I am Bulgarian passport holder, travelling from Dubai to Kuala Lumpur (to and from) via Delhi and Mumbai with layovers of 2-4 hours. The flights are with Jet Airways and Malaysian Airlines.
Do I need an airport transit visa for India?
According to TimaticWeb:
Visa required, except for Holders of an Overseas Citizen of India Card or Booklet, or:
Visa required, except for Holders of a Person of Indian Origin (PIO) Card, or:
TWOV (Transit Without Visa): Visa required, except for Holders of confirmed onward tickets for a max. transit time of 24 hours.
Hotel facilities are available in Terminal 3 at Delhi (DEL), provided holding boarding card for connecting flight.
Therefore you won't need a transit visa since your layover is shorter than 24 hours.