Two Questions for You; Frame and Carbs.

[MHluv2ride]

My first question is about cutting unnecessary pieces off a bare frame. I am building a cafe racer/ brat (haven't decided what to do with the seat yet) from a stock 1981 cb750k. I currently have the frame stripped and sand blasted to be powder coated, then realized, if I plan on de-cluttering the frame and using a seamless "U" style seat, I ought to do it before finish work, duh. So...since I am brand new to bikes and building my own, I would really appreciate some advise. I've searched this forum for frame cutting and haven't yet come across the type of cutting that I am referring to. Anyone out there know of a diagram that shows what each piece on the frame is for and/or a cutting instruction type diagram.

Question #2 has to do with the carburetors. I have stock Keihin carbs right now that I am completely breaking down and cleaning (learning as I go, thanks to people on this forum) and replacing most gaskets, jets, etc. My question is: Once I am done with the deep clean/ rebuild, and assuming they function correctly, could I sell the 4 carbs and make enough to convert to a Mikuni 2 carb system? Are stock Keihin carbs in demand if they are in excellent condition? The reason I ask, I am interested in running pods and understand the Keihin carbs on the DOHC cb's require a constant vacuum and filter system that the stock airbox can only provide. I'm only interesting in acquiring information right now, for my main goal is to get the bike finished and running for the return of the sun. Gotta love WA!

Thanks for the help!
Mike

[Hoosier Daddy]

The seat hoop is a common cafe' / brat mod. Your best to get one bent up a little long, then decide your cut points on the frame and hoop together, slug it and weld it up if you are capable, have a pro do it if you are in doubt. It also sounds like you are going for an open triangle, If that's the case you won't need the side cover tabs.... and running sans chain gaurd? wont need those tabs on the swingarm then.
 But before you do all that you ought to decide what seat style, bought or home made. If you want a bum-stop cafe style you can relocate the electricals under the hump... but a Brat typically has a flat seat. Much harder to hide the electricals so you may want to keep the side covers.
 Search GSX carb swap on CB750's. The Suzuki 4s used Mikuni's and it is fairly common swap to be able to run pods. Now, nothing will be a bolt-on swap and there will be some fabrication / jetting changes needed.

[MHluv2ride]

Thanks Hoosier Daddy, now I know where to start.

I’m torn between the two seat styles; I really like the silver cb750, seat & tank style you posted as well as the 750 I posted. I've actually been going back and forth in my head, for a month or so, on which I would rather use as a "reference" for my bike. Of course it will be different in certain ways to make it my own, but you know..



As far as welding, I’m learning right now, so I'll probably have a buddy do it this time. Next bike will be all mine! I was thinking, if I decide to go with a seat cowl, I could put the battery underneath and electronics under the tank. I've only read about this set up on other bikes and this is what my girlfriend is working on right now. Now, if I go with a flat seat, how well does it work to mount the battery on the swing arm, could there be consequences to doing that?

Last thing, this is the first time I have heard the term "bum-stop" cafe style. Minor differences from the standard cafe style?

Thanks again!

[seestheday]

I doubt you will get nearly enough by selling the stock carbs to get mikuni's.  Maybe if you are able to fab your own manifolds and find two used mikuni carbs that will work.

I suppose you could always check ebay yourself though.

[seestheday]

One other thing to consider, depending on how much performance you want, is riding this with the stock carbs and pods.

The cb750c guys will tell you that the bike runs like poo with them, but the deuces wild guys say it will run fine.

Based on the racing experience of the cb750c and cb1100f sites, I'd say that if you want peak performance, then pods on the stock carbs aren't the way to go.

If you want a bike that is more for just cruising around then you should be able to get away with them.  That said, I haven't done it, so you'll have to make up your own mind what you want to do.

[Hoosier Daddy]

A "Bum Stop" is a Brit term for that style of seat. Where the Cafe's started... The seat hump stops yer bum from sliding off the bike. Seestheday has a great point. If you want a dependable, road worthy bike with the least amount of hassle, keep the stock carbs and airbox. Some never do get them to run well with pods. Some say they got them to run "fine" but "right" is a different thing. For the record, I am keeping mine with stock induction system. And nothin wrong with a Cafe' and side covers.

[Larry spillman]

There is little you can cut off the frame most unnecessary items will be for seat and seat lock, once you know what tank you will use and have that and new seat inplace you will see what you dont need.
As for value of Used clean carbs about $100.00 on Ebay or Craigslist.If your carb rebuild goes well you wont need any other carbs.