If I understand you right, one guy bought a quick turn throttle from Murray and it solved the same problem you have. The bike I'm rebuilding came with a set of Murrays. I sent them back to him for servicing and also told him I was 1300 feet higher than what it was jetted for. He rejetted them and also told me that I had the old style intakes and offered to sell me the new style at a cheap price. Very happy with his customer service.My problem is, I am getting 22-30 mpgs. I found that I am getting ~90 compression on all cylinders so that may change it on the rebuild. My other problem that a lot of people have been having is that when I give it an 1/8th or 1/4 slow throttle, the RPMs will stick around ~4k RPMs. I can try to snap the throttle to try to make it idle right but turning off the engine and turning it on is much easier.
The people with my problem have been using two springs to remedy it but makes the throttle stupidly stiff. They have verified my cable routing and have sent me an extra spring that I cut 3 loops off. Supposedly, I can revert back later and it will work but after 500 miles it still hasn't worked. This is supposed to be my long distance comfortable bike but hurts my calluses after 1 hours.
After my rebuild, I will probably go back to stock carbs and try some pod jetting setups that have been floating around in this forum.
I will admit i have no experience with SpeedMotorCo´s manifold but just looking at it it looks like trash to be honest, it is jsut three cut tubes welded together and that makes for very sharp corners in the manifold which will definetly cause a lot of turbulance, good for torque, but horrible for anything else, might be ok on some low revving bikes but on the higher revvong ones like the dohc i´m GUESSING that they wont be too fuel efficient or powerfull as stock.I agree... 100% unless I'm missing something so obvious I'm not seeing it. Ive got another post about advance timing I'm working on. Ignition has been upgraded except the pickups and it idles great just above idle and loaded it breaks up and runs horrible. Brett advised 2 steps lean so that's where I'm at. Plugs say extremely rich so it makes sense to me.
I'm done with my issues here. The carb setup has fairly good reviews in my opinion and HAS been running great compared to the CV carbs. I would say that SpeedMotorCo is much more pleasant to deal with over Murray. Same setup. Different vendor