Topic: The highs and lows of old bikes

[seanbarney41]

I just went for a blast on this...too damn loud and that yoshimura pipe has always made an untuneable (by me anyway) flat spot...but I love it.  I will never sell it.  It will be the last bike I own.  Whether I can ride it or not.

Tough looking bike! The color match the black very well.
Yamiya sell diffuser that might fit the 4-1
https://www.yamiya750.com/index.php?main_page=product_info&cPath=142_88&products_id=833&language=en

thanks PeWe...I am quite sure that diffuser is just what I need.  I took that bike to view an AHRMA race once and got to talking about it with an old racer who claimed to have met Pops Yoshimura back in the day.  He scoffed at all the reproductions available with baffles claiming that Pops had never intended this pipe to have a baffle.  I don't know who the racer was that I met or if he was telling tall tales.  I generally listen with interest to my elders whether they are exaggerating or not and try to find the useful information in their stories.  So, I leave the pipe uncorked as a tribute to the guy who may have originally built it.

That right there...has got to be one of the main highs about old bikes, the stories and wisdom of old guys that mastered concepts years ago, concepts that we are still struggling with today.  A brand new gsxr1000 is not as likely to encourage such conversations.

[PeWe]

I think the street versions had diffuser in early 80's. I read a test in a Bike magazine then. I had thoughts to buy it. I bought an RC 4-1.
 Completely open, no candidate for that test.
Different with race 4-1.

CB750 sounds very nice with 4-1, but very irritating in the long run when too loud.

I think that type of diffuser without the wool would sound nice. Not too muffled.

But, there is a hole in your pipe for diffuser screw?

[seanbarney41]

Yea, there is a lot of debate whether these very early yosh pipes even came with that straight end section originally.  I am of the belief that it was left off, or very short so that the owner could tune the overall length to the rpm range that best suited their engine, gearing used, etc.  But none of this is suggested in old catalogs.  Maybe pops included instructions when new?  I doubt it.  I think pops was far enough ahead that he just figured, "if you don't know already, nothing I do is gonna help"  ha ha