Answer
Aug 12, 2025 - 04:47 PM
If fuel is pushing back out of the primer bulb while the engine’s running, it usually means something inside the carb is letting combustion pulses or excess fuel pressure back into the primer circuit. On a Briggs & Stratton 500E, a few common causes are:
- Leaking or stuck inlet needle/seat – If the float needle isn’t sealing properly, the bowl overfills and fuel is forced back into the primer passage.
- Blocked or damaged primer check valve – The primer circuit has a tiny one-way valve; if it’s dirty, cracked, or missing, fuel can blow back into the bulb.
- Blown carb-to-block gasket – If the intake gasket is damaged, crankcase pulses can push fuel/air into the primer line while running.
- Float height wrong or float damaged – If the float’s fuel-logged or misadjusted, it can’t regulate the fuel level properly.
Best fix is to pull the carb, clean it thoroughly, inspect/replace the inlet needle and seat, and replace any suspect gaskets (especially between carb and engine). New primer bulbs and check valves are cheap and worth replacing while you’re in there.
And yeah — whichever the cause, the manual should get you covered on the repair procedure, including step-by-step instructions, clear images, and exploded-view illustrations.
Good luck!
