Basic chinese bike troubleshooting guide

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Hi everyone!

Since I wrote a couple of guides relating to our experiences with a 110 chinese quad and a 250 dirt bike, I've had a few queries from people who have had some difficulties with their bikes. I'm not an expert in any way, nor a trained mechanic, but I've had some experience with keeping our bikes running and troubleshooting issues as they've happened. I thought that I'd put them down into a guide that may help other people. As I find more information and resolve issues with our bikes, I'll add the details to this guide.

At the moment we have a 110cc Quad, a 125cc Quad, a 125cc Pitbike and a 250cc dirt/trail bike in the family. A friend has a 110cc Buggy. Bike brands vary, but there are zongshen and loncin motors in them.

Anyway, here are some queries I've received that may be of help.


Here we have a Quad that is proving hard to start and keep running

Hi I was hoping your still doing your guides to 110cc quads if so I've just bought a
second hand one put a new battery in it. It starts only with full choke and if I turn
the choke off it runs for about 15 seconds then stalls. I have had it going around the
yard but it stalls every time after a short while. Im suspecting its the carby, any help
would be great thanks.


Here is my response:

Hi Mate,

Sounds like a carby problem for sure.
Running on full choke and then dying when you turn the choke off sounds like there's just not enough fuel getting through.

You can take the carby apart and give it a good clean, make sure nothing's blocked and fuel can get through. You can have a play with the mixture screw on the side of the carby as well. You never know, the previous owner may have fiddled and set it wrong. Note that there will be two screws, one for idle speed setting, the other for mixture.

If you don't have any luck with that, a spare carby will only cost you around $15-$25 from the bikes spares category here on ebay. Do a search for 110cc and have a look to see that yours looks similar to the one on the listing.

Best of luck mate and let me know how you get on..

Here is another Quad that is proving hard to start

 Dear Farnk666,
Noticed your guides and am wondering if you could help me with my 110cc
quad which is approx 3 years old and won't start at all.
I have replaced coil, spark plug, & cdi unit, it kicked over once but
now only makes a clicking sound. Should I replace the starter solenoid
or could it be something else????

Would appreciate any advice.

Ebay Member

Here is my Response:

Have you tried a set of jumper leads? Will it turn over with the starter
motor then? If the jumper leads work, get it running and check the voltage
across the battery. You want to see about 13 Volts DC. If not, then the
regulator might be faulty and not charging the battery.

The battery itself could also be cactus. I've had the one in our Quad die.
It showed a good voltage when disconnected, but dropped to nothing under load.

A single clicking noise when you try to start it would indicate that the
starter solenoid is doing it's job. If it's a regular clicking noise,
then there will probably be a problem with either the starter motor or
maybe the starter clutch.

As a check for the starter motor, short the starter motor wire directly
to the positive battery terminal, does it turn over? is there a clicking noise?

From what you're telling me it sounds like there's not enough juice in
the battery to turn it over. Try jumper leads from a car battery and Check
the wiring from battery to starter solenoid and to the starter motor.

Once you get it turning over with the starter motor, check for spark with a spare plug shorted to the engine cases.

If it's been sitting unused for a while, it would be worth while to drain the
carby and fuel tank and fill up with fresh fuel.

Let me know how you go!



And another Quad that is hard to start!


Dear farnk666,

Hi I recently bought one of the chinese 110 cc quad bikes from (deleted) and have
been having problems with it. I havent been able to get an email thru to them so far and
was wondering if you might have some ideas on the workings of these little engines.

Mine gets used in the paddocks for herding sheep. It got a bit warm the other day and now wont run properly and takes about 20 mins of cranking the crap out of it to start. Would
you be able to give me a few ideas on what I can do as I haven't even finished running it
in yet. Its only a week old and as you said in your guide aftersale service is non existent
any way cheers hope to hear from you

Ebay Member


Here was my response..

Hi There,
Sorry to hear that your quad is giving you some troubles.
I'd suggest to go back to basics and do some troubleshooting. So, I don't know what sort of mechanical experience you have, so excuse me if I get a bit basic, or if you have already tried these things. I'm not a trained mechanic, but have had a bit of time keeping our two bikes going.

Your mail said that it takes ages to get it started, does it go OK once it starts?
I'll assume that is it OK once started and that it's starting that is the problem.

If the engine does actually run once started, then it's a good indication that
there's not much wrong mechanically inside. Loud banging / grinding or tapping noises
would indicate a drastic mechanical problem.

So, usually poor starting is either due to weak or no spark, or a lack of fuel.
When you crank the bike over, is there a smell of petrol from the exhaust? If so, then
your engine is probably getting fuel OK. Once it starts, does it rev cleanly or roughly? Rough or stuttering response to the throttle could indicate a carbie problem.

Next take out the spark plug. Have a look at the end of it. It should be a darkish grey in
colour, but not covered in sooty deposits. If it's dirty, replace it or you can try to gently clean it up with a wire brush. Have a look in the bike's manual and find the plug gap that is specified. Use a feeler gauge and either open up or close the gap accordingly. 

With it out, plug it back into the plug lead and touch the outer body of the plug against the engine. Now, crank the engine over as normal. It won't start with the plug out, but you can look at the spark plug gap to see if you are getting any spark there as the engine turns over.  Be careful when you do this and make sure that you are not holding onto the metal part of the plug or you will get a spark yourself!

If you don't see a spark then try the following, each time looking for a regular spark as the engine turns over. When you get a spark, refit the plug and try starting the bike: 

  1. Try another sparkplug.
  2. If your quad has one of those kids safety cut-out switches that kill the ignition circuit then remove it. (my young bloke's had one on the rear, which caused a similar problem one day. I just had to unplug the connector on mine, check the wiring on yours to see if you need to short out the pins inside to keep the ignition circuit going.)

  3. Follow the wiring back to the coil, then the little black box (called a CDI unit)
    and make sure that all the connections are OK.
    (I pull apart the electrical connectors and spray them with a squirt of CRC every now and again)

  4. Try a new CDI unit

Hope you have luck!



A couple of days later I got a message back, it appears that the spark plug was the culprit!


Dear farnk666,

Gday, I finally sorted it today. It turns out the gap on the spark plug was a bit over, so made the spark weaker. Got a new ngk plug and used that instead with a .7 mm gap. Went and replaced a lot of the wiring and connections just to be sure and recalibrated the carby from scratch. It was a bit difficult to get started again but after a while i got the sh**s with it, took out the spark plug and sprayed some of my lynx deoderant in the chamber and it started first go ! (didnt have any start ya bastard or anything lol )

Once I had it running I finished setting up the fuel flow and now don't even need to use the choke to get her going. She now has more power and I frequently find myself drifting unexpectedly on sharp corners. So anything else useful to put in a guide, go for it. The more info out there to help folks with probs the better. I spent hours looking on the net trying to find info on the loncin motor and it was almost impossible. It just goes to show that all it takes is something small to mess it all up anyways. Cheers for the advice mate!

(Ebay Member)



Here is another one regarding vibration

Dear farnk666,

hello, I see your short reviews on the generic chinese built 110c 4 wheeler.
Do you know how to reduce the vibration on these? It would be nice to cruise around the
neighborhood with my daughter but it vibrates so much at ~10 mph. Thanks, <deleted>


Not a lot to suggest I'm afraid, These 110cc singles are quite buzzy beasts..

Dear <deleted>,

Hi there,
No real magic solution to this, as the vibration is generated by the engine as it is running.
As far as I know, these motors don't have an internal balance shaft as a lot of Japanese and European (I think) singles did.

Anyway, you can try a smaller rear sprocket, which will lower the revs for any given vehicle speed. The revs at your cruising speed will be lower, and you will have less vibration. Of course if you go faster, the vibration will also increase. This will also effectively reduce engine power, but give you more top speed.

You could have a look at the frame and see if there is room to modify the engine mounts to accept a rubber spacer or block. This would be a bit of work however. Perhaps you could find a local engineering firm to have a look and advise you.

The exhaust pipes tend to be solidly mounted as well, put a rubber washer or spacer on the exhause pipe mount. Not sure what difference it would make, but I've seen foam handgrips at bike accessory shops, perhaps they might help?

On my old roadbike,(82 Ducati) I put a sheepskin on the seat which helped with annoying vibration, not sure that would really work on a quad tho.

- farnk666



Now we have a 250cc quad that is hard to start..

Dear farnk666,

Hi, bought a new 250cc chinese quad bike and I'm having a problem with it.
As I'm not very good with motors, I've replaced the starter motor and replaced
the battery and relay, but after many hours and headaches it will not start.
I can clutch start it ok and i can also start it with jumper leads. I've replaced
the spark plug as the old one was very very black!!!

When I try to start it turns over but does not start.

CHEERS <Deleted>


My response.


Hi Mate,

When you start it with the jumper leads, does it start easily? or does it take a
while to get going?

The fact you can clutch start it indicates that there is nothing that drastically
wrong with the motor or carby itself. Can you kick start it?

If you are easily able to jumper start the thing, that would indicate that there
is not a lot of power getting to the starter motor when you try to start it from
the bike's battery normally. It may be turning the motor over too slowly.

Replacing battery, relay and starter motor are the correct steps. Without seeing the
bike, perhaps you have a poor connection or dodgy bit of wire somewhere that is not
letting enough current through to the starter motor from the battery.

Next step I reckon is to replace all the wire and connectors from the positive battery
terminal to the relay and then to the starter motor. Get some heavy gauge wire and
good quality crimp conectors from an auto electrician.

I'd also check that the battery negative terminal and the starter motor are well earthed
to the motor and the frame. That will make sure that the current can get through the

When you get it going, a good check is to put a voltmeter across the bike's battery and
start the bike. Rev the bike and look for the change in voltage as the revs rise off idle.
You want to see about 13 volts. If it's lower than 12 or so, then your regulator could be
cactus and not charging the battery.

Best of luck and let me know how you go!



Now it's a 'Clicking'or tapping noise from a 125 while it's running.


Dear farnk666,

I bought a 125cc pit sports/motor bike for my son. I had to govern it down a bit, it was too fast for him. I'll get it back to normal when he's used to it . The bike is running well, but all of a sudden there was a slight ticking only when moving, not when idling. When I got down and had a listen it sounds
like it's coming from the chain, could it be the chain running over the guides? Should I be concerned? thanks



My Response

G'day mate,
Good idea to govern it down. I've done the same thing myself!

With the ticking noise, does it change rate with the bike's speed? From what you have described it sounds like the chain could be too loose and is running and rattling over the guide. A loose chain is a problem, as it could jump the front or rear sprocket and cause some damage. 

I didn't have much experience with quad/dirt/trail bikes before buying ours and it took a while to get used to the right chain tension.

Check out the whole chain run, look for anything that is fouling the chain, and also look for chain marks on the frame and guides. Finally, I'd check the chain itself, look at each link and make sure that there isn't a link pin working loose.

Other than that I'd get a bike mechanic to have a look. All the best!



Now a 250 that doesn't want to run.


Dear farnk666,

Hi Farnk, I just bought a (XXX) 250cc a couple of days ago. I assembled it and took care. I couldn't kick start it, but I charged the battery and had no trouble. I used it for maybe 15 minutes and it conked out. I thought I stalled it because I was in a high gear, but now I think otherwise.

I couldn't get it started again for the life of me. Seems to really smell of fuel so I thought I flooded it. Since then it has the same problem. I can start it after leaving it for ages but then it only runs for a few seconds. The spark seems really low/not existent. This arvo I made sure the battery was fully charged and tried it again. It started straight away with the choke but then conked out a few seconds later. Any ideas?


My Response

G'day Mate,

I'd start out changing the spark plug. The poor / weak spark could be just a dodgy plug. You can do a quick check with another plug. Plug it into the lead and earth it on the engine case. Have a look at the spark while the bike turns over. If that looks better, gap a new one and whack it in. If there is no change, work your way from the plug lead cap, to the coil and back to the cdi unit, checking connections all the way.

The battery may not be holding enough charge even though it shows good voltage. Another test is to connect up some jumper leads to a car battery and see if the bike behaves the same way. My son's quad battery showed great voltage with no load, but it dropped to almost nothing when under load.

That you can get the bike to fire up at all is encouraging so I'd assume that the coil and CDI unit will be fine. A smell of fuel indicates that the carby should be ok. At least some fuel is getting in!

I leave my bike with no choke at all, once it's up to temperature it's not needed and when cold, the thing dies all the time. I can't kickstart the thing when it's cold at all. When it's warm it kicks over fine.

Give it a go and let me know how you get on!



Another issue of an electrical nature!

G'day mate....

I stumbled across your tip guide for quad bikes, the almighty chinese ones!

I have just got one given to my kids from my parents. Second hand. The battery has just died, 12v under
no load but stuff all volts when any sort of load is connected. But a question i do have is, with
the head light on and the engine running, what sort of voltage would you expect across the

I am getting 12.5 -12.7. I am of the thoughts that that is a bit low. Any thoughts? I
would still be under the impression that I would get around 13V still.

Is there a way to check the regulator or even do a resistance check across
the stator. And what ohms would i expect. I appreciate the time you have spent helping us
newbies out.


My Response

That sort of voltage would be what I'd expect when the battery is stuffed. Really, anything over 12.5v would seem to indicate that your reg and alternator is ok.

I'm not sure of the resistance you should see on the windings, I've never had to troubleshoot that far. I'll have a look at ours and update the guide at some stage.

Best check for the reg would be to swap it with one from another bike, then measure the voltages on each bike to see if anything changes.  

I had exactly the same thing happen with our 110cc quad. A new quality (Yuasa) battery fixed it. I get just under 13v with the motor running and the headlight on.

If you had a stuffed reg or stator coil, you probably wouldn't be getting even 12v!

Swap the battery over and let me know how you get on.




Since I wrote the two guides a while ago a couple of other issues have cropped up with our bikes.

  • I went riding recently and the 250 just didn't feel 'right', there was a lot of sloppiness in the front end. I put the bike up on the stand and found that the two front axle carriers were loose. These are the parts located at the bottom of the front fork tubes, and carry the front axle, brake and wheel. They bolt up to the bottom of the fork leg. The bolts are covered by the ruibber seal. I popped off the seal, cleaned the bolts and nipped them up tight with some loctite. Problem sorted!


  • The 250 started leaking fuel. This was due to the type of fuel line fitted to the bike at manufacture. I'd suggest checking your fuel line at the very least to see if there is any evidence of cracking or perishing of the line. Automotive spares shops sell fuel line by the meter for a few dollars. Be sure to take a sample of the line with you as it is very important to match the internal diameter of the tubing to ensure a tight fit on the bike. Make sure that you also fit hose clamps to the fuel lines.


  • After riding the 250 in wet weather and mud, I found that the rear suspension linkages and pivots have no seals to protect them from water. (This is one of the detail type of things that separate a $1000 chinese bike from a $7000 or $8000 Japanese one!) Just a day after riding I found the start of corrosion in the swingarm and linkage bearings. It's critical to keep water out of these areas, so be very careful when using a pressure washer and have a good look over these areas when you've been riding in the wet. 


  • After the young Bloke had spent a couple of weeks at his Grandparents farm, the 110cc Quad needed a fair bit of attention. The chain had stretched past the limit of the adjustment available, the swingarm pivot bolt retaining nut had gone to god, and there was a lot of slop in the front end steering joints and rear axle. We put aside a whole Saturday to take the Quad to bits, hit it with degreaser everywhere and clean and reassemble everything, using new nuts and bolts, washers and good quality grease in all the linkages and bushes. This was a great day and an opportunity to teach my young bloke some basic mechanical skills. While I was working on more detailed bits, he was on cleaning duty. After a day's work the quad is going really well and looking great. The chain was the original one with the bike and has lasted for 18 months. Not bad. I would count on spending a day like this every year. 


  • The exhaust on the 110cc Quad and a mate's 110cc Buggy both cracked in the same place. These 110cc engines produce a lot of vibration at higher revs, and the mufflers are solidly bolted to the frame. This means that the exhaust pipe is constantly being flexed by the engine against the frame. In both cases, this caused cracking and separation of the muffler from the exhaust pipe. The metal is VERY thin in these exhaust systems and not easy for a beginner to weld. I know! Once repaired or replaced, place a rubber washer between the frame and the muffler's mounting bracket. In both cases this has stopped the exhaust from cracking. A 20c rubber washer will save you $40-$60 odd for a new exhaust!


  • On a similar note, the 110cc buggy has cracked part of the rear subframe. This subframe carries the engine and rear axle and is mounted to the frame of the buggy via a pivot and the rear suspension. It appears that vibration from the engine along with the shocks from some enthusiastic off-road driving by the kids has been too much for it. If you have one of these buggies, keep an eye on the rear and look out for any signs of cracking in the frame tubes. The fix is to remove the engine and subframe and get it welded!


  • The Buggy has a bit of an appetite for clutches. We're 12 months in now and it's had 3. Not a big problem as such, but something to keep in mind if you are looking for one of these. Get yourself a couple of spare clutches and the tools required to change them over.


  • The 110cc quad has been a bit hard to start when it's been sitting in the shed unused for a few weeks. Draining the carby, cleaning / swapping out the plug and charging up the battery seem to get it back in running order. 


  • Our 125cc quad has a single hydraulic disc brake and the sprocket carrier on the rear axle. After a few hours use, there was a problem with the rear brake. The brake disc carrier is secured to the axle by a couple of large nuts which had come loose. I treated the brake disc and drive sprocket carrier retaining nuts with some loctite and nipped them tight. Problem sorted!


  • After the first 30-45 minutes of running in the 125cc quad, we had some difficulty changing from forward to reverse gears and back again with the bike running. You could change gears easily if you stopped the engine. The problem was due to the idle speed being too high! The idle speed had risen as the engine loosened up after the first few minutes. Once the engine revs past idle, the centripetal clutch was engaging the gears which made changing to reverse / forward difficult. The fix was to adjust the idle speed back down.


  • We had a fuel leak from the carby overflow tube on the 125cc quad. This was a 30 minute job to fix by removing the carby from the bike, removing the bowl and cleaning the inlet valve. I also adjusted the float level. (Update) we had more fuel leak issues with this bike, so instead of further mucking about, I replaced the whole carby with a new one ($19).


  • The new 125 Pitbike seems to be going quite well, although it's early days. As with the 250cc bike, we replaced the brake caliper and suspension mounting bolts with Unbrako ones and liberally applied Loctite to everything, working methodically from the front wheel to the back. Maintenance on this one looks to be a much easier deal, as there is no battery and the thing is very basic in it's layout.


  • I'm sad to report that the 110cc quad may have had it's day. On a visit to Grandma's farm, I was told that the quad was " A bit rattly " and "Something might be wrong". It turns out that the exhaust had been ripped out of the head, (taking a stud with it), and the starter motor (mounted on the bottom of this engine) had been knocked so hard that the crankcase was cracked at the starter motor mountings. When I pulled the quad apart, I also found that the frame had cracked as well! I didn't see it happen but someone must have hit a rock VERY HARD! The young bloke has outgrown this bike so it's not a major drama and I'm happy that we got 3 or so years of pretty hard use out of it. I'll keep an eye out for a whole 110, 70 or 90 cc motor and we might get it going again for his younger sister after a bit of welding.


  • I've recently had a bit of bother with the Young bloke's 125 pitbike. The problem was that the chain kept loosening and the rear wheel was always out of alignment. Having a bit of a look at the bike, I saw that the spacers between the back wheel bearing and the swingarm were small in diameter, and there was not much metal area in contact between the spacer and the swingarm. This meant that the clamping force holding the wheel in position was being applied in a very small area. I had a mate turn some new spacers on his lathe and the wheel is now secured!


  • It also occurred to me the other day that is it a bad thing to dump the clutch in 1st gear with a fist full of revs and not let go when the bike decides it's had enough of you. Bruised my pride, but the bike was fine after a pretty heavy dumping. The X-motos 250 is a little rough around the edges but it's tough where it counts..



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