My 93 750W will only run on prime. The petcock is new and the vacumn line is not clogged. Any ideas?
Put a piece of fuel line on your petcock, disconnect vacuum line and draw a vacuum on the vacuum line with your mouth.
See if it flows in the "ON" position.
If it doesnt, you have a petcock stuck diaphragm issue. If thats the case, you'll have to pull the cover off the back of the petcock and free up the oring on the diaphragm plunger.