I work on lift trucks 40 years the electric primer button is there if you need to prime it for a blast of propane but if the machine is running good it will most likely start most people installed a button on the dash if they needed to prime it for hard start in the morning. You could use the start circuit on the starter as it cranks it would prime the carb and when it starts the start circuit is off wire a relay if it does not have a R post on the starter. Good luck.