I’m looking at an 87 LT 500 that has had a recently blown head gasket that was repaired. The base gasket was not replace. Now there are bubbles coming from inside the radiator when the machine is running. Are the bubbles being formed from a cracked jug, the base gasket, or else where? Keep in mind the quad runs perfect.
Thanks for your thoughts.

 

Bubbles are caused from pressurized air entering the system, cracks in the cylinder would most likely cause coolant weeping/loss rather than bubbles. I suspect that the head gasket is leaking again. The gasket mating surfaces may need decked or lapped to ensure that they are flat. In rare cases I have seen when a cylinder is resleeved that it can leak from between the exh port roove and the coolant passage, but again this usually shows as coolant loss rather than bubbles in the system.

 

The quad probably needs burped. When the guy filled up the radiator, it wasn't clear full. Take the cap off the radiator, top it off, slowly stand the quad up on end, and this should let all the air out of the system, then set it back down, and top it off. This is just a suggestion, hopefully it's just something simple like this.