Topic: Talk to me about Mikuni smoothbores

[zoo mob]

Just got a set with a Kawasaki I bought, considering using them on one of my CB750's, what should I know about adapting them? How much power can I gain, what would I need to do to get it to run right, and what other mods should accompany it?
Thanks

[MRieck]

That's a loaded question. I'd start with the mounting. Those aren't racks that can be modified in my experience. Someone here may certainly know more

[MCRider]

Just got a set with a Kawasaki I bought, considering using them on one of my CB750's, what should I know about adapting them? How much power can I gain, what would I need to do to get it to run right, and what other mods should accompany it?
Thanks

I ran the Mikuni 29s on mine. I had an 888cc with a ported head.  Loved them, more power and civility. My memory is that they were very easy to set up, Jets are available, monkey with this and that. Plan to run them again, same motor set up.

But I think the 29s were more like "from" a Suzuki? and the rubber mounting boots are the key. Stock won't line up. Replacements are about $125 I think from Dynoman. When I bot mine they were marketed for a CB750 directly.

So if you can get the Kawis to hang on your motor you'll likely like them. Bigger than 29 without engine mods might be too big. Heck 29s without engine mods might be too big.

[fishhead]

You'll need the carb manifold adaptors to put them on the CB 750.
 
 Heres a link with suggested jetting. The Kaw's 29's work better than the Suz's 29's because of the slide cut out. I beleive the Suz has less cut out on their slides (Suz 29's not shown in link).

http://www.z1enterprises.com/reference/z1-carb-guide.aspx

[MCRider]

You'll need the carb manifold adaptors to put them on the CB 750.
 
 Heres a link with suggested jetting. The Kaw's 29's work better than the Suz's 29's because of the slide cut out. I beleive the Suz has less cut out on their slides (Suz 29's not shown in link).

http://www.z1enterprises.com/reference/z1-carb-guide.aspx

Good info, as I am getting close to cleaning up my 29s for re-install on my project.

Your Z1 reference chart has the cutaway on the Z1 29s and the CB750 29s as the same. My reference to the CB750 carbs being the same as the GS carbs may have been in error. It was just heresay, and likely it was meant that the GS carbs are similar to the CB750 29s.

Since my 29s were marketed to the CB750 specifically and not as GS takeoffs, I should have the better cutaways.

But that begs the question: you say they "work better". In what way? Civility, low, mid, upper power? Or in general?  TIA.

[JohnG]

I bought a set of "29 mm Smoothbore Mikuni's"  back in the 80s for my stock 750F.  The advertised claim was "10% bolt on horsepower gain".  Did not have a dyno to verify.  Paid about $195; I think the going rate was $295 in those days.  Spent a fair amount on jets at the local Kawi dealer who took some pleasure in socking it to a Honda owner...

They went in to the stock manifolds with no modifications.  The only thing I had to do was fiddle with the throttle cables.

I got 4 individual K&N air filters.

The top end performance was great.  For street riding I was never able to resolve the needle to main jet transition.  In other words, if I was on the highway in 5th gear and got on the gas, it stumbled from being too rich.  If I leaned out the needle it was too lean the rest of the time.  If I decreased the main jet to lean things out then the top end was too lean.  Mind you, my tuning skills were hardly the best.

I later used them on a DOHC 750F  for roadracing, with special cast adapters and they were awesome, entire RPM range.

If you go with the 4 K and Ns, a serious tuner later told me, as compared to the stock airbox, you have changed the length and geometry of the intake tract of the motor so you have to be prepared for unexpected results.  For example, the mouth of the carb is effectively wide open instead of having the smooth transition that the air horns of the CB750 air box provide.  He would have gotten some horns out of a Kawi airbox himself.

                         John