MIKUNI (CHIKUNI) 22MM TUNING PROBLEMS

#1
Hello, My name is mason and i recently purchased a coleman bt200x mini bike

I purchased a mikuni (chikuni) 22mm carburator kit with filter for it and i cant seem to get it tuned correctly......

i have not touched the needle nor have i replaced any jets. I am currently using the stock jets in it and the stock needle setting.

the bike is backfiring really bad. It also doesnt want to idle correctly.... then i noticed i had alot of fuel in my oil.

I am not very knowledgable on carburators... at all....

i currently live in missouri where the elevation is around 460 feet above sea level.

The modification i have already made to the bike are as follows

Governer removed
Torque converter
header and muffler pipe.

i have seen alot of success to these but i cant seem to get it right....

if someone could please help me with my issues i would greatly appreciate it. I am new to all of this as well.
 
#5
There are plenty of guys on Here running Chinese motors and maybe one of them can tell you where to start with the jets...maybe start with a 130 mAin and a15 pilot?? Just a guess on these motors....
 
#6
There are plenty of guys on Here running Chinese motors and maybe one of them can tell you where to start with the jets...maybe start with a 130 mAin and a15 pilot?? Just a guess on these motors....
I have jets on the way, I bought 3 different mains and 3 different pilots. With the 130-15 where should my screws and float be set? That’s the most confusing part to me
 

delray

Well-Known Member
#8
There are plenty of guys on Here running Chinese motors and maybe one of them can tell you where to start with the jets...maybe start with a 130 mAin and a15 pilot?? Just a guess on these motors....
if he is running a stock cam? the jetting is going to be way under 130 main jet. I think the stock 22mm mikuni/clone carb's come with a 95?
 

delray

Well-Known Member
#10
Hello, My name is mason and i recently purchased a coleman bt200x mini bike

I purchased a mikuni (chikuni) 22mm carburator kit with filter for it and i cant seem to get it tuned correctly......

i have not touched the needle nor have i replaced any jets. I am currently using the stock jets in it and the stock needle setting.

the bike is backfiring really bad. It also doesnt want to idle correctly.... then i noticed i had alot of fuel in my oil.

I am not very knowledgable on carburators... at all....

i currently live in missouri where the elevation is around 460 feet above sea level.

The modification i have already made to the bike are as follows

Governer removed
Torque converter
header and muffler pipe.

i have seen alot of success to these but i cant seem to get it right....

if someone could please help me with my issues i would greatly appreciate it. I am new to all of this as well.
stock rod still?
keep the the engine under 5000 or it will break and only rev it up to that on short burst thottles. don't hold it there for a long time or bang....
billet rods are not expensive. cheap insurance for sure.
 

Davis

Well-Known Member
#11
if he is running a stock cam? the jetting is going to be way under 130 main jet. I think the stock 22mm mikuni/clone carb's come with a 95?
Unless you buy one from go power. The one I bought was doing the same thing. When I called them they informed me they take and drill the stock #95 jet to a #130. Whatta pain that was to figure out.
 
#12
Ok so the engine is stock, I’m not sure where to set the idle screw or the air mixture screw. That’s my main issue is idk where the stock location of them were. I messed with it too much. I know it has a 130 main but I’m not sure about pilot yet.

I ride trails not road so I’m never really in high rpm,s so I’m not gonna change the rod until I motor swap. But like I said I’m not very knowledgeable on these so idk where to even set the screws or anytning. So when you explain the float idk what that means.
 

Li'l Popeye

Well-Known Member
#13
Air mixture screw is referred to as a pilot screw in the article.
"If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs."
The pilot screw is at the bottom on engine side (if it is a chinese one). I have mine set at 2 turns out. That is 720 degrees out. So, screw it in, untill it bottoms, then screw back 720 degrees. And start from there. If you screw it out; it enrichens and screw it in; it leans.
There's also a little hole at the engine side of the carburator; air bleed hole. It's positioned under the 22/26mm hole. Do not block it; it is used by the pilot jet in some sort of way.
The idle screw... You mean the slide height adjusting screw? Look through the carburator and see what it does when you screw it in and out. You may want to screw it in untill the slide is 1-2mm up. I'm not sure how far, but I think it's something like that. It's not rocketscience. Put your bike on a stand, so it doesn't take off, when you start it. This screw regulates airflow through carb and idle rpm. While you're looking through your carb; also watch if the needle is moving along with the slide as you fully open it. Or see that the needle is sliding in the brass hole in the bottom. It needs to be in de brass hole.
Did you take a look at your sparkplug? New one installed? How did it look like? Black/wet?
 
#14
Air mixture screw is referred to as a pilot screw in the article.
"If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs."
The pilot screw is at the bottom on engine side (if it is a chinese one). I have mine set at 2 turns out. That is 720 degrees out. So, screw it in, untill it bottoms, then screw back 720 degrees. And start from there. If you screw it out; it enrichens and screw it in; it leans.
There's also a little hole at the engine side of the carburator; air bleed hole. It's positioned under the 22/26mm hole. Do not block it; it is used by the pilot jet in some sort of way.
The idle screw... You mean the slide height adjusting screw? Look through the carburator and see what it does when you screw it in and out. You may want to screw it in untill the slide is 1-2mm up. I'm not sure how far, but I think it's something like that. It's not rocketscience. Put your bike on a stand, so it doesn't take off, when you start it. This screw regulates airflow through carb and idle rpm. While you're looking through your carb; also watch if the needle is moving along with the slide as you fully open it. Or see that the needle is sliding in the brass hole in the bottom. It needs to be in de brass hole.
Did you take a look at your sparkplug? New one installed? How did it look like? Black/wet?
You have it backwards, it is a air bleed and when you open it more air gets mixed with the fuel from the pilot jet. Screwing it in richens mixture screwing out leans it out
 

Li'l Popeye

Well-Known Member
#15
You have it backwards, it is a air bleed and when you open it more air gets mixed with the fuel from the pilot jet. Screwing it in richens mixture screwing out leans it out
Do I? When I read the article it says:
"The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs. "

What is the back- and what is the front side of a carburator in this? I'm confused...
 

SAS289

Well-Known Member
#16
I call one an air screw and the other a fuel screw. Screwing out on an air screw leans, screwing out on a fuel screw richens. You just have to know which one you have. On the stock carbs for these engines have a fuel screw. I would guess the Mikuni's have an air screw. And Ole did call it an air bleed.
 

fistfullabar

Well-Known Member
#18
left mikuni middle runtong right keihin
honda clone honda clone honda xr70
mikuni came on 70cc pit bike that was raced. runtong came off 110cc honda clone engine. the keihin came stock off the honda. while they all look similar. nothing is compatible with each other. try and tune them carbs!!!
20200523_125057.jpg 20200523_125049.jpg 20200523_125040.jpg 20200523_123845.jpg 20200523_123845.jpg
 

Li'l Popeye

Well-Known Member
#20
I call one an air screw and the other a fuel screw. Screwing out on an air screw leans, screwing out on a fuel screw richens. You just have to know which one you have. On the stock carbs for these engines have a fuel screw. I would guess the Mikuni's have an air screw. And Ole did call it an air bleed.
Ole must have it right. It does provide more air to the pilot circuit if screwed out.
 
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