18-02-2021, 09:20 AM
(This post was last modified: 18-02-2021, 09:31 AM by A G Wood.
Edit Reason: Added text
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(17-02-2021, 02:42 PM)Ilmoro Wrote: The RM riley has back pressure and that isn't a modern car either....Just wondering why Austin went to the trouble and expense of providing a breather tube?
Speaking generally, any car with a sealed fuel cap will have to have some other method of fuel tank venting to avoid collapse of the tank due to the partial vacuum being formed by the fuel being drawn out of it if it is a pumped system [the humble camshaft driven mechanical pump can produce around 10" Hg 'vacuum'], or to avoid fuel stoppage in the case of gravity feed. The results of a blocked vent or the fitting of a non-vented cap where a vented one is indicated can be quite spectacular on pumped systems... When you say 'back pressure' on the RM, do you mean there is a pressure release you can hear when you remove the cap, or do you mean excessive splash back when you try to refuel? If its the latter, then apart from an excess of 90deg bends in the system, I have seen non-fuel rated hose in the filler plumbing swell up internally, sometimes down to as little 15-20mm from a nominal 50mm ID, which naturally tends to severely restrict fuel going in as well as air escaping out during the filling process.