Briggs and Stratton 450 series starts but won't run. Why?

Use a business card. That's just about perfect for the gap.

check for the small wire to the carby that makes contact when the throttle is in the stop position is not shorting out

there are holes in it should be three or four. a rubber diaphram is covering it but they are there

Can you get me the lawn boy Model #

to me that sounds like a problem with a bad coil

that engine uses a fin style governor remove the upper cover and see if there is a nest or something holding the fins movement

trry a shot of starting fliud see if it wont start then make sure your getting a spark to

Standard oil for the briggs engine is an SAE30 grade

go to replace pull cord follow instruction

The Briggs and Stratton 450 series is the engine (4.5 Hp). Is there a model number on the mower deck anywhere? I can probably find you a manual but need that model number. Unless you just want an engine manual.
Murray makes a 20 inch MX450 that has the Briggs and Stratton 450 engine on it but there are numerous makes and models (self propelled) that use this engine.

MX450 parts manual is here:
http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=lminvFXBnfBhU7y

If you can come up with a good model number I will search avidly for a manual.

Thanks for choosing FixYa,
Kelly