There have been lots of rumours in the UK about the great unleaded question.
Much heated debate has been had (eg. MG Owner’s Club, Jag-Lovers, etc.) even
though the US/Canadian unleaded experience has been, well, boring. It is
amazing that the wealth of unleaded experience/information here on the
western side of the pond has not been utilized in the UK or, in a number of
cases, even believed. As has been said before (see Archives: XJ, Saloons,
XK), the steel valve seats in the Jag head are compatible with the unleaded
fuel. As far as timing goes, John Horner is right - the cars run fine on
the higher octane unleaded without timing changes (my experience: '62 Mk2
3.8, '73 S1 XJ6). The cars in the UK should also do fine. If not, re-read
the last part of John H.'s post.
Dave Q.
Neuhorst, SK, Canada
From John Horner (US):
My '67 420G with the 4.2L XK engine runs at stock timing on the commonly
available high test unleaded here in the US. Don’t be so sure that you need
to retard the timing until testing. Y’all do remember how to optimize timing
by on the road pinging/pinking testing, right :)?<
From John Pickett (UK):
Rumour has it that XJ6 with alloy heads have valve seats which can take
unleaded fuel, but you will need to change the timing by about 3 Degree’s,<<