Rejetting the mikuni 30mm carb on the Lifan 140.

Find deals on amazon
Shop deals on ebay
Advertise with us
Mini Dirt Bikes & Pit Bikes Forum

Help Support Mini Dirt Bikes & Pit Bikes Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
motoluver

motoluver

Well-Known Member
Joined
Mar 7, 2007
Messages
1,223
Reaction score
1
Location
Newcastle
Hey everyone, I am pretty sure that my lifan 140 is running rich, when you crack the throttle it will sometime's try to die like it is getting to much fuel in the motor. And also when going around berms and you open the throttle up it sounds like it's getting to much fuel and you have to wait a couple of seconds until it starts revving out. I am guessing that the Mikuni 30mm carbs what come stock with the Lifan 140 are not genuine Mikuni, but can you still use Mikuni jet's in them??? Has anyone jetted one of these carbs for your 140? What size jet's should i change to. Also another thing what can be contributing to my problem is the stock air filter, it's much thinker than a Uni filter and doesnt breathe as good as a uni. So I am going to get a uni filter for it as well that could be the reason why the motor is getting to much fuel??? Also i have a feeling that i have been running the engine on reserve this whole time as the fuel tap is weird and i ran out of fuel today coming home. I tipped the bike over so the remaining fuel what was in the right hand side of the tank went into the left hand side, i then tried switching it to reserve but it wouldn't start so i put it back to the "on" position and it started. So another question does running an engine on reserve use more fuel??? Because this 140 is a real petrol guzzler compared to my Ducar 125...
All opinions are appreciated. And i also wouldnt mind saving up and buying a Keihen carb. I have never been a fan of Mikuni they are junk imo.
 
When your bikes not warmed up those things are normal, I'd say its fine but if you feel its not then investigate further, check the colour of the spark plug, if its charcoal black then its running rich, it should be light brown.
 
Flarry said:
When your bikes not warmed up those things are normal, I'd say its fine but if you feel its not then investigate further, check the colour of the spark plug, if its charcoal black then its running rich, it should be light brown.
Click to expand...

I dont ride and of my bikes when they are cold that's just dumb. This is when riding when the motor is at normal operating temperature. I just gave it a wash and noticed a very tiny arrow on the fuel tap lever... Yep I have been running my bike on reserve this whole time lmao. I will first buy a uni air filter, clean the spark plug, adjust the gap if it needs to be done and ride the bike with the fuel tap on the "on"position lmao. If it still doesnt ride at it's full potential then i think it will be time to re jet. Anyone know if running a engine on reserve can result in the issues i described?
 
Riding your bike with the fuel on reserve makes no difference, all the difference between "on" and "res" is that the res pick-up is a little bit lower in the tank on res, it basically is just a warning for you to get more fuel as ur nearly empty, gives u about 200-300ml, just enough to get back to fuel up!!!
also being a 30ml mikuni on a 140cc, of course ur gunna use a shit load more juice.......
 
if the uni filter doesn't work don't change the jets just move the needle down one or two notches or screw the fuel mixture screw in a little and then check the plug and if it needs to be running leaner change it some more. Most people i know are trying to get the most out of the carbi's so i wouldn't be changing jets just yet. worst comes to worst take it to the motorbike repair shop and get them to tune your carbi for racing, it will feel heaps better and doesn't cost much.
 
Yeah im with pegleg riding your bike with the fuel on reserve makes no difference. With the carby try changing needle positions and then maybe try getting different jets i would take in your ones from your carb to a bike shop and see if they have same sort of jets i would say they will
 
Yeah thanks guys. The first thing I will do is put a Uni filter one as the stock on is restricting air flow. The Uni filter will be my starting point.
 
motoluver said:
I dont ride and of my bikes when they are cold that's just dumb.
Click to expand...

no its not, you should always warm the engine up by riding it not letting it idle for 25 minutes till its red hot...

i found putting more fuel in cured the issue of dying with too much throttle, so i would play with the needle first.. try going richer first, and if it helps the top end in the slightest (even if the midrange is worse) then you need a bigger main jet... yes mikuni jets will fit, just take a sample to your local bike shop and they'll give you what ever size you need.

is your filter one of the "dual stage" ones with the sleeve around the outside? i took the sleeve off and it seems to breath really well... just make sure shes clean and oiled. but grab a uni if you want
 
Riding a cold engine can risk breaking the con rod bearing and premature engine wear. Start your motor, rev it for a good couple of minutes and then take it easy for another couple of minutes until its fully warm. Also letting 4 strokes sit ad idle while cause them to overheat.
 
Hey Motoluver,you are right about the '30mm' mikuni's being rich,but only at idle you will find.
The pilot jet will be a No.20 and adjusting the mixture screw won't make any difference,you need to run a No.15 like the 22-26mm carb's,run the mixture screw 2 turn's out from closed and for the main jet run a No.105 with the needle clip in the middle.
This state of tune will get you in the ball park but you will need to fine tune this to suit your riding style/preference,I have set my own Pit Pro and 2 other's with these Carb/Motor combo's and it give's a nice snappy throttle and strong mid to top end power,Hope this help's!
 
the motoshop put a 105 main jet in my agb29 and it was really good when it was cold. i went to southmorang pit bike track last friday and it was running to rich like when i gave it gas it would like die then i hate to wait abit till i could full throttle i took the sparkplug out and it was DARK DARK black so i took the bike back to the motoshop and they said it was running to rich and that the fuel filter was up side down and the fuel was just driping in. so they fixed it and now its running good as. i want to put a 105 main in my avenger cause it gave me heaps more topend speed and so forth.

thanks
 
Yeah Quick-Prox,it's a problem with most pit bike's that they run a little rich at idle and lean up top.
The 105 main jet is the cure for 125 motor's!!!
 
Is a 105 main jet suitable for a 125 Lifan? as my bike dies if you snap the throttle open. I have changed the E clip and it didnt make a big difference.
 
my bros bike is runing a little rich at idle and lean up top. how do i fix can i just put the idle down would that help?
 
cass38a/Quick-Prox, the 105 main jet is fine on 125 motor's(lifan,Ducar etc.) and the pilot jet is usaully a No.15 and is fine.
If it's running rich at idle you need to adjust the mixture screw,which is located underneath the carb towards the manifold.
I recommend the 105 main jet/15 pilot to both of you with the clip on the middle of the needle and tune the mixture screw....this should fix all your prob's and more.
 
Hey Toddo thanks for your input. I will give the 105 a go next time when I go past a shop.
 
Sorry Quick-Prox,i thought you had the 105 main.
Try putting the clip on the bottom and go for a blast,if it feel's a bit better then you could go for the 105 with the clip in the middle or even 1 down from that.
Cheer's motoluver,just remember with any mod's carried out on carb's you must tune,tune,tune,pain in the butt and time consuming but worth it in the end,more power,easy starting and longer engine life.
 
You must log in or register to reply here.

Latest posts

Back
Top