Topic: 750 roundtops on 550... who’s running them ?

[bleach8484]

I'm looking for a little first had experience here. Is anyone currently running them past or present? Would you choose them over standard cb550 carbs? What about roundtops vs cr26?

I’m going pretty balls out on my motor (didn’t plan to go this route, just kinda happened). I picked up a set of round tips from Mr. Benton a while back when I had plans of just doing a cam. Now the motors getting a MR stage 3 head, oversized valves. Cam. 600cc big bore. And lightened and balanced crank and rods.

I imagine the carbs should handle this setup just fine, but CR26’s are tempting. I already had them mocked up and they fit on the head just fine. They run a throttle dual cable  just like my GsXR switchgear, so all that’s fine.

[Bankerdanny]

Those sure are pretty. If they fit spacing wise I don't know why you wouldn't use them unless the CR's are much easier to tune.

[bleach8484]

Spacing and fitments all good. I’m sure either will suck to tune for me since it’s my first carb bike 

[seanbarney41]

Roundtops are the sledge hammer of the motorcycle carb world, super durable, and easy to work on.  It takes 5 minutes to change jets and adjust floats on the bike.  Unfortunately, they do not have a wide range of tuneability.  So, if you can get 'em to run decent, I would think they are a good improvement over the fragile and finicky 550 carbs.

Another possibility would be Mikuni vm series available in throat sizes from 22-33mm, as found on 1970's Kawasaki's and Suzuki's.  Bwaller runs 'em on his 550 race bike so it can be done.  Nearly infinite tuneing combinations because of wayyyyy more parts available than for roundtops.

Cal, Bwaller runs smoothbore 29mm Mikuni's which are known to flow much more air than 28mm roundtops

[bleach8484]

28mm is round top size I believe.

[bleach8484]

I purchased a Dynoman “power pack” sort of deal. 61mm, 10.5 cr and Its a web stage 2 cam, but that’s just sitting brand new in the box... I suppose I can always sell and upgrade if that’s not up to snuff.

I spoke to Mike on the phone today... and he said just give them a shot and see what they do. They pretty enough to where I shouldn’t have a problem getting rid of them if the time comes.

[bleach8484]

"I used them last season on my mildly ported 550,pods,streetable 4inone exh.(classic k style carbs w links)
 125 mains,40 idles,needles in the middle pos.
 used carb runners of k3 model 550,(gave the best spacing)using new 500 intake rubber. Mounted carbs, rubber and runners on workbench(tight fit! but o.k) then fitted complet assy to cylinder head,
 raised tank slighty for clearance(could not bring myself to ding tank!)
 would do 195 km/h on freeway,reving 10k,never quite solved the clearance issues though.
 carburation was VERY sensitive to crosswind/leg position
 great sounding and looking mod.HAVE FUN."

"The old Clymers manual with the performance section even gives a jet recommendation for the 750 carbs on a stock 550..."

I found  a few tidbits of info from very old post. I forgot about dinging the tank, but I have a 500t tank so maybe I'll get lucky and not have to dent it. I wish I had everything here to mock it up again and test fit, but the engines spread out in all corners of the US right now (Atlanta, Cali, and Mass.)