Scotland will move top of Group 10 if they win in Lovech, although current leaders Holland face Luxembourg the following night.
The game comes three weeks after the Scottish Premier League season ended and in the wake of the senior team's 5-1 thrashing by the United States after a week of training in Florida.
Scotland manager Craig Levein felt the Americans were more up for the game than his players but Stark has no fears that his team will switch off mentally.
"I can understand that but ours is a championship game and we need to find that edge," Stark said.
"With the group of players we have, I don't have any doubts about that at all.
"They are hungry to succeed. You need to have ability and show it in games but that resilience and hunger to do well in every game is there.
"But it's a fair point that when it's championship games you find a wee extra edge. Even allowing for the time of season then I still think our boys should find it okay."
Stark added: "We lost to Italy in a friendly. Friendly games are about honing your team for competitive games and, if you look at it, our record in championship games is pretty good.
"We are unbeaten so far and would like to come out of Bulgaria with that intact."
Stark managed to provide his players with 60 minutes of action against senior players on a Scottish Football Association training course last week while some members of the squad have had more high-profile encounters recently.
Huddersfield striker Jordan Rhodes helped his side into the npower Championship in a Wembley sudden-death penalty shootout victory over Sheffield United on Saturday, with Scotland Under-21 team-mate and Bolton striker Michael O'Halloran on the losing side.
Another player with a taxing schedule was Dundee United striker Johnny Russell, who was with Levein's squad in Florida.
Stark said: "We're at the stage of the season where some boys last played a competitive game a month ago, and Jordan Rhodes played as recently as Saturday.
"We had a few days together last week and that was really beneficial. The way they have gone about training, we are really delighted.
"We are looking at individuals and what state they are in before formulating a starting 11.
"Jordan has had a phenomenal season in terms of goalscoring and individual performances but him more than anybody would enjoy the team achievement more than anything. So I think he'll be on a big high.
"As is Johnny Russell - he's tired but he's high. He's had his first involvement with the big team, which is great.
"We have until Thursday to recuperate him from the travel but we have had the benefit from Johnny training with the big squad.
"He's an exuberant boy who shows great enthusiasm and vitality in terms of training and playing."
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