Factory carbs swapped for single Mikuni ???

[shinyribs]

Hello guys,newbie here and first time ever working on a bike.  I just picked up a 1976 cb750(F...?) super sport. My Dad used to own a bunch of these in back when he was buying off the showroom floor. Im in the process of getting this one up and running. Anyway,my Dad was telling me the other night that he had one bike that he replaced the factory carbs with a single Mikuni and that it was one the best running bikes he ever had because of that.   I was wondering if anyone had any insight or opinions on this swap. Figured if it was a worthwhile/feasible idea i would go that route other than try to mess with the crud i got   Thank you for any and all ideas!!!

[TOOLS1]

I have been wanting to do a single carb CB 750, for some time now. I would like to know how your Dad did it. Did he buy a kit, or do it himself? I found this video on you tube awhile back. http://www.youtube.com/watch?v=Ae2HO_I0aVI check it out.
TOOLS

[shinyribs]

hey tools   he said it was a kit   but it was also something he did when the bike was new   so who knows about back then

[shinyribs]

cool video   what a set of handlebars!!!  i got about a dozen of those old two barrel rochester laying around      i never throw out anything       seems like a bad place to have a carb though     and good backfire and it'll make your babaies come out naked!!!

[shinyribs]

Hey tools i was wrong about it being a kit       one of the mechanic at the dealership was making them himself and selling them so it was a one off type deal after all      Sorry if i got your hopes up!!!

[TOOLS1]

OK, Now go find the guy.
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[shinyribs]

HAHA   man,i cant even make a bike run and you want me to build a time machine??  Sounds fun lets do it....with a single carb though

[TOOLS1]

I think Cabreco  is all ready working on a time machine. Only problem is, he is using a CB 750, and not a DeLorain.
Can your Dad describe any details of the manifold? Size, shape, materials, or layout?
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[shinyribs]

He didnt mention anything about what it was made out of,but he did say that it sat centered under the seat and had an air cleaner on it     i'll look thru some old photos and see if im lucky enough to find a pic of one    of course if i do i wouldnt know how to post it         i'll see what i can find

[phil]

Here is my 2 cents ( it might not even be worth that)
cycle x builds and sells a 2 carb set up for cb750's. O.K. so that's only half way there. But, my thought is that
the single carb is the easy part and makes some sense. The hard part is the intake manifold???
So if you start with a facsimile of cyclex's 2 manifold set up and then join them, might that not work? then of course you'll need to calculate the intake volume of the 4 stock carbs and jet the new single accordingly.

[shinyribs]

I agree Phil     anyone know the cfm ratings of the factory setup?    Didnt Volkswagen or Corvairs use some side-draft stuff?  I bet there is an easy swap somewhere       As far as the manifold,the hardest part,i think would be getting all four runners even in length and pacgaking it under the seat without severe bends       other than that it just some exhaust tubing (stainless steel,of course) a tubing bender an some wleding    i wanna do this    just need to find a suitable carburetor   it out there

[TOOLS1]

The Cycle-X two carb set up is great. i have several friends who have them, but they will not fit a stock frame, and I just want to be different.
TOOLS

[Lucky 1]

There is a much better 4 into 1 system available
 and there is a video on Youtube showing how well it runs.

[Lucky 1]

The Cycle-X two carb system seems to work well.

[Hoosier Daddy]

Corvairs ande V.W.s used downdrafts. Had a 66 'Vair once
Might I suggest a side draft Weber DCOE?



 Seems it would be easier than adapting a downdraft like an old Rochester "dual-jet" and dealing with the 90 turn.

 Fab up a manifold something like this and you wouldn't have near the headache of eqalizing the individual runner length.

[Lucky 1]

The bottom photo of the intake manifold would work but the end of the large tube
must be smaller opposite of the end where the carb mounts.

It needs to be a divergent duct, to increase the velocity of the
 air for the cylinder farthest away from the carb.

Look at the similar ones created by the large car companies.

[shinyribs]

Hoosier,if I took the time to fab up that manifold I'd be tempted to hang a turbo somewhere

[cdaiscool]

I like the way you think.

On the other hand, I wonder how difficult a supercharger would be. Hmm. Since there's no belts direct off the motor, probably nearly impossible. But the whine of a supercharger would scare the crap out of most competition...

[Hoosier Daddy]

Lucky 1 wrote

The bottom photo of the intake manifold would work but the end of the large tube
must be smaller opposite of the end where the carb mounts.

It needs to be a divergent duct, to increase the velocity of the
 air for the cylinder farthest away from the carb.

Look at the similar ones created by the large car companies.

Both ends of the tube would be closed and the carb centered, on the rear, acting as a plenum...that should help ensure flow to each the short runners is equalized. If you notice, the individual runners are angle towards the center. Thats why I chose that pic, so you could see the inards... but you are right Lucky 1, tapered down to both ends would be ideal.

shinyribs wrote

Hoosier,if I took the time to fab up that manifold I'd be tempted to hang a turbo somewhere

Now yer talkin... there is, after all, a method to our madness.