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cg125 2004 won't run unless choke out


cggaz
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hi just got Brazilian cg125 2004 and it won't run without the choke half on(strange-it only fires up with choke off???).cleaned/set up carb,new filter and plug,set valve clearances and still the same,also there's some tippy tapping noises from the engine.i thought it must be the piston tapping and will need a rebore,however when I called the local rebore specialists to arrange it they said it could be a burnt valve???what do you guys think?is there a way to check without the strip down?i've got a week off work in three weeks so plan to take it on then but really wanted to get the parts together beforehand.any advice welcome cheers.

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if you are going to pull it apart for a rebore then why not replace the valves as well if lapped in correctly and new piston the top end of the engine would be like new.have you got a compression gauge that will help determine if valves or rings are letting by,is it burning oil?but needing choke to run sounds like it is running weak or has low compression

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+1 on the compression test before you start ripping it apart!


Have you checked the carb boot is seated correctly and not split? It's easy to check by spraying a bit of carb cleaner around it while it's running.

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Without sounding rude I'd go back over the work you've done. Check you've set your fuel mixture correctly and also re-check your valve clearances if there is now a tapping noise coming from the engine.

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hi again,you know I am a skinflint so don't want to spend money unless I have to .been milling over your suggestion of buying/replacing both valves and piston,that seems best idea for the long term,other options may prove to be a false economy.cheers chaps

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  • 3 weeks later...

hi again,well the plot thickens.just got back from engineers and they say both valves and piston are good and not the cause of the problem.they thought it more likely to be a mixture/ignition issue.checked intake stub and it's machined aluminium with no sign of damage.does anyone think it could be related to the pair valve system,if so how would the bike run without it?any suggestions advice or pity welcome thanks

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tapping noise would suggest valve clearance I would have thought. running on half choke Will damage the engine. when it's warmed up are you saying it stalls then or just cold? never touch the fuel mixture. if you have tighten it right up then do a quarter of a turn till the engine runs without choke.

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hi it seems I was over reacting to the noise apparently these are noisey by nature due to the push rod set up.got the mixture screw at factory setting.it will only run with choke half on even when warmed up if you knock choke off it cuts out.my next effort is to replace the wierdo air valve system,thinking that maybe the valve is stuck open,after that I'm out of ideas,thanks

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OK - Some missing information?


Does it cut out with 1/4 throttle applied and then choke off?


If NOT - Then it is likely to be the mixture. Hold 1/4 throttle (with choke off) and turn mixture scew (slowly) either in or out (50:50 choice). If revs climb, then back off throttle carefully and continue adjusting the screw in the same direction until revs start to dip, back up a touch and it should now be OK. If revs don't change, then turn the screw the other way.


If Revs peak but don't then dip even with the screw either fully in, or fully out, then you have either a fuel restriction (check filters, carb settings) or an air problem (check filters, gators, etc.).


:cheers:

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  • 2 weeks later...

hi again finally got it solved,firstly tried everything you guys kindly advised-but none of it worked.ran it round to a friend's to see if he could help.turned out he had an old style cg carb.it dropped straight in and the bike is running sweet as a nut,plug colour is great too,now I'm a happy bunny.due to all the work I did trouble shooting the motor it should last way longer too,thanks again guys.

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  • 2 years later...

hi ok got a new problem now.building cg up from couple of damaged repairables.engine and loom I'm using is from a bike I had running when I bought it.however when I've come to rebuild it and set the wiring up I can't get the lights(head,tail,meter)from the yellow wire leading from the reg/rec but they all work(and all switches)off the black live wire from ignition switch.so I know all switches and conponents work but not off yellow wire-tried another cg reg/rec I have still no joy-I'm going nuts!!!!help

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