1980 CB750F Cafe Racer

[Zulu- Boy]

Hi all!
This is my first post here, and seems like a awesome forum. Just the kind of one I've been looking for.
Here's the thing, I've a acquired my CB in December, and I'm not going to lie, there's a lot of work that needs to be done to it, from the electrical, to carbs, to dash/controls but that's why I've chosen this project. I've done a lot of research and I've decided to do a cafe racer conversion. The thing is I just want to know for know, is what the bes exhaust system that will maximise my power output and make the most amount of noise, without losing precious power. I was thinking a 4 in 2 exhaust system with 30mm manifolds, to a something like a 55mm branch to a 63mm tailpiece. I would greatly appreciate your criticism.                                                                                                      Regards.                                                                                                                                 Zulu- Boy

[seestheday]

Welcome to the forum

Unless you have a lot of experience working on bikes.  I'd get the bike running reasonably well before doing the cafe conversion.  Just saying...

Not sure on the exhaust, sorry.

[shinyribs]

Welcome zulu

I agree with Sees'. Getting it running and sorted out before you start modifying. It really does make life easier and will probably save you alot of time and money in the long run. BTW, what year bike do you have?

As far as exhaust I'm not sure what will make the most power either. The general consensus is a 4-1 makes the most peak HP. 4-2 is good for low-mid and 4-4 is a good all around balance. I had one bike that had a 4-2 on it that i removed for drag pipes. The drag pipes ran better at every rpm compared to the 4-2. But,the 4-2 was baffled and the drag pipes..well,they weren't

4-2 have a little bit of a deeper tone to them whereas a 4-1 gives it a more sporty sound. Very much like the modern inline fours. That's all I know from personal experience. Never had a 4-4 setup.

Again,welcome to the forum and start a build thread when you get around to it See ya around....

[Zulu- Boy]

Hi. Thanks for the input. Its a 1980 model, with the DOHC. I do know enough to refurbish the bike. And I have a lot of helpful contacts. On the matter of getting the basics done before I start modifying it, I need a new exhaust system, so might just well get the exhaust I'm going to end up having a little ways down the road. But al is appreciated.
 

[seestheday]

Cool.  We've just seen too many people start a job and not finish it to not warn people .

Where is your build thread?

[Zulu- Boy]

Thanks for the advice, I'll do it... Wait, how exactly do you do it?

[seestheday]

This can be your build thread.  Just start uploading pics and detailing your progress

[Half-Caf]

I second the need for pics! And welcome to the forum
I'm not on here a whole lot anymore, but if there's anything I can help out with I would be glad to do so -we've got a good bunch of guys here, too.

[Hoosier Daddy]

Welcome Zulu_boy!

 I just gotta chime in on this one but you might find better advise from someone else. . I will start out by saying factory carbs on our DOHC's are going to be your limiting factor. Stick with the OEM airbox because of the way the vacuum manages the pistons height againdst the spring pressure in the top of the carb, that is what controls the needle in the main jet at various throttle positions.
 If I had my choice I'd be looking for a vintage Kerker system and here's why... Kerker got hooked up with Supertrapp in the late '70s / early '80s and if you are a gear head of any type, you've heard of both. Supetrapp mufflers (silencers) are TUNABLE.  You can easily change the amount of back pressure by adding or removing the discs that bolt to the outlet (no baffles or packing). The more discs you put in, the more openings there are for exhaust gasses to pass through and therefore louder sound.
 Less discs (5-6) give you more torque / better midrange, while more discs give you more top end Horsepower but tends to get too peaky at the extreme (9 or more). You can play with it to get the best seat of the pants feel and plug chops to see if your close on the jetting because you can run her too lean (BAD).



  I got 8 in my '80 Zook GS750, but it's got Mikuni's rejetted a couple sizes up and a free flowing Uni air filter attached to the factory airbox. Nice usable power at the midrange for around town with a mild "growl"... but when you grab a handful of throttle... DAMN!
 You might also try keeping your eyes open for a genuine Yoshimura system, not Carpy's "yoshimura style".  Authentic Pops Yoshimura exhausts are what the Japanese Factory Race teams used back in the day... Started with Kawasaki, then Suzuki, but also made them for our DOHC Honda's...but you might not want to take on a second mortage IF you find one....pretty scarce and desireable, but they ARE out there.

 

[Zulu- Boy]

Tanks for the advice, this is now officially my build thread. On regards to hoosier, I'll do some research on what you said,