2000 Powder Special 600 Efi Ignition Questions

i have a 2000 powder special 600 efi that runs great at high rpm say 6000 or more but at low speed or after hard exelleration it tends to bog out some times and you have to feather the throttle to even keep it runing. and it will sometimes backfire, also the plugs are new but i am changing them again to see if it helps. any help would be great. also is there a way to check the ecm for codes other than a computer connection thanks.