Did I screw up my crank?

I wonder if I filled in those holes if it'd run fine again, being that I've lowered the vacuum difference the transfers dont fire into the cylinder as quickly and significant amounts of exhaust gases make their way back into the cylinder at low RPM's, causing the poof and firing issues. Only two ways to find out: fill in the holes, or get an expansion chamber. apparently 1.5:1 case to cylinder volumes is ideal, "stuffing the crank" causes transfer pressures to be increased and fire fresh mix through the cylinder and straight into the exhaust at low RPMs, wasting fuel and ruining scavenging, causing a narrow power band. Because of my increased compression head and lowered compression crankcase, I've ruined that ratio, likely by alot, probably around 2:1 now, pushing the powerband so narrow and high the motor cant get past the low RPM vibrations of the drilled crank.

I'm reading through Gordon Jenning's 2-stroke tuner handbook. It's quite interesting. It states the bigger the exhaust port is, the more power you will make, no exceptions. The issue is with a bigger port you run greater risk of catching the piston rings and destroying them, you could put a vertical bridge in the middle of the exhaust port but because there's less material it'll expand disproportionately and potentially put pressure on the piston, as well as less contact with the [relatively] 'cool' cylinder wall thanks to a bigger exhaust port will cause the piston to endure more heat. However 62% of cylinder bore is a good safe zone, some high performance motors go up to 70% and some bridged ones even overhang the transfers (maybe 80% bore width to make immense power, but because of heat, sacrificing RPM. To put it simply, our motors have a 47mm bore and run a 24mm exhaust port, or 51%. According to Jenning's studies, we can safely widen the exhaust port to a whopping 29.14mm wide (internally). If you choose to do this, curve AND bevel the top and bottom of the port to push the piston rings back in place as it goes by. Before such an endeavor, port match your intake to 24mm (if you're running a Super rat or GT5-a, then you dont need to, it's already done). As for crank pressures, the optimal ratio between the cylinder and case crank pressures is around 1.5:1 cylinder to case. More or less you're simply losing power, so stuffing will only help if you've raised your cylinder compression (shaved head or aftermarket head) or if the ratio was off to begin with. This came about because of an old moped that had a ratio that was way off (about 1.2:1), and people discovered stuffing the case caused increases in power, this carried on through today as people assumed it worked for every motor. Modern motors are already affixed to this ratio, whether or not the HT's are, is another story. The last thing you can do to these motors without having to buy aftermarket parts is correct the transfer port shapes. A sharp angle transfer port "roof" increases high end power (our HT's appear to use almost an 80 degree roof). Shallowing it out to say 60-75 degrees will lower the power band. Also aiming the transfer ports toward the intake will help the "loop scavenge" design, pushing the exhaust gases out more efficiently. You'll notice only one half of each transfer is actually aiming toward the intake port, the other half is nearly aiming directly at the opposite transfer port (it's actually a few degrees toward the exhaust port). You dont need much, but JB weld in the top of the transfers to aim it toward the intake side will help make scavenging more efficient. That said, I DO plan on creating a steel insert (or perhaps a base gasket with the inserts on it) to correct the transfers for those who are less dextrous or more feeble about modding their motors.

the inside of the cylinder? it's not brittle at all, its actually quite soft, takes easily to gouges if your hand slips while grinding away at it. It's easier to get through the cylinder than the piston.