Something the Team has seen on all the China Bikes they have worked on is the restriction of the bubble weld in the Exhaust Header Pipe and therefore we could not rest the tear down until we investigated that issue and sure enough it does have a bubble weld in the header pipe that is slightly restrictive. The opening at the bubble weld measures 24.47 mm roughly across. The Head port exit diameter is 26.73 mm so roughly 2 mm restriction. I used a Dremel tool with a carbide cutter to cut the bubble weld back to pipe diameter with a slant toward the head exit opening with a final I.D of 27.7mm.
SAFETY: If you choose to do something like this be very careful and use protective eye and mouth protection. You can see those small sharp shards, very small, that will stick to fingers etc and you would not want to breath them in or get them in your eyes. I usually get one or two in my fingers and have to use a tweezer.
The header pipe O.D. at the head is 39.47 mm and the tail section where it enters the muffler joint is O.D. 31.9mm and I.D. 29.63. The Muffler joint is I.D. 37.38mm and there is a graphite gasket.
The muffler exit I.D. is 19.32mm so maybe this exercise has no final end improvement? But the team is of the mind to increase efficiency at every opportunity.
Exhaust header gasket was constructed of rolled metal with graphite coating shown in comparison to new header gasket which measures 39.97mm and is a spare gasket I had for the HAWK. The X Pect header pipe to muffler is a couple of mm smaller than the 230cc CG motor in O.D. and I.D. but the Header pipe is thicker where it joins the head to make up for that and it therefore fits the same gasket as the 230cc CG motor.
A picture of the exhaust port. Looks like there is some airflow to be gained there with some Head porting.
