sansoneservices
Well Known Member
For those who forgot what a sniffle valve is, on the bottom of horizontal induction engines it allows pooled fuel, oil, water to drain. Upon startup the check valve closes due to induction vacuum. Mine gave me a fit months ago because in flight with the throttle 75% or more the engine ran great but upon throttling back it ran very rough. Full rich helped some but clearly something was wrong. Going through our normal trouble shooting procedure nothing was obvious.. The sniffle valve open or closed has little effect with throttle open due to induction vacuum and atmospheric being relatively close. As soon as you reduce throttle the open (defective) sniffle valve allows large amounts of unmetered air to be sucked into the induction due to the increase in vacuum. It's easy to overlook the sniffle valve when troubleshooting because it's a simple check valve, normally trouble free.
