unset($portfolio_args['ai1ec_events']);

function events_only_in_home_loop( $query ) {

 if ( is_home() && $query->is_main_query() ) // make sure to only run on home page
    $query->set( 'post_type', 'ai1ec_event' ); // select only event post type
    return $query;
 }

 add_filter( 'pre_get_posts', 'events_only_in_home_loop' );

function sort_events_in_home_loop( $query ) {

 if ( is_home() && $query->is_main_query() ) // make sure to only run on home page
    $query->set( 'orderby', 'meta_key' ); // order by a meta key
    return $query;
 }

 add_filter( 'pre_get_posts', 'sort_events_in_home_loop' );

function meta_start_in_home_loop( $query ) {

 if ( is_home() && $query->is_main_query() ) // make sure to only run on home page
    $query->set( 'key', 'start' ); // order by event start
    return $query;
 }

 add_filter( 'pre_get_posts', 'meta_start_in_home_loop' );