Kevin,
I’m sure you are aware that many carbureted
intake systems can have a strong “stand off” wave that keeps a “mist/cloud”
of fuel particles riding a standing wave in front of the carburetor intake.
This may only occur at certain rpm – but is almost certain to happen at
some (several?) RPM values. When you capture/confine that mist of fuel in
a plenum/cleaner box – it can provide a ready source for Ka-Pow –
only looking for an ignition source. Frequently if you take off the plenum
box you can actually see the mist of fuel dancing in front of the intake.
The source of ignition can be several –
improper ignition timing is one, on the older 13Bs with the overlap between
exhaust and intake parts of the combustion chamber, it was not unknown for a
glowing carbon particle to touch off the intake mixture prematurely.
Keep the fire extinguisher handy
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of kevin lane
Sent: Sunday, May 02, 2010 11:50
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] ka-pow
my new engine has been hard to
start. the other weekend I experienced a big bang [backfire I
guessed]. today I noticed my intake manifold has a bit of a leak!
my design assumption that it would always be in a slight vacuum state was
obviously wrong. need to check the carb I guess to see if anything
happened to it.