#1 Fuel vapour Lock
Posted: Fri Apr 19, 2019 7:51 pm
S3 V12 FHC 1972 Manual. Been very hot today. After a good run the car starts and dies. Impossible to restart. Ignition electrics replaced so I'm sure it's not them. Been using the cheapest fuel which has loads of Ethanol. This boils and vaporises at about 100 deg. C. I suspect the fuel vapour locks liquid from entering the float chambers.
I did introduce a modification recently where I fitted a valve from a tee from the top fuel rail and it discharges downstream of the non return valve on the return line. Today the car misbehaved and I left the valve open for a while to vent out any vapour and introduce a cooler charge of fuel. The car eventually started. My conclusion is that the Non RV does not give enough flow to vent the system and it was not designed for that anyway, only as an overpressure device for the floats. I will now leave my new valve cracked open permanently to enables better circulation of fresh fuel. I have heard of muscle cars having a permanent 3/16" orifice on a return line to have a permanent recirculation. I could of course use premium unleaded which has no or less ethanol but who know what's in there today. I will try it next time as it's just too scary the thought of being stranded.
Any thoughts or similar experiences.
I did introduce a modification recently where I fitted a valve from a tee from the top fuel rail and it discharges downstream of the non return valve on the return line. Today the car misbehaved and I left the valve open for a while to vent out any vapour and introduce a cooler charge of fuel. The car eventually started. My conclusion is that the Non RV does not give enough flow to vent the system and it was not designed for that anyway, only as an overpressure device for the floats. I will now leave my new valve cracked open permanently to enables better circulation of fresh fuel. I have heard of muscle cars having a permanent 3/16" orifice on a return line to have a permanent recirculation. I could of course use premium unleaded which has no or less ethanol but who know what's in there today. I will try it next time as it's just too scary the thought of being stranded.
Any thoughts or similar experiences.