Topic: Honda CB550 Mikuni 29mm smoothbore carbs?

[Terry in Australia]

Ok, I got up nice and early for my first day of winter, but sadly there was no snow, so mildly disappointed, I trudged out to my garage to continue with the adapters. Apart from trimming them down a tad, everything went like clockwork and the carbs are on!

I still need to strip the carbs and give them a thorough cleaning after the PO washed them with God-knows-what and they leaked black water all the way from the US to Oz, but the slides are all unstuck as are the choke linkages, so I don't think it's gonna be much of a hassle.

Here are some more pics. Cheers, Terry.

[troppo]

Pretty slick work there terry, love those trumpets, you spin them up yourself?

[Terry in Australia]

G'Day trop, thanks for that, no, I bought those trumpets about 4 years ago when another bloke was gonna send me a set on Mikuni 29mm smoothies, but I think he forgot? Ha ha, oh well, better late than never! Cheers, Terry.

[FunJimmy]

76-77 Kawasaki KZ1000's had Mikuni vm26mm carbs and they are readily available on feebay.
Would these Mikuni carbs be an improvement to a mildly modified CB550?
I'm building up a 503 kit using Yosh high comp (not excessively) pistons, cam and head port work.

The KZ carbs look like they use standard Mikuni screw in jets, which should offer greater availability.

Would it be worth the work that Terry has done to graft these carbs on to my café project?

Thanks
Jimmy

[MRieck]

Ha ha, thanks Trop, it was a bit of work, but once I made sure it was right, the other three didn't take long at all! Cheers, Terry.

The learning curve is steep brother.

[Terry in Australia]

Ha ha, thanks Trop, it was a bit of work, but once I made sure it was right, the other three didn't take long at all! Cheers, Terry.

The learning curve is steep brother.

Ha ha, that's right Mike, but it's a great way to spend a weekend!

76-77 Kawasaki KZ1000's had Mikuni vm26mm carbs and they are readily available on feebay.
Would these Mikuni carbs be an improvement to a mildly modified CB550?
I'm building up a 503 kit using Yosh high comp (not excessively) pistons, cam and head port work.

The KZ carbs look like they use standard Mikuni screw in jets, which should offer greater availability.

Would it be worth the work that Terry has done to graft these carbs on to my café project?

Thanks
Jimmy

I'd go for at least 28mm carbs mate, if you go back a couple of posts, Turboguzzi has some pics of a pretty neat conversion. 28's are a bit harder to find because the Kz owners grab 'em whenever they can, but a good set of 28's with some of Mike's head work and a decent cam and you'll be chopping up 750's! Cheers, Terry.

[bwaller]

FunJimmy,

I can tell you first hand bigger carbs are needed to finish the package. Terry's probably right on with the 28's in order to stay "streetable" and still deliver enough air. 

The Yoshimura 500 full balls race bikes used 31mm CR's!

[FunJimmy]

Ya 28mm Mikuni’s don't seem to come up very often.
The little 550 came stock with 22mm carbs.
Won't the 26mm Mikuni’s be a considerable improvement?


FJ

[bwaller]

Absolutely!

[mlinder]

You need to make sure that your bike is pulling enough vacuum to warrant very large carbs. It's easy to over-carb just about anything.
I believe Paulages race 550 is running vm28's, but that thing is far from stock. Not very stock at all, I reckon.
The kz650 uses vm24's, which I daresay pulls a bit more volume through than a mildly breathed on cb550, and it doesn't seem terribly under-carbed to me.

[Terry in Australia]

Ya 28mm Mikuni’s don't seem to come up very often.
The little 550 came stock with 22mm carbs.
Won't the 26mm Mikuni’s be a considerable improvement?
FJ

26mm carbs will be fine mate, get some! Cheers, Terry.

[turboguzzi]

hei Fun jimmy

dont know if my carbs are called 26 or 28 VM as the actual throat is more like 27.... in any case, they work great on my bike with a megacycle 126-20 cam.

did one endurance race on a friend's CB500 with CR31's and didnt like the way they worked, very on-off. mine pulls much better from mid range, so I'd say they are a pretty good match for a hot 500 with port work. 

my 0.02

TG

[FunJimmy]

Turbo

Thanks for the endorsement! I’d like to give them a try, but I’m finding it difficult to get fitment information. My understanding is that the Kawasaki carb spacing is quite a bit different than the Honda spacing, especially the little 550. How have you fit them on your bike?

Cheers
Jimmy

[turboguzzi]

well, the original 500-550 carb spacing is indeed quite bad for performance, all manifolds have that S shape which cant help HP.

look at the pic i posted in page 2, the GS750 carbs I used have about 100mm between central carbs, 75 between the external ones and it matches the 500 head really nice.

all you have to build are ally adapter similar to those terry did and simply bolt the flnage directly to the head. I even manged to use the original 500 rubbers.  it's true that the outer carbs stick out, so you'll have to scrap the air box and use single pods for street riding.

A mechanic friend of mine actually went all the way and built a new fiberglass airbox! If you are interested, could ask if he would be willing to do another one.

will post a shot of how these fit to my bike later on.

Cheers
TG

[FunJimmy]

The GS750 carbs I used have about 100mm between central carbs, 75 between the external ones and it matches the 500 head really nice.

TG

I see what you mean. My 550 intake port spacing is exactly that!
Where did you get you manifolds?
My guess is you made them, and I will have to as well.
Could you post pictures of the manifolds too?

If you mechanic friend would be interested in making a airbox or selling the mold, I'd be interested.

Does the KZ and GS have the same spacing?

Thanks
FJ

[Terry in Australia]

Does the KZ and GS have the same spacing?

Thanks
FJ

Yeah mate, and there are 28's and 26's on EBay now.

[paulages]

been on tour for a couple weeks, so i couldn't reply often... my 550 racebike has custom made runners to fit to the VMs. the spacing is definitely a big improvement. i can't find any good pictures, so i'll get some when i can if that would help anyone.

[FunJimmy]

That would be great Paul.
Are you using GS or KZ carbs?

FJ

[paulages]

That would be great Paul.
Are you using GS or KZ carbs?

FJ

KZ. i was told they were off of a Z1.

[turboguzzi]

jimmy

here are some close ups.

as you can see the outside carbs stick out of the frame tubes, not really a problem in a racer but not so nice on a street bike.

take into account that the carb spacing doesnt exactly match the ports in the head so the manifolds have to be slightly angled.

I tilted the carbs down for some downdraft effect, guess that even if you keep them level, you'll have to change the push pull cable bracket like I did (last pic) as it will hit the frame

hope it helps

TG

[FunJimmy]

Thanks TG

Those pictures will be a big help.

Cheers
Jimmy

[Dunstall_74]

Just installed a rack of VM29 smoothbores on my CB750 today.  I used the intake boots that dynoman sells specifically for this application. http://www.dynoman.net/bikepages/sohc/carbs.html#InMani.  Only thing I had to do different was use standard hose clamps (boot to head), I stayed with Honda oe clamps when mounting the carbs to the boots.  Feels good and firm.  Now, I'm just waiting for my K&N filters to arrive.  Hopefully have it running by tomorrow.  Paulages has a set on his 550 racer. I went over to his shop the other day to listen to it run....OH What a Screamer!  That has got to be the meanest sounding 550 I've ever heard. 

[FunJimmy]

Are there any issues with the cable linkages?
Frame clearance or cable routing etc?

[turboguzzi]

hey dunstall. any idea on what bike were those carbs originally mounted?

Just so I know what to search for.....

Thanks

TG

[Dunstall_74]

hey dunstall. any idea on what bike were those carbs originally mounted?

Just so I know what to search for.....

Thanks

TG

I'm pretty sure they came on '73-76 KZ 900 (Z1) and pre 1980 Suzuki GS models.   They may have come on some others as well.  FYI, I got the K&N Filters(Part #RC-2454)and the carbs perform great.  Definitely an upgrade from the stock Keihins.