Thanks Gary, Keith, Bob & Alan for your responses. Here's a bit more info
after further investigation this morning: oil levels about the same in the 2
dashpots - a little low but topped up - no change. Hot cranking compressions
180, 175, 175, 180 (they're usually between 175 and 185, with only about 5psi
variation) I know it's the rear carb that's spitting as running without the
air cleaners I can see fuel mixture spitting out. No apparent vacuum leaks - I
do have a vacuum guage taking off from the sandwich plate on the rear carb,
but the line's intact and the guage working correctly. The only clear
indication of any variation between the cylinders is that no. 3 plug looks as
though that cylinder is running weaker than the rest - electrode is light grey
as opposed to brown on the others. However, I can't see how a carb issue would
cause only one cylinder to run weak. Could it be a valve clearance issue? I
checked them around 2500 miles ago.
Regards
Peter
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