My take on it is that there is still combustion occurring on the intake =
stroke=20

The incoming fuel ignites while the intake port is open (and the exhaust =
is closed)
- therefore the gas exits via the intake.

Taking the timing towards TDC will give a greater burn-time and avoid the =
scenario hopefully.

Eoin

>>> alan@MICROTIMA.CO.UK 05/20/02 10:50AM >>>
>> How does this explain the 'backfiring' behaviour I observed at the
>> retarded
>> ignition point
>> and how will advancing the ignition slightly cure this?
>>
>I suspect you were slowly filling the exhaust with fuel during your =
attempts
>to start it.  With very retarded ignition, the mixture is still burning =
when
>it exits the exhaust port, which ignites the fuel stored within.  The =
result
>is a backfire, quite an impressive one on a full size engine :o)


Well, I doubt it!    ;-)
I've been running the engine with an open exhaust port so there has been =
no
place for a liquid fuel charge to collect.
I mentioned earlier that at the retarded ignition point the engine was =
firing=20
every flick of the prop, so it must have been partially burning the fuel =
in the=20
combustion chamber?
Thanks
Alan

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