Idle and fuel leakage issues on my Derbi Cross City 125

641 Views 9 Replies 2 Participants Last post by WintrSol, 10 mo ago

Tom_NnnB

Discussion Starter · 10 mo ago

So, not too long ago my bike has started to develop some problems after running perfectly for around 2k kilometers. I've recently noticed that after a few minutes of riding and when stopped at a red light or just idling my bike shuts off, which wasn't a big deal, but that was just the first of the symptoms. Now, when the bike randomly shuts off while idling it also starts leaking fuel out of the overflow hose and becomes impossible to start. The only changes i've made to the bike itself was that I installed an aftermarket exhaust (fake, derestricted Akrapovic). I've replaced the carburetor with a new stock one (Naraku PZ26), checked out the one I had issues with and didn't see any problems.

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WintrSol

· #2 · 10 mo ago

Sounds like the float chamber is overfilling, essentially choking the engine to death. Could be a bit of grit in the float valve, or the valve is shutting off too late.

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Tom_NnnB

Discussion Starter · #3 · 10 mo ago

Yeah, I thought so too, but the carburetor was literally changed two days ago, and the problem persisted, so I thought maybe the problem would be something else. Nevertheless i’ll double check the carburetor later today.

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WintrSol

· #4 · 10 mo ago

Dirt coming out of the fuel tank can make any float valve leak; got a filter in-line, not just the petcock screen?
Also, just because the carb is new doesn't mean it is adjusted. If you have a bowl drain that can have a clear tube connected to it, turn the tube up along side the carb and open the bowl drain - if the fuel rises to the bowl/body sealing surface, the float isn't set, or the float valve is leaking. You can test for a leaking valve by closing the petcock and draining the carb, then check the level again by opening the petcock with the tubing connected. It should rise and stop, but if it is leaking, it will slowly rise above the set point.

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Tom_NnnB

Discussion Starter · #5 · 10 mo ago

So i have an in-line filter from my gas tank to my carburetor, so i don't believe any debree could have gotten in. I also checked and the float is seating well (I attached some pictures) when the float is hanging fuel leaks, but when it is pressed up (if we're imagining that the float bowl is the bottom side) , the valve seats and nothing leaks. I also took out the float needle itself and when I apply pressure with my finger in the hole which the needle is supposed to be in, fuel doesn't leak, and when i take my finger off,
fuel leaks. So i believe everything checks out and the valve seats just fine.

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WintrSol

· #6 · 10 mo ago

So far, so good. Picture of the bowl? If it has a drain you can connect a tube too, you can measure the fuel level. Do you have manual or data sheet that says what it should be? There is only one value for this, and it should specify the float height or fuel level (or both), and how to measure it/them.

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Tom_NnnB

Discussion Starter · #7 · 10 mo ago

Yeah, my bowl has a drain, followed a youtube video and did the clear tube test, seems to be fine. Also tried to find an informative owners manual on the Derbi Cross City 125, but to not much luck, so I checked out similar bikes like (Derbi Senda SM 125 and Derbi Terra 125) and in both of the manuals the float is supposed to be parallel with the base of the carburetor so that also checks out. I have recently noticed that sometimes fuel leaks from my petcock also (where you turn the tab to ON, OFF, or reserve), but I doubt that could be the problem?

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WintrSol

· #8 · 10 mo ago

I guess it depends on how the fuel line is routed; gas can find a way to follow surfaces, which can hide the actual leak. A longer fuel line in the shape of an S on its side should let any leaks from the petcock drip so it doesn't seem to come from the carb.

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Tom_NnnB

Discussion Starter · #9 · 10 mo ago

Yeah I thought similarly, but when gas leaked from when my bike used to stall you could see the gas come out the overflow, but these past few leaks/drips are very obviously just coming from the gas tank petcock. Either way I wouldn't assume if it did leak from here (attached photo) that that would cause any problems with the carburetor. Which i'm quite stumped about, considering everything in the carb checks out and yet it still sometimes overflows.

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WintrSol

· #10 · 10 mo ago

Well, if the float height is set correctly, I think that leaves a sticking float valve, which could come and go. Or, a crack in the overflow tube.

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