Robar: Slow down a little , yes you know the plug size NOW along with the correct Gap , since Tom was nice enough to take the time to forward this info to you on a previous post. How about having the grace to go back and Thank Him accordingly on your previous Tuesday Thread . There is proper etiquette on this Forum . The info and advice is free , so is a little atta boy to Senior members Duh !

I believe ALL Lawnboy 2-cycle mowers in the 21" size from the late 1950's to the end of 2-cycle production take the same replacement blade. This may not be true for the more obscure "M" series.

It takes the regular 'Tri-Cut' blade furnished on all late LB 2-cycles - no special 'mulching blade' is recommended - stick with OEM. It should also have a 'mulch fan' mounted under the blade (blade goes on first, then mulch fan). The 'Silver Series' has a steel deck with bagging available by installing a bagging kit which includes the chute that replaces the mulching plate in the top front of the deck. Side discharge is available with a 'blank' plate, and of course the mulching plate blocks the discharge chute. Wash and re-oil the air filter. Use oil at 32:1 (8 oz/2 gal with Lawn-Boy oil, if still available).
Post questions if it doesn't run right - I don't have one anymore but I remember the things to check/adjust. Typically they are set a little lean for EPA concerns, which of course is not good for running or longevity.