While the weight of the rod increases slightly as well as the total reciprocating weight, there is a significant decrease in the forces acting on the crankshaft. This is due to the reduced angularity of the rod at the 90 & 180 deg points.
Jim , while there may be a decrease in forces acting on the crankshaft I would consider the increase in recipricating mass as a definite disadvantage in our small engines. Any increase in reciprocating mass is going to reduce available operating rpm and add more stress to the crankshaft, bearings etc. A lower reciprocating mass is all gain no pain.
Emissions From Two Stroke Engines by Marco Nuti, pages 146 to 149 explains in detail the effects that BORE DIAMETER/STROKE ratio have on scavenging & trapping efficiency in loop scavenged engines. There is also information in the Blair & Bossaglia books. Typical numbers range from .8 to 1.4, with a slight improvement with lower numbers. In my engines with bore of 1.125 & a .902 stroke, the ratio is 1.247.
Jim
Jim, You seem to be running a very oversquare engine which goes against the practice of most GP two strokes and high performance kart engines which use bore/stroke ratios of very close to 1:1. The port area available in a two stroke engine is proportional to the the cylinder wall area not the head area. In a two stroke this favours long stroke/small bore up to a point.
Dave