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Fairbanks-Morse Z


I have a Fairbanks-Morse z 2hp spark plug model with a rotary magneto . My question is I got it running but it spits gas out of the flutter valve while it’s running ! What is causing this ?


One Millionth Post
Last Subscription Date
Intake valve not seating? Weak valve spring or stem gummed up resulting in slow valve seating?

Kirk Taylor

And that would cause it to spit out of the carb ?
Spitting out of the mixer indicates that pressure is coming from the cylinder. The most likely path for that is past the intake valve. If the intake valve isn't seating properly, it will leak compression and combustion gases into the mixer. If the intake valve is sluggish in closing due to either a weak spring or a gummy stem, the valve will still be partially open when the piston begins the compression stroke forcing air back past the valve and out the mixer. If the valve is leaking (as opposed to sticking open), it can usually be heard as a slight wheeze or hiss coming from the mixer when the engine is rolled up against compression.
Oil the valve stem and pull out lightly in the spring to put a little more tension on the valve while the engine is running. If the spitting stops, order a new valve spring.

Andrew Mackey

Last Subscription Date
A worn intake valve guide will do the same thing - the valve will not seat properly all the time. grsp the valve stem and see if there is excessive play - it should not wander in the bore. Excess play will mean replacing/boring and installing a new guide.


I slapped the valve and installed a new spring and it runs like a champ now ! Thank you everyone

---------- Post added at 05:26:43 PM ---------- Previous post was at 05:25:31 PM ----------

Sorry I “lapped “ the valve !