Racing on the final day of the Festival of Motorcycling is due to get underway at 12.10pm (30 August).
Roads closed at 9.30am but the first event of today's Manx Grand Prix action, the combined supertwin/lightweight race, was delayed several times because of mist on the mountain.
Riders were told to return to the paddock and prepare to line up with half an hour's notice.
Race organisers then announced a 12 noon start time - though they warned about poor visibility in places.
But more problems with fog and mist meant another ten-minute delay.
The delay will have a knock-on effect on the showpiece MGP Senior race, which was scheduled to start at 1.15pm.
Roads are due to reopen no later than 9pm.
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