Development of the booster rocket, which is powered by 27 engines, has proven to be "way harder than the team initially thought," he told the International Space Station Research and Development conference on Wednesday.
Falcon Heavy will be the most powerful rocket booster in the world, capable of delivering a 54 ton payload into orbit.
Musk said that combining three Falcon 9 rockets together had multiplied vibrations throughout the vehicle making it difficult to test without a launch.
The maiden test flight is due to take place toward the end of the year.
The billionaire added that the best way to re-invigorate public interest in space was to build a lunar colony.
SpaceX announced in February it had finalized a deal with two private citizens to be sent around the Moon in what would mark the farthest humans have ever traveled to deep space.
Fellow billionaire Jeff Bezos, the CEO of Amazon, also announced in March his intention to build lunar vehicles and habitat modules in order to establish colonies, and has submitted a collaboration proposal to NASA.
Musk, who has said he wants to send an unmanned lander to Mars by 2020, added Wednesday that any colonization efforts should rely as much as possible on resources available on the planet.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)