the 2nd gen im buying has a 2.0SI sticker on the back of it, and the guy said it was a 2.0SI but hes not a prelude fan hes a Jetta guy and his dad bought him the car in December so I doubt he would know the difference. But it has the normal windows, not power windows, and dual carb, which leads me to think its a 1.8 Normal lude.
No such thing as a carburated SI lude. 2nd gen used a fuel infected A20A1 in the Si, 3rd gen used a fuel infected B20A5 in the Si, and carburated B20A3 in the S until 1990 were the Si used either a B20A5 or the B21A1, depending onoption package
Whats probably happened is that previous owner like SI spoiler and nicked one from scrapyard and fitted it to his car. Sold to another owner who new jack all about cars and thats that. Just tell him it's not an SI but a base model Carb 1.8 and knock him down in price if you thinks he's overpriced, if the chassis is good with minimal rust and looks like it's been looked after will still be a good buy more can be done with the carbed model although the SI does look better as it' has more modern looking colour coded bumpers and tail lights.