Model number R484TR or 31033, it does not have a throttle. I have changed the spark plug. The motor speed is governed by a cam attached to plastic lever via a couple of springs. I will check the fuel filter on carburetor. It does not have a choke but a button which you press three times. I hope this helps, regards Mick.
Need the actual engine model. example(NNN) NNN-NNNNB1. It has one. So you have a primer unit, is primer pushing gas when you pump it? That would cause hard starting. To get it to run faster rpm, the spring tension has to be increased, or the bracket for spring has to be bent. Here is a Briggs pulse/prime carburetor site. Look at the first two shown.http://outdoorpowerinfo.com/repairs/briggs_stratton_carburetor_cleaning_repair.asp