i just bought an 89 prelude si for winter, cars in great shape but it seems like the previous owner kept fouling out the plugs. i just replaced them with some NGKs. i just wanted to know what would cause it so i can prevent it in the future to make sure it doesnt happen to me. thanks for the help.

 

If you have the Chilton's repair manual the whole back cover shows what problems can arise from the plugs, match up the old plugs with the pictures and the back and that will tell you

 

Make sure you are using the correct plugs. If you use colder plugs, they will foul out.