Sounds like you need to fatten up the pilot jet.. Those butterfly carbs are kinda finicky. Unlike a slide valve carb, you need enough pilot jet to make the transition to mid throttle position. Try a #85 pilot first. If it gets better, play with the air screw a little. I think stock setting is 2 turns out on the SS, so try that. if you need to go more than 2 turns out, you need to go fatter, like say the 92. My SRV is at about 1.5 turns out.