Malcolm Cox wrote:
>
> I have a 1622 MGA, with a pair of 1.75" HS6 SU (originally from a Volvo
> I believe). Perhaps this problem will strike a chord with someones
> experience.
>
> The problem is that when the engine is switched off, if the float
> chambers have not been first dried out by idling with fuel pump off, it
> will not immediately restart unless a carburettor slide is first
> manually lifted. If left (wet) for 20-30 minutes it restarts easily.
> This pattern is valid at any engine temp from dead cold to screaming
> hot.
>
> Either drying out carbs or lifting slide is inconvenient. The need to
> occasionally manually lift the slide prevents me from fitting air
> filters which I really want to do.
>
> On an earlier strip down, (before I learned the drying out trick), at
> the point in each aluminum manifold where the downdraft becomes
> horizontal, I was amazed to find a small pool of viscous dark purple
> liquid. I believe this was "distilled" pink die from racing fuel,
> suggesting that fuel is collecting at this point in the manifold, then
> slowly drying out.
>
> Various float levels (including the correct one) have been tried with no
> effect. Fuel pressure has been fiddled with endlessley, with no
> apparent effect. I am currently running a 2.5psi Facet fuel pump with no
> improvement. This style of pump allows the line pressure to bleed back
> past the piston back into the tank when the pumpmis switched off, though
> I dont know how quickly.
>
> Since the problem occurs at any engine temp, including dead cold, fuel
> vapor lock is not an issue. These HS6 have a compliant mount of float
> chamber to carb body however I wonder whther there may be some
> "thrashing" taking place at low RPM, suffienet for the float to seal
> poorly and cause temporary, momentary flooding. (I fitted ball style
> float valve without effect)
Malcolm,
I could be way off beam here, but I think your problem
might be that the carbs are too BIG. The 1.75" HS6 is
a pretty big carb and a pair of them will very happily
feed a 3 litre engine.... let alone 1600cc.
If you went down to 1.5" you would dramatically increase
the gas speed through the venturi. I've come across
situations similar to yours and going back to the original
carbs solved the problem.
Faster air flow > better atomisation > no puddling of fuel
(which you appear to have, from the die spot you found
inside the intake manifold). Facet pumps, Grosse jets and
fuel return rails won't help. Less gas to stick things up WILL.
Give it a try. And remember, you've got to lean to be mean!
MHD
Auckland
|