intake size

try the long z intake it has a 16mm ID bore. i think the vm 16 has a plastic spacer to make it the same as the china girl carb but i am not shure

i am also running a 16mm carb too and love it !!! its just the right size for a modded motor !!! not so big you loose intake velosity through the venturi and not so small it suffocates the motor, it would seem 16mm is just the right size for all aroud performace when you have a well modded motor, the 18mm will breath better yeh but at the cost of lower velosity flow through the venturi and that leads to a soggy low end and loss of power at low rpms.

now you will need to run an intake with a 16mm inner diamiter boar ! if you go smaller on the bore of the intake than the bore of the carb you will restrict the carb ! 16mm carb requires a 16mm intake bore for best performance !

i rtied using the stock shorty but it was only 13mm and it was terrible !!!! 4 stroking gallor !!! the carb was way to restricted, but when i swapped out to a longer intake with a mutch larger inner bore the motor came to life !

16mm Mikuni has a 21mm I.D. at the intake side.

Within a few millimeters of inner diameter from the ideal size it is only a myth that larger carburetors cause worse performance at low RPM. It is just a matter of jetting them correctly.

Here a few spacers. Good luck!
https://www.treatland.tv/SearchResults.asp?Search=carb+spacer

48ccbiker said:

16mm Mikuni has a 21mm I.D. at the intake side.

Within a few millimeters of inner diameter from the ideal size it is only a myth that larger carburetors cause worse performance at low RPM. It is just a matter of jetting them correctly.

Click to expand...

Yup that myth sticks to a lot of people lol. If you want a large carb you need to remember your motor can only suck so much fuel so with a smaller carb the fuel get sucked faster through the smaler venturi but with a verry large carb the venturi may be so large that the volume of air floewin into the motor slows down dramaticly making it harder to draw fuel up the main jet due to a loss of negitive pressure, to combat this one may need to go way big on the main jet to make the fuel easyer to draw. So even though the size of the po rt s and te amount of air thr motor can flow stays the same magjor rejetting my be required !!!

If one pushes the limmit of how large a carb he or she can use the carb only becomes harder to tune, no perfomace is lossed anywhere thouh once its tuned in fact performace can be gained.

For a 50_70cc motor I stay below 21mm if the motor is limited to 10,000 rpms after 20mm its a biotch to tune.

13 is too small and will limit rpms but give amazing fuel milege and throttle responce in its low rpm range

16_18 is damn near perfect up to 10,000 rpm for street racing to the track

18_21 would be fore high rpm motors with large ports tunedto run at max rpms at.the track most of its life but can run well on the street if jetted properly but imho its not worh the tunning effort

My 70cc dax with a 16mm yzinger carb full port and polish puch high comp head and custom exhaust can keep right up with my 29er with 70cc dax and fred head 5.3cc and a full port with a delorto phgb 21 !!!! Gearing plays a major role too you knoe and a 70cccan only make si mutch power so its,all about were you make and how you use that power

I though of a super duper low power super high mpg motor bie idea before and it consisted of a 70cc dax with a reed conversion and the ports cleaned up wit the proper piston mods for the reed conversion and a 12mm carb tunned to the motor and a free flow air filter, then a tunned pipe with a restrictive stinger and a 3 sped hub on a 29 inch wheel geard to keep the rpms down at a xruise.

I was thinking of a 200mpg build lol