I've been riding this grande for about 3 days, ran/started great until after work tonight. I made sure to measure out the oil 50:1, and again ran great prior. It is really hard to pedal and makes no spudering sound like its trying to turn over. could it be bad spark plug? would that explain why its hard to pedal? or....is it seized up....? it has the "25" sticker on the sub-frame, ran that mph, and had the correct oil mixture so i don't know how it would seize. Help please!!!