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125cc ALMOST there...


WillingampUnable
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Hi all - I'm guessing this is asked all the time but after having serious issues with my 2008 GN125 I'm almost there...I think.


The bike came with a knackered carb (fuel mix screw minced down tight and no pilot jet) so I bought a Chinese copy. Turns out there were small differences between the two so I've managed to use all the parts from about 3 old mikunis to get it back to stock. The bike runs better than it ever has but is stumbling on the pilot circuit and has black sooty plugs.


From the googling I've done I'm guessing this is running rich and despite playing with the air/fuel settings can't get it right. What would be best to try first - adjust float levels, needle height or put a smaller than stock pilot jet in it?


It also seems to be slightly struggling in high revs and WOT (can't get it up to 50mph) so may need an adjustment here too unless the float height is also causing a rich mixture here too (but it could also be my valve clearances or something else I've played around with). Anyway - will cross that bridge when I come to it!


Any advice on my next best place to start is much appreciated!!

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My advice:


1. Say hello in the Newbies thread.


2. Put your location (town will suffice) in your profile.


3. When you get an answer from a fellow forum member - remember to say 'thanks'.


OK - Obviously running too rich. Probably needle settings / jet settings / mixture incorrect. But, could also be timing / clogged air filter.


:cheers:

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My advice:


1. Say hello in the Newbies thread.


2. Put your location (town will suffice) in your profile.


3. When you get an answer from a fellow forum member - remember to say 'thanks'.


OK - Obviously running too rich. Probably needle settings / jet settings / mixture incorrect. But, could also be timing / clogged air filter.


:cheers:

 

Hmm feel the need to apologise for my own forum ignorance. I’ll keep it brief. Sorry for the lack of introduction, didn’t understand the form.

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...Hmm feel the need to apologise for my own forum ignorance. I’ll keep it brief. Sorry for the lack of introduction, didn’t understand the form.

 

All forums are the same and suggest that newbies introduce themselves as a matter of courtesy. It is also immensely helpful to put your general location in the CP so that help can be tailored to the location.

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Apologies - time was of the essence. Very new baby and bike needs to be running so the missus can have the car!


Didn't realise the location thing as there's absolutely NO way I'm spending more money at local garages as I'm at least £600 down on what this thing is worth :shock: but I'm in Leeds - will update my profile!


I assumed it was running lean due to the RPMs dropping below idle before recovering so altered the needle and went back to stock pilot jet. Also set the mixture to stock. Just had a test run and seems to be running OK with no bogging down from idle to 1/4 throttle anymore. It still doesn't want to go above 40MPH but I'm 6ft3 and 17stone so not expecting to break any speed records. Although when I had a vanvan a few years back I definitely managed 70MPH laid flat on the tank going downhill with the wind behind me :D


I put a new sprocket set on a while ago and I think the front sprocket may have a different number of teeth to stock so might tinker with the steering ratio.


Clearances seem OK now, very slight tapping but this gets better as it warms up and I checked the chain tensioner. I think the rockers etc are worn but I don't wanna start opening up the engine block when all it needs to do is get me 5miles to work and back.


I'm gonna see how it runs this next week and hopefully won't spend the entire time thinking "I should've got a keeway on finance" the entire time.


Thanks all!! Sure I'll be back on at some point for advice because I do love tinkering with it...

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When you say it does not want to go above 40MPH - Is that in both the top two gears (i.e. the same top speed 'limit') or, just in top and you can exceed 40mph in 3rd / 4th?


Can you 'red line' in any gear?


Is the exhaust smokey?


Have you checked / cleaned the air filter and fuel filter?


:scratch:

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Got it to 45mph this morning in 5th - I can't get above 40mph in 4th without the engine seeming like it'll explode! Not vibrating that much but feels like it's going way too fast for comfort. This might sound daft too but the bike smells HOT after a 15min ride. The exhaust isn't red hot but it's so much different than my old VanVan.


Can't red line it - hits 4-6000 RPMs tops I think (tried keeping an eye on it this morning, will check again tonight). Dread to think what it would be like any higher.


Exhaust doesn't seem smokey at all - perhaps there's sometimes a slight pop to the exhaust but nothing noticable.


Fuel filter and air filter are both brand new. Mechanic I had out to look at the bike when it was a none runner said not to bother oiling the filter as I RUINED the last one with some sticky spray stuff which stopped all airflow. Might be another reason it's a bit lean? Or rich :(


The slight bogging from idle has returned this morning but much less noticable than before so maybe further tweaking is required!


Cheers! James.

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