Clams Canino wrote:
wrote in message


Anybody know the point of intentionally running on only two out of
four cylinders?
Related question, how do the non-firing cylinders receive lubrication
without pumping raw fuel/oil out the exhaust at low rpms?


They are firing, and getting a fuel/oil mix. They are just not getting a
sufficiant amount of said mix to actually *combust*, so they remain
"passive" until the revs come up and they start sucking from the main jets.

Why? I've never gotten a totally straight answer. I know that unlike all
the 4 cylinder cross-flows Mercury did, this looper will *not* run correctly
at low RPM on all four. I gather it suffers from harmonics and bad
vibration. And from everything I've read, it's an inherant problem with no
work-around. I don't know what kind of spin Mercury Marketing puts on the
2+2 angle, but the fact is, it was the only way they could make it run right
at all.

Conversely, thier three cylinder 90 (same motor just a three) runs fine at
idle on all three. I think that much like the 90 is kind of 1/2 of the V-6,
that Merc should make the mid-hp motors (100-125) half of the larger V-6's
and scrap that 4. I'll not forget to mention that they had a perfected
100-140hp powerhead untill 1989 when the 2+2 emerged.

-W



The story I heard was it had to do with the port timing and the exhaust
configuration. If both of a pair were running at low speed the exhaust
blew back. 180 crank. one fires with other at bdc. Maybe even spits
back out the carb.

I have one of the 115. Been ok.