Re: head gasket or motor
As suggested, I would try to decarb your motor. Do this, go buy some seafoam, get the stuff that is pressured in the can and the stuff that is not pressured in the can. Pull your plugs and spray some down each cylinder and put the plugs back in and let it sit for a couple of hours. With a fresh tank of gas, pour some seafoam into your tank of gas. Start the motor and let it warm, once warm and with a fast idle "might be more in your case" start spraying sea foam through the throat of each carb while keeping the rev's high enough so it does not stall out. It would probably be easier if you had another person to help in your case to work the throttle. If you can, spray the seafoam into the carbs and kill out the motor and let it sit for a couple more hours. Pull your plugs and clean them after the motor is off and cooled, replace plugs and fire it up "it will smoke like hell, this is the carbon being burnt out" let the motor run and burn it all out, repeat if needed and replace plugs with new plugs once the process is done.
Check the torq on your head bolts as well.
Good luck!
PS having seafoam in your gas will make your exhaust a little more smokey, this is normal and it will also protect your gas as well as keep your motor clean inside!
