Purchased a used Murray select 30577x8A and I've replaced the blade, 4 tires and muffler. It always starts moving with a sudden jerk no matter what gear I'm in. I've tried adjusting the clutch from too loose to too tight, adjusting did not help. I'm wondering if the drive belt is stretched and will only engage suddenly. Any other ideas?

Hi,
Your machine was made for three years for Home Depot, 1998 - 2000 and the breakdown can be found at:
Murray Parts Lists Murray Lawn Mower Parts lists
The first digit of the Date Code on the tag under the seat with the model number is the last digit of the year.
To answer, engagement on rear engine riders is usually fairly sharp. Murrays were made to have the engine sheave (pulley) grip the slanted sides of the belt and often the transmission sheave would grip the inside surface of the belt. Not always on rear engine riders; there would be a broad flat surface on the trans sheave if that were so. You can always start at reduced throttle before releasing the clutch in lowest gear and throttle to full after that and it will shift without the clutch on flat ground. Do have it throttled up with the blade turning since that directly translates into blade tip speed which also determines cut quality.
Peace,
Clarke