Hi to all, can anyone advise me of the correct spark plug for a standard 1989 1200 sporty. I have had plugs replacedwith NGK DCPR7E plugs a short time ago. I have new leads fitted at same time. Bike back fires when running through exaust? I am happy to have other brand plugs but think I hay have the wrong plug at this time. Any suggestions appreciated. Thanks Roy (From down under)