I'ld check all your fuel lines first and tank first make sure there are no holes, yeah i know there brand new but check them, i had all sorts of problems with an engine because the brand new fuel tank i put in with the new engine leaked. Look for air bubble in your fuel lines. Then i'ld pull your carb a part and clean it up, check the 'o' rings etc. while your at it. Put all the needles back to factory while your at it and go from there.

When did it start playing up? as soon as you changed the tank etc, or a bit after that.

Yeah it might be the front bearing also but it would normally develop over time.