No larger jets, try adjusting the accellerator pump arm clearance. In the gap between the pump arm and cam lever (driver's side of carb, forward of the throttle linkage) you want zero clearance. When you have the air cleaner off, and the engine stopped, work the throttle linkage. The instant the throttle moves, you should have fuel squirt out of the two nozzles in the primary throttle bore (under the choke plate) This primes the engine and compensates for the temporary lean condition from when the throttle is first opened till the fuel starts to flow from the venturis.If you ease the throttle open, the lean out doesn't occur, or isn't enough to cause it to stumble. Changing jets only changes the fuel mixture when the main metering circuit is working, that's a few milliseconds after the throttle is opened.