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Noob Build cg125 - any and all advice gratefully accepted!

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  • Noob Build cg125 - any and all advice gratefully accepted!

    Hi Everyone!

    I'm a long time lurker on here, and thought it was time to upload a little thread of my slapstick attempts at a cg125 (again, i know) cafe/brat/thing that I am making literally in my shed in finsbury park, london. It's my first motorbike and im aiming to start my bike ownership career on what i hope will be a lovely little custom jobbie

    A bit about the bike: original bike is a 1996 CG BR-k (Brazil) which i purchased off ebay for the princely sum of £318 this april as a birthday present to myself. It's definitely seen better days and has accumulated a LOT of rust, muck and god knows what else as it was ragged about a field for many years by a very friendly biking family out in essex.

    A bit about me: I'm an animator and illustrator by trade (i know) but i like to build stuff and tinker. However this is my first attempt at anything mechanical, I dont even have a cbt at this stage haha but not to worry the bike isnt really doing much of anything yet so once i get it running nice im going to get all that sorted out. I am also (like a lot of folks ive noticed on here) a really cheap bastard, so im doing this all with second hand tools, and bits off ebay, making as much as i can myself in the old shed in the garden. So without further ado, here's a few pictures of the bike, and where its at right now:

    Original bike:


    Here it is a little later with me having chopped the exhaust and fitted a new muffler with my £42 clarke mig i bought off ebay


    few process shots of that, the header pipe was way smaller so welded it up a bit with scrap to make it a little wider for the muffler, and fitted a cone filter also:




  • #2
    After much fucking about with the carb due to trouble starting I realised that the petrol tank was so rusty and dented (its a lot worse than the photos make it look!) that rust was blocking the fuel despite pressure washing, electrolysis and much colourful language. So i saw a build i really loved on pinterest that used a honda benly tank on a cg so decided to borrow that idea and got myself a benly tank off ebay for £60 with only a few scratches I'm planning to repaint this later after the frame is powder coated or painted! I also fitted new fuel lines and an inline filter.

    Much to my annoyance i realised after grinding down the old tank mounts that the mounts on the inside of the (sort of) new benly tank werent parralel to each other! not sure if this is a quirk of the benly in particular but was a massive pain in the arse to figure out where to put the new tank mounts! In the end i managed to kind of guesstimate it using a spirit level duct tape and a lot of dark mutterings. Also due to the different mounting aheight at the back i had to weld myself a support down to bolt the rear of the tank on:




    I thought it might also be amusing to anyone reading to see a photo of the only indoor workspace available to me (you wouldnt believe how much a garage costs to rent in finsbury park now )



    • #3
      If I had any advice to give it would be have a clear plan on where or what you want to get to. I went around in circles a little with my first build and spent time and money on stuff I didn't want or later thought I could do it better or different. I am doing another build now and plan to mock everything up first and then strip it down completely before finishing everything off properly and painting. Making a good start and fair play with the shed, I thought I had it bad Good luck!


      • #4
        Hey @Pinky,

        Yeah I've tried to plan as much as i could! I have read loads of threads on here and I often saw people giving this same advice, so I've tried to go in with a plan of what I want it to look like and I think im pretty settled now! I have a pinterest board of bikes i like - attached a few here:





        You'll see there's a definite similarity to these (apart from them all being cg 125's), i love them all ! I really like that tan/cream/blue turquoise color scheme on all these bikes especially with a little splash of red here and there

        I'm currently trying to get the bike running nice and smooth before I strip it down totally and really get stuck into the frame and electrics. I've put new jets in the carb using a guide I found online, but it's currently running really rich, with a lot of sooty black carbon on the spark plug when I pull it out. I think I may have gone too big on the pilot jet - do you know if the pilot jet handles idling?


        • #5
          From what I understand the pilot is the low down, idle and a little further and the main jet is for further up as the names might suggest. That's my understanding, someone else will no doubt chime in and give you a more in depth run down! From what I understand about jets they all have numbers on so you just need to drop a couple points 👍🏻

          PS I like the second one, big tyres 🤣


          • #6
            Hi Bevlak, Looks like you're on your way, nice one. Like has been stated 'fail to plan is a plan to fail' but you seem to have a clear idea of the final result which is a good start. Allow for things to slip and change, but in the main keeping to a style will avoid a hotchpotch of a final bike.

            Cone filter - I wrestled with this issue on my CBX and found, on balance, retaining the airbox on a mid sized 4x carb motor would be beneficial rather than got through the utter PITA swapping out jetsx4 would be. I now have a reliable running bike I can actually ride....yay.

            As per any plan, you need to assess your skills and know where to farm out certain jobs, or skill up? Money is always a factor, but careful purchasing can help too. Also, a realistic outcome regarding final fit n finish is important too. Aiming high to start and then falling short of the finish will see your beloved bike consigned to the parts for sale section as you run out of energy, money, skillz and time.
            My Honda CBX550 project here:!


            • #7
              @pinkys customs:

              Yeah that's how I understand it to re: jetting. Weird thing is I've chopped the exhaust and also added a cone filter, but the bike is still leaving a black/dry/sooty spark plug even with stock size pilot? Weird. Also if I wack back the throttle fast in idle it Biggs and if I hold it there it cuts out.. think my main jet may be too small... I also noticed that when this bogging happens the air from the exhaust goes cold, not sure if this means anything important or not


              Yeah I've certainly got high hopes for this thing haha! I've given myself til next September to have it in good condition to (very slowly) ride to Italy to visit a friend there, so plenty of time to getting looking just right also I am an animator so patience/obsessiveness is something I have in large quantities. My girlfriends patience for the bike is already wearing thin though haha

              I welded the seat loop and hangers for the rear signals this weekend d but phoken died so no pics, will upload photos tomorrow
              Last edited by Bevlak; 25th-09-2017, 10:58 PM.


              • #8
                So last weekend I popped off the back of the frame and welded on my seat loop! Starting to look more like how I had imagined 😁😁 I also welded on some tabs for the rear indicators and gave them a little test fit! Pretty happy with how this has turned out, obviously needs some smoothing out here and there, but think I'm in a good place for welding the battery box now, then a lot of de-tabbing.




                • #9
                  So there's been some progress recently! I've taken the forks off and replaced oil, added the new headlights and pulled off the old guages and added my new shiny round one! Looking a lot more like a proper bike now!



                  I've also welded together a new exhaust hanger as my old one warped like a floppy noodle under the heat of the downpipe!!



                  I'm having an annoying problem with the throttle though, I've found when I pull back the throttle quickly the engine bogs down and if I hold it back, it cuts out! Weird. If I pull the throttle smoothly I don't have bogging.. is this normal or is there a bigger problem?

                  Here's some things I've tried:

                  - Increase pilot jet size

                  - decrease jet size

                  - move needle clip up an down

                  No change as far as I can tell, any ideas guys?? Got a video of it below!

                  Last edited by Bevlak; 8th-10-2017, 03:10 PM.


                  • #10
                    Not familiar with the cj's carb, but there's normally an air mixture screw or a fuel mixture screw. If it's air it would be located on the carb body, manifold side. Really need carb settings from factory, but it would be screwed in carefully until it stops then screw out, say, 2 turns. This screw affects idle up to 1/4 throttle.
                    Really need someone more familiar to confirm. Fuel mixture screw works in a similar way but is located on carb body air filter side.
                    Despite the high cost of living, it remains popular.


                    • #11
                      Hey emsee Yeah I've tried ever setting from all the way in to just about falling out and still have the throttle problem which leads me to believe it's jet sizes that's the issue. I need to get a seat on it so I can take it for a spin and see if it's actually an issue with the ride. If not I might just leave it!


                      • #12
                        Originally posted by Bevlak View Post
                        Hey emsee Yeah I've tried ever setting from all the way in to just about falling out and still have the throttle problem which leads me to believe it's jet sizes that's the issue. I need to get a seat on it so I can take it for a spin and see if it's actually an issue with the ride. If not I might just leave it!
                        Ok. Just a thought though.... take the air/fuel mixture screw all the way out and check the point. It has been known that, if screwed down too hard, the point can break off and block the hole. No amount of adjustment would have any effect if this is the case. Worth checking.
                        Despite the high cost of living, it remains popular.


                        • #13
                          I'm presuming you've swapped the airbox for a pod filter and not changed any jets, it's running weak.
                          I would start by going up 3 or 4 sizes on the main jet,rise the needle one groove from standard, set the airscrew at about 2 1/2 turns out and then report back how it runs.
                          I don't know if it's your exhaust but that engine sounds a bit loud.


                          • #14
                            ive tried upping the jet sizes but soon as i do im getting flooding and its much harder to start - its got all the signs of running lean, (loss of power, a little loud, a little hot) but also a lot of the signs of running rich (sooty plugs, bogging down etc) im super confused about it at the moment! thinking its maybe the timing?


                            • #15
                              hey, i think the best would be put the factory jets in, ride with the air cone, see if its rich lean/ by checking the spark plug after like a 15 min ride. im not sure that the cone changes that much to where you need to change the jets. i have an older cg, and i have always had to ease on the gas a bit, if you go wide open it just wont tick up.

                              keep us posted