28mm Mikunis Better Than 29mm Smoothbores?

No eBay APP ID and/or Cert ID defined in Kunena configurationSo there is an eBay listing for a set of 28mm pumpers that the seller claims are higher performance than the 29mm smoothbores. Can this be true? I have never heard this before, but he got the information from "the internet" so it has to be true, right?



Immaculate vm28mm pumper carburetors refurbished. Nicest set I personally have seen, and are better than new , very nice outer chrome bowls and tops. Jetted with 17.5 pilots and 117.5 mains for 4 into one exhaust.New orings throughout and bench synchronized.Very very rare set with the idle adjustment at the top as well as 2 fuel inlets, with double diaphragm pumper on #2 carb.You won't find these anywhere. From the research and reading I have done these out perform 29mm smoothbores when it comes to racing, kz forums. Don't take my word, Google it.see below ...

Mikuni made another mistake with their 29mm smoothbores. Remember the smoothbore insert that supposedly allowed more air to flow through the carb, than the OEM 26mm carbs. Well, it turns out that the insert actually killed low speed jet signals, reducing low and mid range performance. Some people would call it a flat spot. In our drag strip tests we found that an OEM 28mm carb (Z-1 or Z-1R) actually outperformed the 29s at the drag strip. The 29s flowed more wide open, but the 28s has better low and mid range mixture control, power, and that is what wins races.

So are these these stock Z1-R carbs? I don't think the other ones I've had were pumpers though....

Looking at these again....they're just regular 28mm pumpers from the '79 and '80 1000's, right?

It is a known fact that they do have a problem just off idle but "most" of it can and has be worked out with jetting and adjustment..... mine always has but for mid and high range power I think they would still out perform the 28s.... not by much but I'd put my money on the SB exspecally at 650 a set...... Can't wait for more experienced folks to chime in as I'm probably gonna put mine back on this year and need a little advice on improving the just off idle hesitation.

Those are the carbs that came on my bike, so I guess I only paid $850 for the rest of the bike with Lester mags

I have no experience of which is better, but I don't see how a set of carbs like that could be worth $650.

If you are doing a restore I could see the $650. If not the money is better spent on a set of new CR carbs.

Hard to beat AP's on a carb set none-the-less on most app's, street, strip or otherwise when it comes to the complete range.

I have heard good things about the 28's witht he acc. pump. IMHO all carbs should have an Acc. Pump. It just makes good sens. They used that on cars why not bikes. As for the 29 Smoothbores they are fantastic carbs. We have used them on a 550 withonly slight low rpm hesitation and on the KZ 1000 race bike . They need very little tuning to make work really good. If you have to replace or adjust the needle they are a bit of a pain in the ass but usually you dont have to mess with the needles. The CR specials look fantastic and are easy to work on esp. in regards to the needles. Thank god becasue they never seem to run the way you expect from factory. They often require alot of tinkering to get them to run right.
ei. On my 1983 KZ 750 superbike w 31mm CRs I went from the stock 125 main to 105 and I went two sizes leaner on the needle. It took hours to get it to perform well. Pulls really good now.

There's a very good Japanese mechanic working about an hour from me that said the 29's are much better carbs over all. He said the '79 / '80 28's are very hard to tune. I'm just not sure if the ones listed are actually the regular '79 / '80 variety or something special? Seller states there aren't many around and the 28 pumpers are pretty common.

Variations of opinions from mechanic to mechanic on virtually any subject known to man can literally fill hundreds of forum pages regardless of subject. Hard to beat your own experiences, given the opportunity and resources to do so. However various experiences from rider to rider is the beauty of these forums, and can give food for thought from many different angles. Won't be long and you'll be doin' 75mph wheelies up n down the nearest Interstate Hwy! ..................................Mike

Vroom-vroom!

79MKII wrote: Looking at these again....they're just regular 28mm pumpers from the '79 and '80 1000's, right?

Yes! that's all they are. They were on Mark II's also. Just the start of "tree huggingness" for the EPA Liberals! Factory had to lean out the motorcycles to pass emission tests to enter the USA. Don't forget about the smog head also for the Mark II's at the same time.
That's why these 1000cc OEM bikes came with only 105 or 107.5 main jets. The accelerator pump gave it a little blast of gas for throttle response. Too bad, I trashed a couple over the years, I was too cheap to buy the rebuild kit for the pump.
They are just very nice stock carbs. Nice for a correct restoration. I would only pay 1/2 the $$ maybe? If I even needed them.
That's my 2 cents worth.

Started out new in 78 with 26mm on my LTD My LTD would out pull down low my best friends 78 Z1R with 28mm stock carbs then he would start pulling on me and win everytime... 1/4 mile runs
I went to 29mm SB carbs and now could beat him every time. These 2 bikes repeated these races at least 1000 times
Then he added a Winning Header and he was now dead even every time.
I then added a Yoshimura pipe to my bike and was again the winner every time
Both to this point had stock motors. so carbs and pipes were only variables.
Hope this helps
Dave