Small Engines (Lawn Mowers, etc.): my mower keeps surging, revs B7S Briggs & Stratton engine stops lawn mower parts discountonlineparts small engines

Question
Dear Jon

  Hi I have a 3.5 hp B&S and when I start it revs up to full throttle then cuts out, then catches again and revs up burning black then stops burning black then cuts out again. The engine has good spark, good compression (112 P.S.I)
The engine is a 4.5 hp B&S
Model# 10G 902
Code# 03022855
Type# 0189 B1

Mower
Model# 204210X31A
SKU#101-763
Serial# 7515 306432F323
has good spark, good compression (112 P.S.I)

Any suggestions appreciated.
Thanks  Derek  

Answer
Hi Derek, it is normal for the newer engines to rev like that on startup. However, the black smoke signifies over choking. I would suggest replacing the diaphragm below the carburetor. That should fix the problem.  You can find all of the parts that you need on our website http://www.discountonlineparts.com/

Jon
http://www.discountonlineparts.com/