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Mixture problem?


Sand bags
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Hi all,


Recently bought a cheap zontes tiger 125, my first bike. I understand a lot of people aren't keen on Chinese bikes, but I just wanted something cheap geared bike to practice on for a few months before I do my license. Also using this opportunity to get familiar with working on them. Onto the problem...


When I got the bike, it was starting up, then once it was warm to was idling high at 4k revs. So I adjusted the idle screw down, and I can get it down to just above 2k (if it's warmed up properly), if I go lower and hit the throttle it bogs down or cuts out. Which is probably why they cranked it up.


I took the carb off today, gave a good clean, had no effect. I'm wondering if the air/fuel mixture is correct. Does anyone know what it should be set at?


Would also appreciate any other advice on what the cause might be. I cant see any obvious vacuum leaks. But I read a way to test it is to spray start fluid in different areas to see if it gets sucked in from anywhere and increase the idle, so I'll give that's try to be sure.


Thanks in advance

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I don't know but experience tells me its probably about one and a half turns out plus or minus a quarter turn . Screw it in gently and carefully count the turns . If it's something silly like four to six turns then you will know you're on the right track . If it's anything between one to three turns then start at one turn and bring it out a quarter turn at a time until you get the best performance and write notes as you go . If there's no improvement then at least you will be able to go back to where you started and look at other reasons for poor running. Not wishing to confuse matters, I personally don't get why people refer to Pilot Air Screws as Mixture Screws . A Pilot Air Screw only really controls slow running, after that It's factors such as float height, jet size and needle position that govern performance. If none of this tweaking works then I would turn my attention to the float height or more importantly , the fuel level . By the way, someone hasn't stuck a pod filter on this bike by any chance ?

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As Bob says, a turn and a half is a good starting point in the absence of knowing any better.

You checked all the basics first, spark plug,air filter,throttle slide moves freely.

Is it a CV carb?

How did you check the pilot circuit was clean?

It should have a jet from the float chamber and an air bleed from the filter side of the throttle slide.

At idle the slide is pretty much closed and the air is drawn through the pilot bleed,mixes with fuel from the chamber and into the engine.

Use something like carb cleaner to squirt through the pilot circuit to check its free flowing.

Don't poke about with bits of wire or anything you can easily damage the jets.

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Hi all, thanks for your responses and sorry for the delay in replying.


Right, what u have done in total is...


Took carb apart. Cleaned out all jets and any holes - wasn't really dirty at all tbh but gave it a clean anyway. Didn't make a difference.


I played around with the mixture screw/pilot air screw. Started from 1 turn and went up slowly, wasn't helping. It is a right pain to adjust this screw when it's on the bike, as you can't get a screwdriver in there annoyingly, had to use pliers and a Stanley blade in the slot lol


After that I took the carb off again and adjusted the float. I had a read up, and found that mine was not sitting parallel as it should, and was quite a bit off. I adjusted that, out it back on, and saw some improvements. I now am able to start the bike up easier. Start up with the choke on, and can turn to half choke immediately and it will idle comfortable just under 2k (which I believe is still a bit high?)


It's drivable now but it still has the problem of bogging/almost cutting out when I give the throttle a quick acceleration. Not so much when I drive it, because I haven't been flooring in first gear. But when I have it in neutral, give the throttle a quick twist is bogs. If I turn it not so quickly it revs up no problem. So the suddenly throttle opening doesn't allow it to adjust mixture quick enough????


Also, I don't seem to notice any different when I go from half open to fully open on the choke. Should I be noticing a difference?

Apologies for any obvious or daft question, please bare in mind that this is my first experience with a bike, so I'm learning as I go. But so far, loving it!


In regards to pod filter, I'm assume you mean air filter?? I had a look at it and it has the original air box, with a cheapy foam filter inside, all seems clean tho.


I will try take some pictures for you guys so you can see the carb, and I also have some questions about other hoses etc. Maybe someone can kindly label it up for me.


Thanks again for inputs so far

Edited by Sand bags
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Had a very similar problem with 2stroke scooter. A new spark plug did wonders. Still don't know the root cause of the fouled plug but 2months later everything is fine. 7quid fix.

 

I had a look at the spark plug, looked okay, but still have it a clean. No improvements. Maybe I'll just change it anyway.


How would I know if the plug I have now is suitable? 125s generally use the same type, or do they vary with different bikes?

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Had a very similar problem with 2stroke scooter. A new spark plug did wonders. Still don't know the root cause of the fouled plug but 2months later everything is fine. 7quid fix.

 

I had a look at the spark plug, looked okay, but still have it a clean. No improvements. Maybe I'll just change it anyway.


How would I know if the plug I have now is suitable? 125s generally use the same type, or do they vary with different bikes?

 

You should use the exact plug that is specified by the manufacturer. But , yes , they probably are pretty much the same because the vast majority of Chinese bikes of every shape and size use an engine ripped off from the humble Honda CG125.

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You should use the exact plug that is specified by the manufacturer. But , yes , they probably are pretty much the same because the vast majority of Chinese bikes of every shape and size use an engine ripped off from the humble Honda CG125.



Yea unfortunately I don't have a manual with it to get the specs from. I thought I'd be able to find one online easy enough but apparently it's like gold dust lol what spark plug does the Honda use?

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You should use the exact plug that is specified by the manufacturer. But , yes , they probably are pretty much the same because the vast majority of Chinese bikes of every shape and size use an engine ripped off from the humble Honda CG125.



Yea unfortunately I don't have a manual with it to get the specs from. I thought I'd be able to find one online easy enough but apparently it's like gold dust lol what spark plug does the Honda use?


Good morning, ok , its not based on a Honda CG125 , it looks more YBR 125 to me . Anyway , its an NGK CR7E plug but apparently there is a better alternative. See this link , http://zontes-reborn.blogspot.com/2015/03/one-year-on.html?m=1

wp_ss_20181209_0001.thumb.png.8b325b50b01f9a79fc51069f2b84baa2.png

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You should use the exact plug that is specified by the manufacturer. But , yes , they probably are pretty much the same because the vast majority of Chinese bikes of every shape and size use an engine ripped off from the humble Honda CG125.

 

Yea unfortunately I don't have a manual with it to get the specs from. I thought I'd be able to find one online easy enough but apparently it's like gold dust lol what spark plug does the Honda use?


Good morning, ok , its not based on a Honda CG125 , it looks more YBR 125 to me . Anyway , its an NGK CR7E plug but apparently there is a better alternative. See this link , http://zontes-reborn.blogspot.com/2015/03/one-year-on.html?m=1



thanks for taking the time to find that bud. I checked my plug, its NGK CR8E...so i'll give that a swap over and see what happens.

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OK I took some pictures as promised...


Airbox and filter:

 

1386942717_airbox1.thumb.jpg.3516c14da952454bc1cbcdeaa6801da7.jpg

1738834018_airbox2.thumb.jpg.0396d6408431b4b192b05b6ef04c9e5e.jpg

185876967_airbox3.thumb.jpg.81cf4ee3ad2f94adc70c8848e37bba8c.jpg

1738834018_airbox2.thumb.jpg.0396d6408431b4b192b05b6ef04c9e5e.jpg2030410808_airfilter.thumb.jpg.25d3e5b61d27b7109e7b87a17143491a.jpg

 

Spark plug (will order a CR7E asap and try that)


 

461084367_sparkplug1.thumb.jpg.da2dc4627284fc8c40e44a9af663e22c.jpg

1654922800_sparkplug2.thumb.jpg.d37237732135d70ec22b19b16a37a7ac.jpg

 

The mixture/pilot air screw location

1216347681_mixturescrew.thumb.jpg.bb7b95e46bffdac540c18a280ab4c4eb.jpg

 

I wasn't sure what the following things were for, could someone take a look and explain please:

something to do with breathing of the bike?

1915180895_whatsthis1.thumb.jpg.90186ab29c3b271d61cbe02c1a311200.jpg

2011352384_whatsthis2.thumb.jpg.43b967e0aa0d1d681f81b50dd82536d0.jpg

 

and what do these air pipes in this airbox do?

1727966753_theseairpipes.thumb.jpg.58280d1bee6586ab6e8b9032e854156c.jpg

 


thanks again

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sorry pal couldn't see what you were trying to send there! Said file was not found

 

Yeah, I know , it was supposed to be an owners manual PDF.

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What's that ? It's the save the planet , emission control system . Hopefully someone else can explain it better because I've never had a bike with such a device fitted. I believe that the idea is to feed fuel-rich unburned mixture back into the air box when you throttle back . The big bit is probably a reed or butterfly valve. I wouldn't worry about it,I doubt that performance would be effected whether it's working or not .

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sorry pal couldn't see what you were trying to send there! Said file was not found

 

Yeah, I know , it was supposed to be an owners manual PDF.

 

that would have been very handy lol

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I have also just noticed that there doesn't seem to be a gasket on the exhaust manifold?? Is there supposed to be a gap like this?


15445352527101534726930.jpg

 

Looks ok , the gasket is on the very end of the pipe , crushed against the head so you wouldn't see it .

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update.


Changed the plug today, no improvement. Adjusted the pilot air screw afterwards to see if I could improve but still no luck.


here is a short vid...



">

 

Apart from when you opened the throttle really quickly it sounds ok . Have you actually put fresh petrol in it and gone for a decent ride on it ? How long are you warming it up for ? It's fairly cold at the moment so it will take longer . That's why I recommend a hotter plug .

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I have also just noticed that there doesn't seem to be a gasket on the exhaust manifold?? Is there supposed to be a gap like this?


15445352527101534726930.jpg

The gasket sits between the port and the flange on the pipe....so yes, it should look like that.

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