[QUOTE=Al1943;12483668]Has nothing to do with the limit screws.
Go to
www.parktool.com for instructions for dérailleur tension and limit adjustments. Most bikes have barrel adjusters for tension adjustments.
Likely not a problem setting tension. Sounds like cable is on wrong side of clamp bolt. If you clamp the cable on the wrong side the lever arm is changed by more than 50% the result is that you need an excessive amount of force (tension) to shift from small chainring to large furthermore upon downshifting the derailleur spring has a huge lever arm causing a rapid movement with the derailleur crashing into the lower limit with a loud thwack. Easy mistake to make and easy to fix. There should be a visible groove to show you which side is correct but you can also figure it out by looking at the hinging of the derailleur to make sure that you are on the side of the bolt to give the longer lever arm for the tension from the cable and hence the smaller amount of force from your shifter