Does it have the stock (Heavy) flywheel on it? It would be difficult to
detonate the engine without a load and at least partial throttle. More
typically it takes wide open throttle to do it. But low RPM is not
protection against it. My driver has done it right off idle. With just a
flex plate the engine can shake the transmission in acceleration and
deceleration hard enough to sound like it has rocks inside it. With the stock
flywheel this is not possible. Typical race car idle is at 2,000 to 2,200 RPM
with no flywheel mass to avoid trans damage.
That timing is fine. anywhere between 20 and 27 degrees is fine. It can be
fixed at those numbers and still start and run just fine. The lowest octane fuel
is fine.
Check the timing on the trailing (upper most) plugs to be sure that they do
not fire ahead of the leading (lower) plugs. If there is a timing split at all
the trailing must be behind the leading. For your operation the stock
plugs are a very cold heat range and with no load to heat the plugs, fouling
will be a problem.
You can run a conventional looking street plug medium or retracted tip with
no problems at all. For a high load like a prop, then you need to go back
the Mazda plugs.
The sound you describe sounds like a cross fire or a light detonation. So
put a timing light on all 4 wires and see if the sound is coincidental with one
of them firing. The split timing helps torque just a bit down low. With the RPM
that will be used in aircraft leading and trailing at the same time is simple
and effective.
Dress the wires well away from each other. Is it a direct fire
ignition?
Lynn E. Hanover
In a message dated 3/10/2008 3:17:31 A.M. Eastern Daylight Time,
tomk@telus.net writes:
My question is
regarding the noise that I hear. Has anyone experienced such a
noise? I have noticed the engine missing sporadically at low
RPM's with a load on it, and the fuel/air mixture gauge showing five to
six LEDS. Can a miss, detonation, bad timing, fouled plug(s)
etc cause such a noise? My timing is very close to 23 degrees
BTDC. When I turn the engine over manually (i.e.,
with socket and ratchet) the engine feels like it has good compression, and
doesn't make any strange noises, such as, anything broken or loose
inside. I may tear the engine apart to inspect the
inside, later this year.
Thanks,
Tom