yx 140, lifan & yx125 problems

[funfisher]

Hi all,
I need help, (most people that know me have been telling me that for years, especially my ex wife lol)
ok, we have three bikes, ( hence the title of this) one has yx 140 in it, one has lifan125 and the other has yx 125, so to make it easier to understand I will call the 125's one motor because they have the same issues, thanks to the help of you guys on here I have sorted a lot of the probs with these bikes but a couple niggly things, before I start I have done the valve clearances on all three bikes and all are stock standard

YX 140
all standard, molkt carby, I assume 26mm, the throat where it joins the manifold messures 26mm, but has a big slide compared to the 2 mikunis on the 125's, the slide is 30mm the mikunis are around 24-25mm slide.
this one goes ok, nice and snappy on the throttle, does crackle a bit when you get off the throttle quick and does lag slightly,( not much tho) the only drama I have with this one is it just wont idle nice, it will only idle ( hot or cold) if I turn the idle screw up but even then it very very lumpy, idles high then drops, I only get a nice idle when the mixture screw is turned all the way in tight, but then the bike seems doughy when riding, I assume this means a change of pilot jet, but there lies the prob, I pulled the carby apart and the pilot that is in it has no markings on it at all, I thought the molkt carby took mikuni pilot jets and oko mains, but this pilot jet looks completely different to them, it only about 8mm long and the last half is fully threaded, the jets in the mikuni are twice as long either side of the threaded bit.....

yx/lifan 125 mikuni 26mm
these motors both have the same problem so I assuming its jetting again,
they just have nothing down low, idle ok, but in neutral, the throttle seems unresponsive, they seem as though everything you do with the throttle happens slowly, even 2-3 seconds later, from 1/4 to half throttle upwards all good, same when riding them, in 1st and second gear nothing, third gear and more revs go great,
pilot jet in both size 15 main 95. looking at the needle, both have 5 positions and both on the second slot from bottom of the needle

sorry to post a bloody essay but trying to give as much info as possible

Thanks heaps

 

[my67xr]

have you checked them all for vacuum leaks?
start and let them idle,
spray wd40/carby cleaner/degreaser etc on the carby-insulator join,then the insulator to manifold, and manifold to head joins.
even spray the fuel bowl to carby base join too
if the idle changes in any way then there is your leak.

with the 2 Mikuni copy carbys,
try a #20 Pilot jet in them both, that should help them a little.
how many turns out are the mixture screws?
try them about 1.5-1.75 turns out, (from being done up fully)

 

[8r3nd0]

have you checked them all for vacuum leaks?
start and let them idle,
spray wd40/carby cleaner/degreaser etc on the carby-insulator join,then the insulator to manifold, and manifold to head joins.
even spray the fuel bowl to carby base join too
if the idle changes in any way then there is your leak.

with the 2 Mikuni copy carbys,
try a #20 Pilot jet in them both, that should help them a little.
how many turns out are the mixture screws?
try them about 1.5-1.75 turns out, (from being done up fully)

+1 exactly what I was gonna say but Craig said it. 140 has a vacuum leak somewhere.
125s need mixture set correctly or bigger pilot.


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