Hi Finn,

What sort of coils are you using.  Are they factory Mazda rotary coils?
What sort of triggering mechanism/ignition modules/drivers are you using?
 Are you using a distributor or a crank angle sensor?  I have no idea what
you are using so I have to ask the questions.  If the coils ARE getting
hot,  put them in the breeze!

You are spot on that an intermittent ignition will blow a muffler to
pieces.  Many years ago,  one of the local peanut brigade (he used to work
for my opposition) used to have great fun coming down the hill outside my
old shop,  momentarily switching off the ignition,  pumping the accelerator
like crazy,  and then switch the ignition back on.  Really impressive at
night!  There would be a spectacular blue/yellow flame several feet long
out the back. It would light up the whole street!  The third night he did
it,  it not only took off the muffler and the rest of the exhaust,  but got
him booked by the local constabulary.  A cop just happened to be going the
other way!  Anyway,  I digress ...

But yes,  to answer your question,  two or three decent momentary ignition
on/off incidents are guaranteed to remove any muffler!

Leon

Bill Freeman wrote:

  Finn,

  An old trick to make a lot of noise (and probably blow up the muffler) was to
swithch off the ignition while the engine is being driven by the wheels (pumping
fuel/air thru it but not igniting it) and then you would get a nice BANG
when the
ignition was switched back on.  Perhaps you are right and your ignition somehow
cut off momentarily, filling the exhaust system with fuel/air mix and then
the ign
came back on and ignited it, blowing it off of the plane.

Just a theory, see how it fits with your extra facts that I don't have.
Good luck.

Bill

Finn Lassen wrote:

Thanks Leon and Bill.

I guess now that I only have a 2" unmuffled (SS flex) pipe I won't have that problem,
just more noise :)

Today I checked spark plus and harness. BTW, how thin do you let the center electrodes
become before replacing the spark plugs?

I use the stock Mazda coils controlled by Tracy Crook's ignition controller.

My drive belts were loose to the point where I could hold the water pump pulley with
one hand and turn the prop with the other and belts slipping. I tightened them a bit.

Didn't have space enough between firewall and e-shaft pulleys to measure end play.

Couldn't measure compression - my tester is leaking.

Looks like part of the dacron had been sucked in through the carb. Need to device some
other way to even out the airflow to the carbs.

After running the engine at 4400 RPM for a minute or two with the plane tied down and
everything looking normal (that thing is NOISY without headsets!) I decided to do a
little test flight. I stayed close to the airport and didn't open up to more than
about 5200 RPM. No abnormalities, except the (usual) 80 - 90F EGT difference when
opening up the throttles.

I still have that annoying (minor) oil leak between oil filter pad and homemade cap in
spite of replacing o-rings. I guess I need to get it properly machined - I cut the
counter bores for the o-rings with a 3/4" foster (wood) bit.

Finn

Look carefully for cracks in the end housing in that area of the leak Finn.

Speaking of two inch down pipes after the collector, engineer Ron at Star Mazada 
said anything less than three inches and you are losing power. They should know
they build 40 race cars a year and have a chassis dyno.

I stopped in there again today to show them the teflon encapsulated silicone O-rings.
They are real excited about these O-rings. They have a bit of trouble with the stock
O-rings.

BTW they have some parts that they will sell us such as aluminum dual belt
e-shaft and alternator pulleys. 
More on this next week with pictures as they 
are off to Phoenix for the races on Sunday and Monday. See them on the Speed Vision
cable channel.


Paul Lamar
 
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