black spark plug

[charvey]

Hi all, Pottered down to Oxford on Friday nice run out about 150 miles there and back, The VH 1939 run well but a bit fluffy in the middle range when nipping between car when they were stuck in traffic.
When I got back there seemed to be a very black sooty exhaust tail end and the plug was very sooty I usually travel at about 55-60mph and it was fine then.
I do run the bike with only 5% the best grade and add some millers for the valve seat it was a rather hot day but it has never fouled the plug like that before is it to do with the heat of the day and this new fuel?
Has anybody had the same problem and it was fine on tickover and pickup. Regards Clive.

[Bernie Blundell]

Yep, most probably metrological influence, when air temperature increases, with air pressure constant, air density decreases, which will give you a richer air/fuel ratio, will certainly give dry soot on sparkplug, not sure on exhaust though.

[charvey]

Thanks Bernie, thanks for that, I am in the process of removing and checking carb just to be on the safe side and make sure nothing is amiss, Clive.