lifan 140cc which carb to use?

[blue_vl_t]

i have searched this subject quite a lot, i just cant find out a few things.

i'm changing my motor from a jialing 125 to a lifan 140, as my engine has some damage, and on my 125 motor i seem to have a mikuni 22mm oval bore carb(advertise as a 25 or 26mm carb)

I was thinking of trying the 22mm carb on the stock 140 and see how it goes, do you guys know if this will go very well, i'd like it to perform as well as it can. I realise it will/may need re jetting etc.

The other thing i was looking at was the 26mm flat slide carbs that DHZ have on ebay, they seem so say 24m on the side of them though, perhaps the 26mm is actually the same carb as the 24mm?? Anyone able to confirm this?
perhaps the 24mm one will be best suited anyway?

the other option is obviosly to buy a 26mm mikuni carb(advertised as a 30mm)
the motor comes out with this standard and perhaps will the be the best suited.

Any suggestions welcome, cheers guys

 

[Cactus Jack]

First of all just give your 22 Mikuni (aka 25/26) a go to see if you like it ....... the jetting shouldn't be too far out since a 140 is only 15 cc bigger in capacity , it'll just lose a bit off the top end ...... give it a throttle chop plug read to make sure it's not running too lean ......

Over in the US they're now saying that 26 mm OKO's are the best and easiest to tune carbs ..... whereas before it was the Genuine VM26 Mikunis ......

The only thing I've noticed is the OKO they're talking about appears to be a round slide carb ........ and very similar looking to a VM26 Mikuni .... at LEAST they've now found that a #105 main jet is a good starting point for tuning carbs for small bore 4 strokes .... something we Aussies have known for donkeys years ....... Ozzy , Ozzy , Ozzy , Oi , Oi , Oi ........

26mm Performance Carb Kit - Oko 26 - Race Head

The carbs DHZ are selling will be 26 OKO's - they're probably just showing a 24 to save redoing the pics ...... email Ken first to verify that he'll be sending you a 26 and if you still get sent a 24 .... send it back ......a 26 mm carb should work the best overall since the BVH inlet ports and intake manifolds are 26 mm . Mack said he got a 28 OKO working great on a stock 140 but he used a fatter exhaust pipe .

Half the fun of owning pit bikes is the experimenting you can do with them cheaply ... then simply flog off the parts you don't end up using ........

 

[blue_vl_t]

thanks for that, helps a lot.
i assume you mean take the bike for a quick spin once warm and check the plug colour for if its running lean?

yea the carb i was thinking was the 26mm oko dslide/ flat slide or whatever it is, so it should have 26m written on the carb, cool, cheers for the info.

anyone elses opinions welcome.
cheers simon

 

[MITTZ]

cactus jack is like the most usefull guy on here!!! he knows everything about everything! you know if youv got any tech question therel be a nice long detailed explanation from him! its great!!!

 

[cass38a]

You are nearly right with the plug chop. The most important thing is not to just check your plug after you stop but it is how you stop that makes the reading correct.

What you need to do is find a good straight bit of track (prefereaby up hill) and ride your bike on full throttle with the engine under load for about 10 seconds. Then without releasing the throttle you need to hit the kill swich and pull in the clutch at the same time. Then get you get your plug spanner out and check your plug. Your bike shoud be at normal temprature when you do this so ride for 10 minutes beforehand.

Doing it this way tells you if you have the right size main jet. If you just coast to a stop your plug reading may tell you that your bike is running rich when it is way lean at full throttle.

 

[ducar.r.spec]

sorry to go off topic
but dude would u be interested in selling parts out of the jialing bottom end???
im missing a few bits
please get back to me
cheers
reece

 

[Cactus Jack]

Here's a good thread on tuning carbs ...... it's pretty informative .........

carb tuning help - Planet Minis Forum

Thanks for explaining throttle chops Cass ........ all I'll add is that when reading plugs , clean your plug first , then do the test .... black is too rich , white or grey is too lean , and medium to light tan is just right .

 

[blue_vl_t]

Not sure that i want to part with the jialing yet, sorry.

i took the bike for a ride today to run in the motor, i have the 22mm carb still fitted, i found the spark plug colour to be white/ light grey for all throttle positions, i remover thr top of the carb and fount the needle to be on the second highest setting. I then moved the needle to the highest setting, but this was obviosly not enough. So the plug is still white. I pulled the carb down to find a 95 main jet and 15 pilot jet.

I will try and get hold of a 105 main jet and see how that goes i think.

Overall, besides the white spark plug the bike is very responsive, it has a irk kit in too.
I was able to jump on and off my bike and onto my mates bike with the same motor which was interesting. His has the 26mm(true size) carb and no IRK fitted.

the two bikes seem very similar in peformance top end, but the responsiveness on mine seems a lot better.

 

[cass38a]

I would probably get the OKO or a bigger Mikuni (26mm) instead of stuffing around too much with that carbi you got. As cactus said your top speed is probably restricted with your current carb (unless your happy with the top speed). But you dont want to do too many K's with it running lean as its not real good for them.

 

[tubes380]

i took the bike for a ride today to run in the motor, i have the 22mm carb still fitted, i found the spark plug colour to be white/ light grey for all throttle positions, i remover thr top of the carb and fount the needle to be on the second highest setting. I then moved the needle to the highest setting, but this was obviosly not enough. So the plug is still white. I pulled the carb down to find a 95 main jet and 15 pilot jet.

you should be moving the needle clip down, to richen the mix up, when you moved the clip up you leaned it out even more

 

[motoXXX]

yes moving the e pic down makes it more richer, not leaner up is leaner so u just made it worse

 

[blue_vl_t]

you should be moving the needle clip down, to richen the mix up, when you moved the clip up you leaned it out even more

Oh, i wrotre that incorrectly, the clip was on the second from the bottom and i moved it to the bottom. What i'm saying is the needle is/was at the highest point possible. sorry bout that.

I fitted the 105 main jet today, and moved the needle to the middle position, the bike feels about the same to ride, although i cleaned the plug and am not able to get any colour on the spark plug(after a short ride once warm) The plug is just clean, these modern fuels are shite for plug colour, anyone know if there is a fix to get my light tan colour???

I also now have a hesitation at light throttle(below 1/4) and when coasting a bit downhill without the throttle has a crackling noise from the exhaust. i wouldnt have thought the bottom end tuning would change with just the main jet. sounds lean??

 

[cass38a]

Time to have a play with your pilot circut / mixture screw.

 

[Cactus Jack]

When they say "#105" main jet ........ they mean KEIHIN #105 jet size ........ Mikuni runs a different method of grading their jets and that's where some confusion can enter the picture ........ a Keihin #105 main = a Mikuni #95.6 main ...... with these knock off Mikunis , you have to check the actual drill size to know exactly what the hell they are (Mikuni doesn't appear to make a "#95" ) and #105 Keihin = 0.040 (40 thou) . Since you are STILL using your 125 Jialing with the stock 22 mm Mikuni .... there was no real need to change your main jet IF it is a Genuine Mikuni sized jet ....... except to a #95.6 Mikuni jet or slightly bigger if you have fitted a pipe and it's running leaner .

Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3

You're right ! It's hard to get a good plug or pipe reading with unleaded fuel - especially if it has Ethanol in it ...... I'd look at the colour of the carbon on the piston .... if it's black , then the engine ain't too lean by any means ........

 

[blue_vl_t]

thanks for the info there mate, exept you may have misread, because i have changed from a jialing 125, and now am running a 140 lifan.

I didn't actually measure the jets, but i think the 105 looked bigger than the 95 i bought, perhaps jet drills would be easier, at least i'd know what was happening.

Anyway i rode the bike again tonight for an hour or a so, i lifted the carby needle to the highest spot to try ands get some black on the plug so i knew it was rich, but the bike just ran spot on, and the light throttle hesitation and stalling dissapeared. seems to be running sweet. The plug is stil clean as a whistle though.

I thought i may put an air/fuel ratio on and oxy sensor in the exhaust and put the autronic on my handlebars, at least i'd know whats going on then hey.

I appreciate all the help boys, sorry i normally stuff about with rb30's and turbo motors, so all this is a little different.
cheers simon

 

[Cactus Jack]

Not sure that i want to part with the jialing yet, sorry.

LOL ...... Yeah I went off the above comment ........ Your #95 MUST be a Keihin sized jet then since a #105 Mikuni jet is equal to about a #117.5 Keihin jet and your engine would run sluggish with a jet that big in it ........

Width------Keihin # -- DynoJet # -- Mikuni #
0.0450---- 117.5------- 112--------- 105.0

It's great to hear that the #105 worked out .......

 

[numroe]

Cactus, Your post (below) is very useful thanks. Related question:

I have two carbs to choose between for my Lifan 140: Mikuni (copy) 24mm and an OKO26. What I'd love to understand is why at WOT my engine feels similar (maybe a little stronger with the OKO) when the main jet in the Mikuni24 is a 97.5 (41 thou) yet the main in the OKO is a #100 (38 thou)? In other words, why and/or how does the OKO pull so much fuel through the 38 thou main jet to run correctly?? eg. bowl and/or venturi design?

btw: I've tried a 95 and 100 in the mikuni and 97.5 (stock) or 95 was best (28C and humid at sea level). Pretty easy to feel the diff. I've also tried 102.5 (stock) and 105 in the OKO26, and without doubt leaner is better. It struggles to rev on a #102.5 and is much worse with the #105.

Lastly: To be sure my OKO26 is running as good as possible I want to try going one leaner on the main. But I could not buy a #97.5 Keihin main jet anywhere! Why are < #100 mains so hard to find?? Luckily I did get someone to drill two #75 mains out to 0.90 (35.4 thou) and 0.95mm (37.4 thou). So I hope I now (according to your lovely table) have roughly a #95 and #97.5.

When they say "#105" main jet ........ they mean KEIHIN #105 jet size ........ Mikuni runs a different method of grading their jets and that's where some confusion can enter the picture ........ a Keihin #105 main = a Mikuni #95.6 main ...... with these knock off Mikunis , you have to check the actual drill size to know exactly what the hell they are (Mikuni doesn't appear to make a "#95" ) and #105 Keihin = 0.040 (40 thou) . Since you are STILL using your 125 Jialing with the stock 22 mm Mikuni .... there was no real need to change your main jet IF it is a Genuine Mikuni sized jet ....... except to a #95.6 Mikuni jet or slightly bigger if you have fitted a pipe and it's running leaner .

Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3

You're right ! It's hard to get a good plug or pipe reading with unleaded fuel - especially if it has Ethanol in it ...... I'd look at the colour of the carbon on the piston .... if it's black , then the engine ain't too lean by any means ........