Hello
POI and
NormThis has been asked before.
The Imperial had a spacer between the cylinder and cylinder head.
This reduced compression and made for a cooler-running engine.
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=62325Victa Zoom Outboard was 50:1 and I believe that ratio to be the best
for imperials.
But I do note that Victa did say the machine would run on 80:1.
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Jack