MicroSquirt.com read only forum (Jan.15,2018)

I'm having an issue with my MicroSquirt on an aircooled 2.1l engine. It runs great above 2000rpm, but if I let the RPM drop to around 1500-1700 rpm I get a pretty severe bucking which tosses you in your seat. I'm not sure about the configuration of the engine, but I do know it's been rebuilt to non-stock specs. The MicroSquirt is running the latest firmware, uses a VR sensor, and has LS2 COP ignition. Oh, and I don't recall 100%, but I don't think the engine did this with the dual carbs.

Thanks for any tips or ideas...