Mikuni carb for 100cc

[Tommy Ellis]

Can anyone recommend which Mikuni carb I can use on my 74 Berkshire?
My engine is a spigot mount so I'm guessing I need an adaptor? Also any help on jetting would be helpful. Thanks

[Ron]

Tommy,
If your going to ride any of the AHRMA events they have a 28mm size limitation for 100cc bikes.
RonW

[Ernie Phillips]

Tommy,  Welcome to the POG.  We are running a 28mm Mikuni on a 72 Berkshire.  Jetting is 160 main, 45 pilot, 169N-8 needle jet, 5F21 needle, 2.5 slide.    This has been good for stock motor riding sea level to 2-3000 ft.   Mounting is via rubber hose & 2 hose clamps.  The cylinder spigot is 33mm diameter.  Visit your auto parts guy with carb in hand and he should be able to fix you up.  You have to either push back the air boot or cut one ring off to get the carb to fit in due to the two male spigots mounting end-to-end. Since replacement air boots are $50 a pop, we did not cut the boot.  It is a tight squeeze.   We also run this carb on 125s and jet accordingly.  If you can get a Bing in good condition, disregard all of the above.  Our best running German engines (Sachs & Maico) have Bings installed and give superior performance.   Bringing a 30+ year old Bing back into shape may not be cheap, so Mikuni is a good option sometimes.  And, in case of a spill, the Mikuni seems to be easier to re-start. See photo & Jetting linked below:

http://s250.photobucket.com/albums/gg276/ernie7711/?action=view¤t=penton44u100cc062-1-1.jpg

http://s250.photobucket.com/albums/gg276/ernie7711/?action=view¤t=jetting5-13-08.jpg

jetting chart is for 125 except highlighted in yellow =100cc



Ernie P.
Chattanooga, TN

[smkt342]

$50 a pop!  where are you sourcing those things?

Keith

[Dwight Rudder]

New 28mm Mikuni are hard to find as they have been discontinued. The 26mm should be fine for a 100cc engine and most 125cc engines. I believe that many people over carb their bikes.
IMO,
DR

[Ernie Phillips]

Keith,

source:  Al Buehner

RUBBER AIR BOX BOOT
fits all 1972-76 bikes with fiberglass air box to Bing Carb
#51-06-026-200 -  $ 49 each

Do you have another source?  Thanks -



Ernie P.
Chattanooga, TN

[Tommy Ellis]

Thanks for the great information. I'm guessing that finding a bing in good condition is a difficult proposition? I'm restoring this bike and I'd love to find a NOS, but I want to ride it so a good reliable carb is the reason I was asking about the Mikuni.

[smkt342]

No, no other source.  Didn't know they cost that much just surprised me.

Keith

[john durrill]

Tommy,
 There are some 27 mm Bings out their . Ask the folks in the group.
 Someone that has gone to a Mikuni could have one on the shelf .
 If you want an NOS carb here is a shortcut to a man that has the 26 mm body http://www.genuinenos.com/
 Bing international may still sell the type 53 new.
 I would find a used one off ebay or from the group and rebuild it.
 That is the carb we use and they work like new when rebuilt. You would need a new slide , new float ( the new black ones are better with modern fuels ), new float needle seat and needle , new needle jet and a choke piston probably . It does add up but when its done you have the jetting for that carb already available. It works and the bike will run good  from the start. It fits the air boot and cylinder. The stock throttle cable and choke , enricher cable fits both the carb and the controls.
 For us it was a lot better than having to work out the right needle , needle jet combo and which slide cutaway works best . Main jets are not hard to figure nor the pilot jets But it does involve buying a lot of extra jets , pilot , needle ,main and a few needles and maybe a slide or 2 to get the Mikuni right. This runs the cost up quick on the Mikuni.
  Bing , 27 mm type 53 stock on a Penton 125 B engine
 140 or 145 main jet ( all this depends on how hard you ride , the type air filter and what fuel oil mix you use )
 276 needle jet
 40 , 45 pilot jet
 B slide
 #4 jet needle
 Hope this does help,
 John D.