I like the gusset work on your frame. Was it converted over to the 88-90 A-arms?
Back to your question, you might want to try a bigger rear sprocket like a 40 or 42 then try the race again. The FMF is not a drag race pipe but is not POS either. Just make sure you are running race fuel & that your carb is jetted accordingly. You didn't mention whether or not you was running an air box & lid or not. This makes a difference in output. Also, those dumbo ear front fenders probably slow you down quite a bit.