage 
that it is very volatile and quickly evaporates, so it wn't wet the 
plugs.
2) Old gas, even after it has been flshed out, can leave a really 
sticky gummy residue. I had a mechanical fuel pump on a British car with 
a glass bowl on top, which I removed to get at the disc valves. I could 
remove the discs by pressing my finger down onto them, and they would 
stick to my finger with some ferocity. The only thing I found that would 
clean it off was thinners (reducer). I should think acetone would do the 
job but we're not allowed that in the EU - too dangerous for 
health-and-safety land! Talking of which, that brake cleaner burns like 
heck if you get it on your skin. No idea what's in it but it works 
brilliantly. And I have a can of Jasco paint stripper that is so good it 
took all the anodising off my spray-gun! Predictably, the EPA has now 
banned the essential componenent (di-hexa-something-or-other. Or was it 
di-methyl chromate?). Jasco still make a paint stripper but I've no idea 
if it works. The paint stripper we get in the uk is completley useless. 
Anyway I'm rambling again.
The problem with this carb set-up seems to be that it worked perfectly 
until it was left standing for a while, then it didn't work at all. That 
all points to deterioration of the fuel, which may have left a residue 
behind somewhere. I wouldn't like to speculate where though, so my 
suggestion is probably of limited use.
Have you tried a stock carb on one side and a modified one on the other 
to see what happens? Clearly it's not leaking throttle spindles or base 
flange, as carbs will run quite well with those faults, maybe less so on 
idle. But yours dies altogether, right?


On 2020-03-20 23:38, Brian via VirtualVairs wrote:
> 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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