Loncin 150cc / KTM clone

[Mike38]

Has anyone bought one of these off of ebay? I'm having problems jetting mine. What's the secret? Mine seems to be running rich. I'm down to a 90 main jet, best it's run, but not good enough. A 87.5 main jet gets worse again. Could it be electrical?

[John22j]

Couldn't find any Loncin 150's on ebay -- do you have a link to what it's like?

What problems are you having with it --- have you confirmed it's running rich looking at your spark plug?

[Mike38]

Originally Posted by John22j

Couldn't find any Loncin 150's on ebay -- do you have a link to what it's like? What problems are you having with it --- have you confirmed it's running rich looking at your spark plug?

He doesn't have any of the 150cc bikes listed right now. A 250cc one just like my 150 is item number 190117707914. Mine acts real rich. The plug showed to be rich at first, but now looks almost perfect. Turning on half choke at above half throttle made it worse, so it's not lean, it's rich, or is it? The carb on my Loncin 150 looks to be the same size as the carb on my daughter's XR100. Maybe the carb is just too small to work? BTW, it's a no-name carb, but looks just like a Keihin. The Keihin main jets fit. As you can tell, I'm not too good at jetting carbs. Heck, it took me a month to jet a round slide Mikuni I installed on a Honda XL350.

[liverchip]

If the problem is present at idle and not at 1/2 to full throttle I don't believe your problem is the main jet, as most of these bikes use a slide/needle carb. Check the tech section for tips on adjusting the needle clip height, which will probably better the carb's performance.

[liverchip]

Of course the previous post is moot if it's not a slide. If it's a CK style Keihin clone(my 150 quad has one of these babies) Then jetting is the only option. Be warned that it has been known to happen where a bike may come with a bad carb from the start. Porous or leaky casting have been know to pop up here and there. In this case, finding another carb is the only solution. Since it's been relatively easy to find these carbs, replacing an untunable monster is a fairly cheap and easy solution.

[John22j]

My Hensim 150 will not hold and idle when cold - once it's warmed up it runs great though... I messed with it trying to get a good idle all the time, then figured it was just not going to happen -- it takes about 2 mins for me to roll the throttle a bit and fiddle with the choke to get the bike warmed up... then it runs great. Dunno if you might be going down the same path as well - if you are, might do like I did and give up on cold tuning and just focus on a hot bike.

Carb tuning can be frustrating sometimes, that's for sure (and I'm not an expert at it either)... first let's make sure of some basic things:

1. Air Filter -- good and clean (and if oil type make sure it doesn't have too much oil in it)
2. Take carb apart and clean every port (I'm guessing you've already done this) -- verify good flow and also that the float moves properly
3. Air screw is 1 1/2 turns out from fully in. -- we'll start from there (unless you have a setup manual with different stock specs)
4. New spark plug (NGK or anything that's better than the cheap ones most china bikes come with)

Once all that's been verified - can you give us more specific details on what the bike's doing... like rough idle, bogging down when you quickly go from 1/4 throttle to wide-full-open, popping from exhaust when letting off the throttle, popping from air box, etc.

[Mike38]

Originally Posted by liverchip

If the problem is present at idle and not at 1/2 to full throttle I don't believe your problem is the main jet, as most of these bikes use a slide/needle carb. Check the tech section for tips on adjusting the needle clip height, which will probably better the carb's performance.

....Nope, the problem doesn't start until I reach 3/4 throttle. The bike starts and idles great. Has good low end torque, just falls on it's face at 3/4 throttle. The carb is just like my daughter's 2001 XR100. Looks like about a 22mm Keihin. One thing I did forget to mention, it has a funky manifold. Almost a S curve shape to it. The intake port favors the right side just like a CRF150F, then the manifold turns sharply to the left, then straight to the rear. Could be that it's just not getting enough fuel to run at more then 3/4 throttle. Maybe I'll pull the manifold off and clean up the inside with a Dremel for better gas flow. I took it for a ride tonight with my son on his Rocketta 125. I can smoke him off the line, but once mine starts that blubbering, he can stay with me. Anyone have any help? Thanks.

[liverchip]

Ahh ok that changes things a bit. I have had this problem with 2 different bikes and 2 different causes. The first was my GY6 quad. At over 1/2 throttle, it would sputter and kick. I found a loose ground at the ignition coil. The second was my bike. Similar issue. This was caused by plastic shavings in the fuel tank blocking the intake screen at the petcock.

[Mike38]

Originally Posted by liverchip

... I found a loose ground at the ignition coil. ...

.
Liverchip, you're my hero! That's exactly what was wrong with my 150. I looked up under the tank, found the coil, and it was very loose. What happened was the bolts were tight, it's just that the threads in the frame were not tapped deep enough. I stuck a flat washer on the bolt, and tightened it up. Put in the original main jet, and let me tell you, for a $305 dirt bike, that thing rips! Thank you very much.

[liverchip]

Glad to be of help