I have an older Tru-Test snow thrower with a 3HP Briggs & Stratton motor on it. The only way that I can get the unit to start, everytime is to unscrew the spark plug, pour in a shot of gas, and put the plug back in. It will start everytime this way. It appears that the manual choking system is not working. I am not an expert on Briggs & Stratton equipment and I am not sure where to start investigation.