Hello from Germany, work on it til it runs – GV125M E3 2007 Carby
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Bike Model = : Hyo GV125M E3 2007
Hi everyone,I got my motorcycle license last year, and this 2007 Hyosung GV125 is my very first bike. It had only around 5,500 km (about 3,400 miles) on the clock when I bought it, but because it spent so much time sitting, I believe many of the components were still the original parts from 2007.
Not long after buying it, I started having some issues. The bike would stall after riding for more than about 30 minutes, and it would occasionally start hesitating and jerking while riding.
The first things I replaced were the ignition coils and the regulator/rectifier. I bought both from AliExpress. The ignition coils had different wiring than the original ones, so I had to rewire them, but that wasn’t a problem. The bike already ran a little better afterward.
Next, I replaced the spark plugs with iridium plugs from my local motorcycle shop and installed new spark plug caps that I bought from a member here on the forum. Again, the bike improved.
Interestingly, the original problem has now changed. It no longer stalls when the engine gets hot. Instead, after riding at around 100 km/h (60 mph) for a longer period, it starts to hesitate slightly and eventually loses power. The throttle test seems to indicate that it’s suffering from fuel starvation.
Because of that, I turned my attention to the fuel system. I cleaned the fuel tank twice because there was quite a bit of debris inside. I completely removed, disassembled, cleaned, and reassembled the fuel petcock. While I was waiting for the tank to be empty, I replaced the fuel filter and cleaned the fuel cap. I also replaced all the fuel hoses from the petcock to the fuel filter, from the filter to the fuel pump, and from the fuel pump to the carburetor. While I was at it, I replaced all the vacuum hoses going to the fuel pump to eliminate the possibility of vacuum leaks.
Unfortunately, the problem is still there. I’ve now ordered a replacement fuel pump, a new air filter, and a new chain and sprocket kit from members here on the forum. I’m hoping the fuel pump will solve the issue, as I suspect the original one is simply showing its age.
If anyone has experienced something similar or has any ideas about what else I should check, I’d really appreciate your advice.
I’m happy to be part of this forum, and thanks in advance for your help!
Please move if I targeted the wrong forum section.
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This sounds crazy but have you seen the tutorials on the forum on how to carefully remove the airbox , then you can access the carbs to give them a much needed ultrasonic clean
Then check what jet sizes are still in the carb ?Β Also we don’t know if the float needles are still working properly , these floats control how much fuel you can get , if it gets too low before the pump can send more fuel, you will feel like its running on a dry tank then cuts out.Β It wont start until you crank it multiple times , then it works (cranking was filling up the carbs again)
So maybe our next battle should be the carbs
Good job replacing everything else,Β it just means you are serious about giving it more life , some people just abandon it which is a shame.Β Β From what you said, it sounds like we should deal with the carbs and also double check the rubber pipes for any damage and replace O-RINGS which sit inside the rubber pipes
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I already inspected the carburetor once beforei got suspicious of the electric parts. The carburator looked clean. But I didn’t inspect the needles. That was before I found this forum.
I want to make sure that the fuel pump works correctly before I have to disassemble the carburator again. The last time it was pretty hard to fit it in again.
And yeah, since I found out about this forum I read a lot of posts here and yes I want to switch the main jets in the carburator but like I said, I wanted to make sure the pump works properly.
I make my analytics with ai and reading in this forum to get rid of all the failures that occurred. Works pretty good so far. When the new parts arrive I will make more photos of what I’ve done.
What rubber pipes and o rings do you mean?
And yeah I love this machine π
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Mikuni vacuum fuel pumps can be disassembled, cleaned and assembled. Most likely you will find some dirt inside. Nevertheless if the bike runs “okish” but sometimes fails to start on the first crank and holding open throttle over a long period of time triggers a progresive loss of power, you might try to add some clenaer to the fuel. It will most likely improve it to some degree, it might take a looooong time and many refuels and most likely it will never reach 100%. Otherwise you’ll have to do what M77 suggests you, carburetor cleaning off the bike and adjust them when reinstalling.
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I already put in a carby cleaner two consecutive times. And my only problem now it’s the loss of power when I ride at maximum speed for a period of time. The period is longer if the tank is full and shorter the less fuel I have left. It feels like the carburator runs dry.
So my guess is the membrane in the pump is too old to make the full stroke. It’s easier for the pump when the pressure is high from a full tank. That’s why I look at changing the fuel pump.
I tried to look for a new membrane but it’s costs as much as a new pump because I would have to import it.Β o.o
Keep you updated when I changed the parts.
Packet should arrive on Tuesday.
=)
Thx for all the suggestions.
Maybe I try another cleaner after changing the pump
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What rubber pipes and o rings do you mean?Β
Pipes = Sorry i meant the intake manifolds (which hold the carbs down to the cylinder heads) , so they also have o-rings in them, so if one of them got deformed during re-install or are too old , you could have a micro leak that has made the vacuum system weaker.Β Also make sure both front and rear intake pipe share vacuum to open the fuel pump.Β Β (2 intake pipes feeding the vacuum pump in a shared T-Junction (T-Piece) = better chance of fuel flow)
If you see any egr parts (ais parts) get rid of it,Β your vacuum system will thank you, look here:
[How to Tutorial] AIS Removal Guide – Hyosung GV125 GV125C (EGR Blank Kit Fitting Guide)
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What rubber pipes and o rings do you mean?
Pipes = Sorry i meant the intake manifolds (which hold the carbs down to the cylinder heads) , so they also have o-rings in them, so if one of them got deformed during re-install or are too old , you could have a micro leak that has made the vacuum system weaker. Also make sure both front and rear intake pipe share vacuum to open the fuel pump. (2 intake pipes feeding the vacuum pump in a shared T-Junction (T-Piece) = better chance of fuel flow) If you see any egr parts (ais parts) get rid of it, your vacuum system will thank you, look here:
[How to Tutorial] AIS Removal Guide β Hyosung GV125 GV125C (EGR Blank Kit Fitting Guide)
ah… Thx for enlightening me π
I guess when I install the bigger main jets I could just swap them.
But I think I don’t have an ais system.
I read the post you mentioned but to follow this guide I would need more photos. I don’t know what he is up to in this guide, something like turning off the ais…
But I’m no mechanic and I don’t know all the parts that are mentioned.
But replacing the manifolds, that’s something I am capable of
Thanks again
π
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