I have this same engine and I have never had any trouble like this. It was as you said very stiff until it was broke in, but after the break end period about 6 tanks it now runs with the best of them. I did have trouble with an older tigershark 46 red head engine when I first got it. I could not get it to idle at all. Not matter what I did it kept loading up before I could get into the air. I called Tigershark because it was still under warranty and they just sent me another carb. That fixed the problem and it has been a great engine since then.. That was two years ago. Since then I have bought 2 more Tigershark engines (52 & 46) and both are great running engines.
The warranty on these engines is two years. If it is still under warranty try talking to your Tigershark dealer.
Thanks