do they feel hard? like the last ones? They should prime as soon as oil starts flowing thru the engine. So they should already be primed if you have started it.
Sounds like from the backfire, it could be misfiring. You could try and run some premium fuel thru it, to see if the noise is reduced or gone. Make sure the plugs are the right ones and still look good. The key here is to continue to narrow the problem down.
Last edited by wiredFocus; 06-14-2012 at 01:43 PM.
Reason: new question