Was wondewring if rthe carb needs to be pulled to remove the limiters on the H aL jets so you can adjust them? . Al
If it's like the 490/500/501 and 355t, you should be able to use a drywall screw through the adjustment holes on the plastic cover. A little fanagling and no need to pull the whole carb.
I just pulled the limiters on my 490 yesterday. They were really tight and the drywall screw just striped out the middle and put a nick in the tool surface of the H screw. Ended up pulling the carb, which was super easy to do. No boot to wiggle it out of, just sits flat on the intake, four screws, two fuel lines with no clamps, throttle and choke linkages which just slip out. Had it off, pried out limiters with detail flat-head, and re-installed in a jiffy. Used a couple of small bondhus tip Allen wrenches to plug the fuel lines. Counter-clockwise til stop is where mine lined up to remove. Maybe that's why the screw trick didn't work? As the screw tightened it turned the limiters clockwise.
Were you using a course or fine thread screw? I've done a couple 490's a 500p and a 501p and never had a problem using a course thread drywall screw. Job done in less than 5 minutes...