Shamelessly stolen of the Vincent Owner's Club NG!
Peter said -
" Reed vapor pressure. The days of seeing that shimmering mirage over a cup of gasoline are over. 300 million gallons of gas are lost annually to evaporation at the gas station fuel pump. To stem this, the Fed's have dictated your fuel be less "volatile" in this particular situation - at atmospheric pressure by being less inclined to atomize and turn into vapor. Not a problem for the average car on common rail EFI at injection pressures starting at 40psi and a non issue for direct injection at 2000psi plus. But a huge one for a vintage m/c owners and particular those with lower start off port velocities either due to large size relative to displacement or cam overlap. Essentially that carb tickle now turns into predominantly an unbroken trickle flowing into your combustion chamber with little/no atomization. This is especially evident at ambient temps below about
50-60F with the blends used in the south/south east US. Many a Weber carb'd 911 has become unusable and the trend now is to replace those carbs with a 40-60psi EFI individual throttle body setup.Over a year ago I started my Shadow after 33 years languishing as basket with exactly 2 kicks, not so this February. Even on a BTH, it wetted the plugs under the original start format. Have now forgone 91 plus octane for mid grade and instead of tickling the original 289's till they foam slightly from the tickle pins at the top, only look for slight moisture at the base of the jet block slot at the gland nut. "
I wonder if this is the case in the UK?
Regards,
Kim Siddorn