Soooo... just rebuilt the engine, new seals new gaskets, new everything. I have a ported set up with a 15.15 sha and a shorty intake to match. Before i was having issues and decided to rebuild the engine i was hitting speeds of about 35-37 mph... now I hit about 30 and it back fires like a bitch... Tried running with and without an air filter.. should i downjet or what do you think it is?