KE51, I get 7,900rpm using a Topflight 9 x 4 and 6,500rpm using a Topflight 10 x 4, fuel is Modeltechnics D1000
http://www.modeltechnics.com/diesel.htm Didn't notice excessive vibs on my 'curry' Mills 1.3. It neede some attention when I got it from the 'bay as BNIB. It had a pourous crankcase casting that was fixed by the application of metal filled epoxy. You could try the old trick of moving your prop 180deg. Assuming your prop is in line with the piston /conrod/bigend bearing at TDC, loosen prop and rotate 180 whilst maintaining position of engine components. One way any prop out of balance may be adding to the reciprecating out of balance, the othe way it will help to balance the reciprecating out of balance. In the past some would use a deliberatly out of balance prop and position it to get the least vibs. As to Indian Mills conrods, I believe they are made out of dried chewing gum and rice!