question

I am rebuilding the top end on my new to me 1975CB750. The exhaust collar on cylinder 4 has some sort of hard rubber on the inside of it. Its just over 1/4” thick and runs through the entire collar/flange. There is no other visable differences in the valves or cylinder head. My question is...

Hey all, I'm going to look at a 1979 CB750 10th Anniversary edition later today with the intent of buying it. I just wanted to reach out to the community and see if there are any things in particular I should look out for. It has 6,400 miles, the seller has owned it for 17 years and has put...