18MM Mikuni Carb

Discussion in 'Performance Mods' started by misteright1_99, Jul 5, 2008.

  1. I bought a used 18mm Mikuni carb from a 70's Yamaha 80cc dirtbike and installed it on my 48cc HT engine. The carb was a direct fit right down to the clamp on type of mount to the intake manifold. The throttle cable fit the replacement carb as well with no modifications. I did have to lengthen the fuel line, as the inlet is on the opposite side in the Mikuni. Because of the style bike I decided to make an air filter assy. on a 90 degree turn. It runs much smoother than the stock carb (no surprise), I am however waiting on some smaller pilot jets as the ones in it are way too large. When I get the jets instaled and know the sizes I will post the Pilot, and Main jet sizes, as well as the air screw adjustment. Here are a few pics.......

    Attached Files:

  2. badmoon

    badmoon Member

    very nice .
  3. fastboy9

    fastboy9 Member

  4. Well I think I am finally close to having the carb dialed in. It has been raining here forever it seems, and took even longer to get the jets. It runs very smooth, and I think I could go one size larger on the main but here is what I have...

    Pilot Jet is a 25 (I believe it could use one size smaller a 20 but I didnt order it lol)
    Main Jet is a 80 (Again one larger would probably work, But I didnt order it)
    Needle setting I had to groove needle to lean it out I believe because of the 25 pilot jet
    Air Screw setting here in Florida 1-1/2 turns out seems best.
    I am running a NGK B6HS gapped at .028

    I hope this will give anyone that is going to try the Mikuni a baseline to start with...
  5. I love that you can control the choke with your left hand while your right hand is on the gas. That's the way it should have been from the get go.
  6. Have to hand it to the Japanese.........
  7. mcassMB6

    mcassMB6 Member

    If I have a 67cc Heunsheung Chinese HT engine, do I need an 18mm Mikuni? I've seen other sizes on ebay such as 24 and 32mm.

    Where might I find a carb like this?
  8. I have read posts stating mikuni 22mm works good. I believe that would be very hard to jet. I am satisified with the 18mm, maybe 16mm would be better and easier to jet, but I got a deal and it mounted the way I wanted..

    I got mine off Ebay......
  9. arceeguy

    arceeguy Active Member

    I agree, I think going bigger than 18mm on a 67cc engine would not net any more power, and will result in unacceptable low-mid range even after you dial in the high speed jetting. The new 24 and 32mm carbs on eBay are meant for 150-250cc 4 stroke motorcycles and scooters. My little 110cc 4 stroke motorcycle has a 20mm carb.
  10. datz510

    datz510 Member

    Wow!!! Thanks for the info on these Mikuni carbs guys.. I'm gonna have to go snag one off ebay for my own bike now. These look to be the carb the chinese duplicated for the HT engine.

    Once you got your carb and started tuning it, where did you get the different jets from?

    I tell ya what.. high end carb, sick shifter kit.. these bikes have come a long way in just a few months.
  11. datz510

    datz510 Member

    Looking aroudn online, apparently there are a LOT of small carbs we could use on thse engines:

    Vespa's use Dellorto carbs
  12. Ozi

    Ozi Member

    Hey guys,

    Scroll down to Z31 - http://zbox.com.au/spares.htm

    I've emailed Warren with some questions re: the carb ...Looks like a mikuni
    He hasn't responded yet

  13. grezm0nkey

    grezm0nkey Member

    just curious to ask if anyone used this setup long enough to notice fuel used. is it more, or less. another thing, would you want to add a booster bottle?

  14. Boomer

    Boomer New Member

    I was wondering if it would be available in the US as I see he's located in Australia.
  15. djase10

    djase10 Guest

    Hi All
    Excellent thread,
    cheers misteright1_99
  16. Jase, Here is a cool video that you might be interested in, from one of your mates, running a Zbox engine with 18mm mikuni carbi...
  17. fastboy9

    fastboy9 Member

    cool sounds good, have you got the link?
  18. fetor56

    fetor56 Guest

    "cool video"?
  19. Glenn M

    Glenn M New Member

    Last edited: Nov 12, 2008