I work on cars for a living so Im assuming this bike functions on some of the same principles with that being said. My hawk runs great under acceleration and at idle but at highway speed, say 3200-3800 RPMs, it has a stumble or slight miss/hesitation. I can make it go away if I pull the choke out or roll into the throttle a bit. The choke is what makes me think its a vacuum. The reason Im leaning toward the petcock is when I was painting the tank I had it off and leaned up against the wall and I noticed a small leak. At the time I didnt know these bikes werent gravity operated so I thought nothing of it, wish I'd known then what I know now .
Do you guys think this could be the cause of my little stumble?

 

I doubt that fuel starvation is the cause because if the carbs were starving fuel, choke or not they will fail and WOT operation will definitely suffer.
Did you happen to have a new air filter, jet kit or a perf exhaust ?? Because it seem to be needles territory, if you have a jet kit back up the needles a notch and it should fix it.
Good luck

 

I actually put a new engine on the bike (4300 miles on it) but used my old carbs with a jet kit in them already and I have Graves exhaust and I also put a new air filter on it. How much of a pain is adjusting the needles?

 

It's actually fairly easy. You have to remove the carbs and then remove the slide covers, slides, and needles. If you say it was rejetted then there should be a small C-clip on the needles. Move them one position down (towards the pointy end) and that will raise the needle, thus giving you more fuel in the midrange. There's a writeup on carb removal in the KB.

 

Ive had the carbs off before thats no problem. Thanks for the info. I will be giving this a try very soon.