MIKUNI (CHIKUNI) 22MM TUNING PROBLEMS

#22
Some adjusters are fuel screws but if the carb has a pilot jet that fixes the idle fuel feed, then any idle adjustment is for air. (not counting slide height adjuster)
 

delray

Well-Known Member
#23
he is a video that will help explain things maybe little better from a fuel adjustment to a air adjustment carb(idle) and they both have pilots. it would of been nice too if he went into more depth on the pilot jetting. if I am correct one will go up in numbers to enrich and the other will go down in numbers stamp on the pilot? depending where your adjustment is(front or back of the carb)
I have been lucky latey with a 15pilot on my 22mm round carb's but on my 24 flatside the adjustment is on the back side and the pilot numbers are differnent then the 22mm round carb and the size/shape of the 24mm flatsides are much smaller looking too.
 

delray

Well-Known Member
#26
I seem to have better luck with the genuine mikuni....easier to tune for me....only had good luck with one Chinese mikuni...
can you verify that a real 22mm round mikuni uses a small pilot. different then the china mikuni that is much larger(long)
here are couple pic's I found searching. this may help a lot of people when buying the correct parts for there carb. real thing or china carb?
pilot tm.PNG
s-l500.jpg
 
#27
The top pic is a genuine pilot jet.they are shorter....the bottom pic is a Chinese pilot jet...Also as noted in the adjusting instructions if the pilot adjustment screw is in front it’s an air mixture....in the back it regulates fuel....just my interpretation....

still playing with the 26mm on my bronc...it’s a challenge..
 

delray

Well-Known Member
#28
The top pic is a genuine pilot jet.they are shorter....the bottom pic is a Chinese pilot jet...Also as noted in the adjusting instructions if the pilot adjustment screw is in front it’s an air mixture....in the back it regulates fuel....just my interpretation....

still playing with the 26mm on my bronc...it’s a challenge..
interesting...26mm I was thinking of using a 24mm on a stock/cam 10hp with billet rod and very light mods....header,valve springs..etc make only spin up to 4500-4700 rpm's you will have post a thread when you get it tune and running.... thumb1.PNG
 

Li'l Popeye

Well-Known Member
#30
can you verify that a real 22mm round mikuni uses a small pilot. different then the china mikuni that is much larger(long)
here are couple pic's I found searching. this may help a lot of people when buying the correct parts for there carb. real thing or china carb?
View attachment 264272
View attachment 264273
I have several Chikuni's with the lower pic pilot jet.
And the latest Chikuni came with this pilot jet:

It is Keihin N424-74C thread is M5, instead of M4, which the others have. I have ordered 12 (several sizes) of these pilots for $9,99.
I'm not sure about size, but I think 38 Keihin is around 15 Mikuni?
 
#33
For a vast amount of builds a 22mm Chikuni or VM22-133 will be ideal. I found the VM22-133 to be the way easier option as far as tuning as long as you start with a 15-20 pilot and ~130 main jet.
 

delray

Well-Known Member
#34
here is something else that will help with ID your carb from a china mikuni that most of us use on are bike from a real mikuni.
did any you guys notes how bad the air cleaner side was on that china carb. I never seen any of mind look like this before....egg shaped..
 

Li'l Popeye

Well-Known Member
#37
Also just an FYI...mikuni trade Mark is a small “box in a box” which is on all their parts...
Last week I finally received the pilot jets from AliExpress, for my latest Chikuni VM22. I ordered 12pcs "Keihin N424-74C" in different sizes from 30-40 range. It was $9,99 for 12pcs. They fit my latest carb. And it fits.
I also ordered 12 of the Mikuni style pilot jets (the longer ones with M4 thread. Also different sizes in approx. 12.5-25 area. Also $9.99/12pcs.
These pilot jets do have the Mikuni trade mark stamped on them (the box in a box). But for that price, I don't think it's genuine Mikuni?
Currently I'm re-jetting the VM22 carb and I'm confused about the function of the pilot mixture screw. Airscrew or fuelscrew?!
At first it didn't make any rpm difference if I turned it all the way in or out. After I replaced the 38 pilot jet with a 33 pilot jet, the engine rpm's increase slightly if the pilot screw is nearly turned all the way in. So the pilot screw is "starting to function" with the smaller pilot jet installed. If it was an air screw, that wouldn't make any sense.
I will see what happens when I install an even smaller pilot jet. If adjusting the "pilot air/fuel mixture screw" does have a larger effect than it does with the current pilot jet, I'm positive it is a fuelscrew, instead of an air screw.
 
#38
The way I understand it is...on genuine mikuni carbs the AIR screw is in front...on Chinese mikunis the FUEL screw is in the back...so adjustments will be different...and yes I’ve had to install several different jets before the adjustments take effect....I buy all my jets from niche cycle...about $2-3 each
 
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Li'l Popeye

Well-Known Member
#39
The way I understand it is...on genuine mikuni carbs the AIR screw is in front...on Chinese mikunis the FUEL screw is in the back...so adjustments will be different...and yes I’ve had to install several different jets before the adjustments take effect....I buy all my jets from niche cycle...about $2-3 each
My chinese carbs have the screw at the cylinderhead side. Like this one:

Here it's called fuel screw.
https://www.thejunkmanadv.com/how-to-idle-mixture-screw-adjustment.html
If it's turned all the way in it closes the passage, which restricts fuelflow.
 
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