Rejetting the mikuni 30mm carb on the Lifan 140.

[Flarry]

Offtopic, KTMKID, I see you find my video hahaha thats my friend saying "fongolo" hehe.

 

[cass38a]

The main jet is located in the bottom of the bowl. Remove the carby and take out the 4 screws holding the base on. The main jet is the big one right in the middle and it should have a 95 printed on it. It also has a slot to remove it with a screwdriver. You have to hold the hex shaped needle jet with a small spanner to remove just the main jet.

Go to this link and you will see a picture of a main Jet (the one you want is a N100/604).

Mikuni jets drawings

While you have the carby off make sure that you locate the mixture screw so you know where it is when you put the carb back on (its in a barstard of a place) as you will need to play with it as well.

The local shop pulled one out of an old carby as they didny have on and gave it to me for free but it should only cost $10 - $15.

 

[dumbassmini]

Hey guys. Been reading posts all weekend to try sort my carb problems out but still having headaches.
I've got a dhz 140 the crf 70 style with a mikuni 30mm carb on it. I started running it with 100 main and 20 pilot on the bottom needle clip and tried every part of the mix needle with no love returned. The valves have been done and the timing is spot on. Lots of spark but it still ran rough as with bogging down and stalling. I realize this is a no no but after trying other combinations of jets 22.5 and 25 pilot and up to 105 main I was still at a lose and and starting to get slightly demoralized. I then found it ran much better when I had the 22.5 and 100 in on second needle clip with screw out 2 turns if I had the choke half on. Which i assumed meant i needed bigger jets. But the plug chops I do always look sooty black which is to rich so I'm a bit lost. So I was wanting to know if anyone out there has got a properly tuned 140 with mikuni that could maybe share his/her jetting preferences just to give me a hand.
I would really prefer to fix it myself rather than take it to a shop. I just can't seem to get the correct t settings. I'm sure this is going to look like a simple fix to some of u but I'm lost lol
Thanks in advance for replies 

 

[sean01]

Hey guys. Been reading posts all weekend to try sort my carb problems out but still having headaches.
I've got a dhz 140 the crf 70 style with a mikuni 30mm carb on it. I started running it with 100 main and 20 pilot on the bottom needle clip and tried every part of the mix needle with no love returned. The valves have been done and the timing is spot on. Lots of spark but it still ran rough as with bogging down and stalling. I realize this is a no no but after trying other combinations of jets 22.5 and 25 pilot and up to 105 main I was still at a lose and and starting to get slightly demoralized. I then found it ran much better when I had the 22.5 and 100 in on second needle clip with screw out 2 turns if I had the choke half on. Which i assumed meant i needed bigger jets. But the plug chops I do always look sooty black which is to rich so I'm a bit lost. So I was wanting to know if anyone out there has got a properly tuned 140 with mikuni that could maybe share his/her jetting preferences just to give me a hand.
I would really prefer to fix it myself rather than take it to a shop. I just can't seem to get the correct t settings. I'm sure this is going to look like a simple fix to some of u but I'm lost lol
Thanks in advance for replies 

you need to find out where in the throttle action the carb/engine has it's most trouble..ie: idle-1/4, 1/4 to 3/4 or 3/4 to full

always leave the choke off while tuning, and clean the spark plug between every plug chop.. and i hope you are doing the plug chops properly..

also make sure you air cleaner isn't over oiled.. and make sure he choke isn't being pulled on with vacuum when accelerating..

the standard jets that come in the carb should of been spot on, only thing that would of needed attention would of been the mix screw and the needle height..

2 turns on the mix screw should be ok,
i would go 1 clip up from middle so it drops/leans the needle out

 

[dumbassmini]

Hey sean01 thanks for quick reply. Well I've chucked the 100 and 20 back in and second needle clip from the top and 1 and 3/4 turns out and even if I crack the trottle ever so slowly and slightly it just bogs and wants to die. I have tried less and more on the air/fuel mix but nothing really changes. I tried a plug chop but couldn't even let the clutch out to get going so not really possible. It has also started idling really strong and fast then it'll drop the idle revs all by itself and goes fast then slow if you know what I mean.
Cleaned the air filter and dried and lightly re oiled. Any ideas?

 

[sean01]

Hey sean01 thanks for quick reply. Well I've chucked the 100 and 20 back in and second needle clip from the top and 1 and 3/4 turns out and even if I crack the trottle ever so slowly and slightly it just bogs and wants to die. I have tried less and more on the air/fuel mix but nothing really changes. I tried a plug chop but couldn't even let the clutch out to get going so not really possible. It has also started idling really strong and fast then it'll drop the idle revs all by itself and goes fast then slow if you know what I mean.
Cleaned the air filter and dried and lightly re oiled. Any ideas?

sounds like a vacuum leak mate... check your manifold gasket and check that the plastic spacer isnt cracked or has a bad oring.. also make sure you tighten the carb to the manifold evenly..

another thing to try an locate the leak is spray water/wd40 or degreaser around the manifold joints.. if it idles up or wants to die then theres yr leak..

also is this a problem that just came about 1 day or can you pin point when it started and what you last did to the carb at that time.. reason i ask is usually these bikes run pretty close to perfect out of the box

 

[dumbassmini]

Ok cool I'll check it all tom after work and see what I can find. Hopefully an easy fix to the idle prob with the wd 40 trick and I'll take another crack at the carby. Hey if the bike is warmed up properly and you flick the choke on and the bike performs better what would that indicate to you? As for pin pointing when the idle started playing up... I did the valves and timing on Friday and since then it was screwy. I was playing with the carby a fair bit though so maybe I mucked something up. I'll go over everything and see what I can find.
Thanks again for the help man makes the problem solving a million times easier.