slippery shopping!

[Keith Bennett]

Bar and I live at the top of a steep hill and are doing our best to self-isolate but every month we need to do a big Morrison's shop to stock up. With more snow forecast we thought we'd go this morning - very little snow around but boy, very slippery under foot and cross plies!
Gab sedately slid down Wood End but happily the main road was clear, so all good. Hardly any cars around (the downside of course is that our road is lined with dozens of parked cars cos folk seem incapable of parking on their driveways).

Haven't driven her for a few weeks and what struck me most was the small size of the pedals. You'd think after 55 year's ownership I'd be used to them by now...

Safely home and unloaded ready to be tucked back up in her garage.

[austina40sam]

Yes Keith, I thought you would have been used to Gabs pedals by now!
Oddly enough I only thought of you both this morning as I know you use Gab in the snow. Glad she is running well and no carb icing! Hope you are both keeping well Keith

[Keith Bennett]

The really weird thing about the dreaded carb icing is that Gab's perfectly happy in freezing cold dry weather, but even on a mild spring day, if a cold shower of rain comes down, so does the icing.

[austina40sam]

How odd. You would think in really cold weather like today then that is when you would get carb icing!

[Keith Bennett]

Perhaps it's mainly the Zenith downdraught carbs' design that encourages this problem. All I know is that on a really cold day, or a really wet one, Gab runs really well. But hit a heavy rain shower in spring or autumn and the old bugger begins shuddering and losing power. Luckily, with a mobile phone, I can now simply sit where she stops and pretend being on a call until the engine's heat thaws the carb out!

[Mike Hodgson]

I thought you had the later Mk1 air filter to cure icing problems.Most important the tube is positioned over the exhaust manifold (winter position).

[monty]

For nerds like me ,trying to understand these odd behaviours is fascinating. Particularly since they occur under a limited range of conditions. Personally I have only had 2 carb icing events. For icing to happen there must be sufficient moisture in the air to provide the ice. %moisture and % humidity are not the same thing. As the air temperature drops so does its ability to carry water, high % humidity at low temperature gives a low % moisture. Heat take up and transfer through the air is largely due to % moisture not% humidity. So at low air temperature with low air% moisture the air finds it difficult to remove heat from the carb or to provide the water for icing.
Remember also that finely atomised fuel in air will evaporate and in doing so will take heat out of the carb. As heat is removed from the carb ,the carb cools the contacting air and can cause condensation and freezing of water in the air giving carb icing.
After a few days at near zero centigrade there will be so little % water in the air that carb icing is very unlikely.

The other end of the behaviour scale is when high %humidity or% moisture cause the engine to run better, smoother or more powerfully. At high humidity the water vapour inducted into the cylinder becomes super heat steam so the piston is driven by both steam and expanding fuel exhaust. But the initial water vapour in the air has a volume which reduces the volume of dry air inducted and consequently reduces some the fuels contribution to power.

The really interesting case when the water in the air is mostly in droplet form such as a sudden shower or heavy rain. In this case the water has little effect on dry air volume, so does not detract from power due to combustion and since water droplets have low volume to mass ratio the steam power effect is increased.

[scotty]

Beautifully put Monty. There you have your answer KB. Simply, it all depends on the humidity level and a thing called the Dew Point, as to the effect caused when the cold draft of air and enough water combine, things change dramatically.

[Keith Bennett]

Thanks Mike, Monte and Scotty for the explanation. I never knew that adding water to fuel would actually increase its efficiency... And I have to admit that although Gab does indeed have the air box with a snout, it never used to be positioned directly above the manifold, just pointed downwards to one side. Needless to say, it is now !

[Stoney13]

think its a case of big feet really, small pedals , and some race cars use water induction to cool the fuel as colder fuel makes for a bigger burn more power