PAL Megadrive 1 60hz mod runs slower than 50hz with rbg cable

As the title says, I modded a Megadrive 1 to use a single switch to switch between the 3 settings. with an rf cable 50hz runs fine, the 2 60hz settings run faster music and gameplay but in black and white.
I bought an rgb scart cable to fix the black and white issue and now have colour and faster music, but the gameplay has slowed right down to about the speed it was on 50hz, maybe a little slower. 50hz still runs as it should.
Anyone came across this problem before and have possible solutions? Thanks

 

Which game ? And did you switch without poweroff ?

 

Like Blaasvis said, what game did you use and did you flip the switch while powered on? I think I came across this once when flipping the switch while my Genesis Model 1 was turned on. I was using Sonic 1. I guess it's safe to say never flip the switch while the system is on. It can cause issues with the games and even crashes.

The color issue is because your system is designed to run with the PAL color format over non-RGB connections (Composite Video, RF, and S-Video (requires mod)). RGBS is neither NTSC nor PAL so it doesn't have this issue. There is a mod to fix it but you don't need it since you are using RGBS. If your cable is wired for sync on composite video, try one with boosted C-Sync.

What 3 settings are you using? 50/60Hz are the only two video settings and just need a SPDT On/On switch. If you mean regions, there are actually 4: JP/60Hz (Japan), En/60Hz (North America), JP/50Hz (PAL Asia), and En/50Hz (Europe). Two SPDT On/On switches would be better unless you use a 4P4T (4 pole, 4 throw) On/On/On/On switch or a switchless mod that uses the reset button.