GT125R 2008 High Idle
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Bike Model = : GT125R 2008
Hello, hopefully someone here can help me.
I bought a 2008 GT125R as a project bike. When I first got it, it hadn’t been on the road since 2012. It did run, but it had a very high idle.
The first thing I checked was the carburetor and intake manifolds, which were both in bad condition. The manifolds were ruined, and the carb was badly rusted. Because of this, I bought a used replacement carb and new intake manifolds.
After fitting the new parts, the bike still idles very high, around 4,500–6,000 RPM.
We’ve checked for air leaks around the manifolds but couldn’t find any. I adjusted the idle screw, which brought the idle down from about 9,000 RPM to its current range, but it won’t go any lower. I also tried resetting the fuel mixture screws, but that didn’t make any difference. The throttle cable and throttle action also seem fine.
Does anyone have any idea what could be causing this?
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Remove the throttle cables and choke cables
Can you rev the bike manually by hand ? and does the RPM needle come down FAST or SLOW or just hang about for a bit then slides down ? etc…
If not sure ===> Go to youtube , upload a video and select it as “UNLISTED” so no one finds it on youtube , then copy the SHARE LINK paste it here.
Dont set it to “private”
This lets us see what is happening, don’t be afraid if its a 3 minute video (10 second videos suck as they dont help make a proper judgement)
Remember = High revs on CV carbs usually means illegal air is still entering or carb is “hunting” for fuel (carb internal issues) or exterior parts (moving cables or choke assembly rail on the carb jammed etc) are still activating the carb to allow more air than usual.
Put mixtures back to 3 Turns out FRONT and 3 + 1/4 Turn out rear, this sets the baseline.
Jetting Tutorial = Click Here
SLIDE needle tutorial = Click Here
Did you change the Intake O-Rings ? They are a big deal than you think, click here
Airbox missing? = Carbs will behave rough, make sure airbox is on and is fully swallowing the front carb as it can peak out.
Get a fresh set of CR8E plugs from halfords . Buy a pack of 4 (2 for test ride) and 2 for emergency
Come back , upload pictures of your plugs on this forum , we gotta see inside the plug and the threads, this will tell us the mixture from idle all the way to 3-4th gear riding down your street.
I said a lot, but please, take your time. 1 thing at a time, so you can see its mood change gradually till you find the culprit.
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