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CG125 Tracker: Ultimate Newbie Build - The Bikeshed Forums

Thread: CG125 Tracker: Ultimate Newbie Build

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  1. #1

    CG125 Tracker: Ultimate Newbie Build

    So, as per the title, I have a CG125, I bought it two days ago at what I believe to be a reasonable price of £285 ,although I'm open to being proved wrong as I did see another build thread with a drunken ebay purchase of £60, so maybe my sober brain has failed me.

    It also came with a Haynes Manual, some WD40 chain wax, a fork seal replacement kit and a motorbike jacket all added in at no extra cost.

    My main inspiration for the direction of this build are the Pride Motors CG125, and Dauphine Lamarck's CG125, pictured below.


    At the moment I have one naff picture from my phone of it sitting in my crowded garage, but it's being moved on the weekend to a more suitable workspace, and I'll be using a little digital camera to get better pics throughout the build.


    So, as for the condition of the bike, I was pleasantly surprised that on the surface, as far as I can tell, it seems to be in great shape considering the price, but it does have some issues which are at the top of my priority list, and, as a complete beginner to anything engine related, I'm trying to figure my first step.

    The main issue with the bike is that, according to the owner (as I haven't ridden it yet, and am also yet to pass my CBT as I did not pass on my first attempt) the bike will get to 45mph and just not be able to get past it, and it'll also stall if left to idle unless you run it for about ten minutes first. So, my plan was to research this issue, get the bike on the centre stand and get to fixing it, but when I got it home to store it I found the next issue.

    The bike's centre stand does not hold the bike up... Basically you roll the bike back onto the stand but the stand doesn't stop when it's vertical, it just keeps rotating past the point that it should and drops the bike back on the floor, and if left to hold it's own weight in this position the bike falls to one side and I'm guessing it'd just fall over but I obviously didn't let it go that far.

    So, at my very first step, I have stumbled. I'm thinking at the moment that I'll try and investigate the centre stand issue, whilst standing the bike on the side stand, so I'll try to take lots of pictures and keep this thread regularly updated, and if anybody has any tips for how I should begin dealing with these two issues I'd be very grateful.

    If you've made it this far then thanks for reading, and I hope to be updating this thread very soon.

  2. #2
    Sounds like the stop has bent or snapped off on the centre stand sure u will see what's a miss when you get down underneath to have a ganders as for the running issues if there is now horrible noises or excessive smoke it will probably be down to fuel starvation at a guess? When I went to the deus shop in Bali they were doing some really cool/different things with cg's

  3. #3
    Yeah, I'm gonna read up on the carburettors on my lunch and try and wrap my head around the air intake system after previous advice, I'll read up on the fuel system after that, thanks.

    The top bike is really well done but not quite my thing, however that bottom one is niiiiiiiiiice! Looks far too complex for a first go with what looks like a custom swingarm, but that is very very nice. I like that retro helmet too

  4. #4
    Take the barrel and head off (very simple, haynes manual very good) and check for scoring on barrel, might be worth while just replacing the piston rings, putting it back together and seeing if it improves the idling.

  5. #5
    Greetings fellow CG builder! Look like you have a good base for a project, and I like your choice of inspiration.

    I'm guessing it's older than '95 so has electronic ignition and there's no points to adjust. It could be you're either not getting enough fuel, or too much air..? Here's a couple of areas to investigate..

    1 - Check the spark plug. Is it white? If so, there's too much air getting into the carb. Replace with a NGK DPR8.
    2 - Open up and clean the carb. Make sure the main jet isn't blocked and everything is in the right place like the float.
    3 - Clean or replace the air filter if it looks knackered.
    4 - Is there a fuel filter? If so replace it.
    5 - Is the exhaust blocked?

    It may be an issue but it'll be a great way to learn about your bike. It seems you are on the right path. I would get the bike running and get used to it before you tear it apart. I wish I had done that before I started working on mine.

    In regards to the centre stand, you could just ditch it like the Pride CG125. It is extra weight and in the words of Colin Chapman - "lightness is good" or words to that effect!

  6. #6
    Wooden Motorycles - Thanks for the advice, I'll add it to the ever growing list of things to check. Again, total newb here but after a quick google I'm assuming you mean cylinder barrel and head. Another thing to look for in the Haynes manual, ta

    Scott_Fury - It's actually a '97, so it has the electric ignition to turn the electrics on, and a kickstart for the engine, if that alleviates your guessing... But, I'm not sure if I'm confused here... Learning on the go here.
    And thanks, I'll go through those 5 points, my first step is to adjust the pilot screw, as per the Haynes manual, to check the petrol/air mixture as that seems like the easiest first step, but, being the easiest step, it will probably not be the culprit, so I'll no doubt immediately be moving onto the rest of the list after that.

    Yeah, that's my current plan, to get it working 100%, and then move onto any custom stuff after that.

    Ha, yeah, I've pondered this but my assumption is that the centre stand will make working on the bike vastly easier compared to only having the side stand, would you disagree?

    Also, I've just realised I've been working my way through your build thread, cringed a bit at the tank drop haha

  7. #7
    With a pre-'95 model you have to adjust the timing of when the spark plug fires, in order to ignite the compressed fuel and air mixture in the cylinder at the right time, mechanically with the points. On yours there's no points to mess with as you should have a little black box, a CDI, that deals with it electronically, so the timing shouldn't be an issue if your CDI is working properly. I'm no expert with CDI's or ECU's but I would imagine it either works or it doesn't at all?

    There's no point adjusting anything if the air filter is knackered and letting through either too much air or none at all, or the main jet is blocked, or the seal between the carb and the engine is leaky. Should be relatively easy to unbolt everything, give it a good clean, replace where necessary, and then you can adjust to your hearts content knowing that it's all as it should be.

    The pilot jet is mainly responsible for the idle and low throttle range, the needle jet controls the mid range and the main jet is for the higher revs. I would guess it's probably the main jet that may need some investigation.

    You can check for any air leaks between the carb and the engine that may be causing the fuel mixture to be a bit too lean (you may be able to hear hissing, but blow out a match and see where the smoke goes, or squirt some WD40 at the join and see if the engine revs pick up. Checking the spark plug is a good way to see what the mixture's like.

    Check this page out for some help on servicing the CG125....


    The centre stand is useful. Mine's stuck fast on the frame so have just left it there, but I may remove it when it comes to painting the frame. Still haven't made my mind up.

    Yep... learning things the hard way. That's what the first build is all about!

  8. #8
    Okay cool thanks, I imagine it's working fine in that case as the previous owner had no issues with starting it up as far as he told me.

    Yeah I guess so, that does make a lot of sense, I'm almost definitely gonna end up taking the engine to bits at some point for all the routine maintenance jobs that are in the Haynes manual anyway.
    So, it has the 45mph issue, so the main jet is a possible culprit for that, but what about it not being able to idle without being ran for about 10 minutes? Is this a normal thing? If not, then would checking the pilot jet not be a good idea? Or are you simply advocating to do that last as there may nothing wrong with the pilot screw but there may be a much more serious issue somewhere else?

    Thanks for the link, that was a really interesting read, used my lunch to get through it. Much easier to read than that bloody Haynes manual too.

    I think I'll get it removed, inspect the damage and make my mind up from there.

  9. #9
    Quote Originally Posted by Kwame-Flip View Post
    Or are you simply advocating to do that last as there may nothing wrong with the pilot screw but there may be a much more serious issue somewhere else?
    Sorry, I should have been a bit more concise. I have a habit of waffling on a bit. I think the point I wanted to make was that the idling and the lack of power may be connected to the same issue, for example it might be to do with the air filter or the mounting of the carb. If so you could adjust the pilot screw, but then find the source of the issue and then have to adjust the pilot screw again.... adjusting it first may make things better but it's just a 'bandaid', it's not fixing the issue at the source.

    Here's a theoretical scenario. When the carb is cold the fuel in the mixture has a habit of sticking to the sides, meaning that there is more air getting into the chamber. So when you start cold the mixture is lean. This is why you put the choke on. It closes a valve which restricts the amount of air, making the mixture richer, until the carb has warmed up and you can then open up the choke valve again letting all the air in once more. Let's say you have air getting in where the carb mounts the engine (or your air filter is missing). This means air is getting in after the carb and making the fuel/air mixture even leaner. It could be the reason why the engine won't idle until it's warmed up, and might explain why the few isn't rich enough at high revs over 45mph. You could adjust the idle mixture and make improvements to the idling, but you would still have the air leak at the carb mount. If you then took it off and bolted it back on and inadvertently solved the issue, you would then have a overly rich mixture and have to adjust the idle mixture again..... phew!!

    Apologies for the longwinded explanation. I hope this helps and not overcomplicates things. At the end of the day it's your bike and you should go about it in a way that makes sense to you. No matter what you do, good or bad, you'll end up more experienced!

    Oh, maybe you could try going over 45mph with the choke on...? If it works it would mean that your mixture is too lean. Although, again, looking at the spark plug should tell you that. The plug is your friend!

  10. #10
    Scott_Fury - The waffling is welcome, I totally agree with you actually. I'm not gonna bother touching the pilot screw until I've checked out all the other possible faults.

    So, progress over the weekend... was slow... but I'm doing what I can as a beginner. On Saturday, my first step was to check the airbox for damage, so I had to remove the seat, then the side panels to gain access. This took me a pitifully long time, but after pissing about trying to find the correct bolts to unscrew in order to get the seat off, I finally realised that my '97 model actually uses 2 latches to lock and release the seat, so, upon finding these I swiftly returned the other two bolts back to their home and took the seat off with a new found ease.
    After celebrating with the seat held in the air like baby Simba, I finally inspected the airbox, but to my inexperienced eyes it seems in great condition. So that's the first possible fault checked off the list.

    My next step was to check the spark plug, for which I needed the one socket my dad didn't have, and seemingly the one socket the entire town of Southport does not stock anywhere, an 18mm spark plug socket. So, while this is in transit from the internet, I moved onto dealing with the centre stand.

    To gain access, I had to first remove the exhaust pipe, which looked like this:
    (File not uploading, I'll have to try again later...)

    Anyway, without photos, this post will be a lot shorter, so, I removed the circlip (not sure if that's the right name) that was holding the pin in place that goes through the frame to hold the centre stand and back brake.
    I then removed the springs that were attached to the centre stand, and the back brake. Here's where I get stuck... I attempted to knock the pin out with a hammer and a block of wood to protect the metal, but the thing will not budge. I'll try again to upload the pictures later, but for now, it's sitting in the garage, soaking in WD40, ready for another try sometime in the week.
    Last edited by Kwame-Flip; 23rd-11-2015 at 08:50 AM.

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