Hi everyone,
so at the last race of the season the engine "cooked" the JE pistons I was using (DP62/r) and now I have to change them. The engine is running quite hot (the upper part of the conrods was purple, and the piston pins has typical overheating purple circles), I guess because of a quite high compression ratio (12,5:1).
While brainstorming with Yossef, it has also due to the fact that my current configuration has little or zero squish, so it requires a quite high spark advance (40°).
I'm looking to install Kawasaki KZ650 pistons, which are almost a perfect fit for the CB750 (apart some valve groove work to do). I've also bought a set of Yamaha XJ650 pistons, that are 63mm in diameter with a nice dome. The only main problem is that they use a 16mm pin :-(
Does anyone here have bored out the conrods to fit 16mm pins? Seem pretty feasible to me... especially since the kawasaki kz650 pistons, the yamaha xj650 pistons and the JE pistons I was using have the same weight.
Also, how much squish are you guys using and how have you achieved it? Looking at the piston and head configuration there's very limited squish to achieve within the 750cc displacement...
Ciao!
Riccardo