3 Holer 2 Carb Merc or Mariner have the same repute as the Firenza was to cars! Junk
I went through screwing with half a dozen of those 3 cylinder 2 carb blocks and 4 of them did that to the top cylinder destroying the piston and the head every time no matter how much extra cooling we fed in at different points or took out of others spots knowing it had that problem. The last two complete blocks (no carbs or ignitions) and all their spare long block parts (no carbs or ignitions either, they are worth something) from the other 4 went into metal recycling (my neighbors took them in and bought beer with the proceeds) this last spring as even the dealers didn't want them back even though they were overhauled and fresh!
To begin with when I asked my marine dealer friends for these engines to test for FE, they thought I was nutz immediately. They told me I was wasting my time from square one. They gave me complete powerheads for free, take all I wanted!! They told me if a person wanted to loose customers you sold them a Merc or Mariner 65 3 Holer 2 Carb and they the customer would be back for warantee until it ran out which made them madder still and then you lost them as a customer permanently. They were that bad a motor! A very ill concieved deflector using dated technology well past its design use.
One dealer had a complete Merc 3 holer with a for free sign laying by his inlet road for 3 years and no one took it! Finally a grader wrecked it when it tried to make it part of a snow bank clearing the road in winter!
Enough said. :mad:
"Blow Through .......it blows".
That method works, but it does NOTHING for fuel EFFICIENCY . The carb or injector feeding INTO the intake of the Supercharger can actually increase fuel efficiency , as well as make a big boost in power . I always liked the idea of a centrifugal supercharger or turbocharger which had an aircraft carburetor (adjustable fuel mixture ) mounted to the intake side of the charger, naturally having a pyrometer in the the exhaust to read the exhaust gas temp. And before someone complains that it's too complicated, NOTHING worthwhile is easy !