Yes my Jato 3.3 didn't respond to anything like you are saying, i'd trim the idle to make it run but when i hit the throttle she was done.
Where the HSn is there is two washers that are actually seals that were not sealing, i tried new one but that didn't work either. So i just took them out and put two small o-rings in there place and that took care of it. Sound like you have a air leak somewhere. Take off all your fuel lines and check good. Take your carb off and totally disasemble it to check o-rings. I took mine apart and put back together like 5 times to find my problem. Basically check everything that is suppose to seal that might not be sealed.