RE: Welcome to Club SAITO !
CU:
If you measure the outside diameter of the intake pipes, I think youl'll find the older one is larger. Saito decreased the size to keep the air flow higher, giving more consistent running. They did not alter the cylinder to match the smaller size, that's where our current vibration and intake leaks have come from. At least that's my opinion.
First ran into this with an FA-80. Had a dent in the intake pipe, ordered a new one. When it got here it rattled around loosely in the head. I reused the old one, the new one is in my parts bin.
If you do find your pipes are different, you can order the later replaement.
While the difference in the muffler is there, I don't think it will make any real difference.
Bill.