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Discussion Starter · #1 ·
Hi there,
I'm having trouble starting my cb 125 k5, namely that it won't start at all.
There's fuel coming out of the left carburator's air intake, it spits it out when turning the engine. Thought it was faulty carburetors so I ordered revision kits and rebuild them both. Except for the floats which seems fine, no leaks.
Now still one carb is spitting fuel and wondering why it's doing that and if this is the reason why the engine won't start.
I haven't checked the float level yet, but wondering if this could be causing the spitting of fuel out the air intake and thus not getting the engine started.

Also reading some things about fuel mixing with oil in the engine due to faulty carb settings and wondering if I could have this problem. I also haven't checked this yet by smelling the oil, but can't do so because I'm not at home for a couple days where my motorcycle's at.

Advice appreciated!
Thanks.
 

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Discussion Starter · #3 ·
So I checked the float levels, they seem fine at about 21 mm.
Now I discovered that one carb doesn't get fuel, and the other is sputtering because it gets too much (?) fuel.
Could this be a petcock issue?
I have a transparent fuel line so I see that one line has some fuel coming out of the petcock but it doesn't continue, as if the carb/fuel tank aren't vacuum so the fuel doesn't run through..
Anyone have any insights in this?
Thanks
 

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Based on my experience the other afternoon, it'll be the float needle valves. Sticking open on one side, sticking shut on the other. Assuming float levels are correct, floats aren't jamming against the float bowl or gasket, and that the floats do actually float.

If petrol flows out of either outlet on the disconnected petcock (pinch either line off in turn), it's nothing to do with the petcock.
 

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Discussion Starter · #5 ·
I just rebuild my carbs so it's got new float needle valves. Could they still be sticking? How does that work?

Just removed my tank and set the petcock to open, fuel came running out of just 1 of the 2 hoses. And strangely enough fuel came out of the house which didn't have fuel running through it while it was still connected to the carb. Now the hose that was connected to the carb that did have fuel coming in doesn't have fuel running through it..
Could it be that the fuel alternates between the two hoses (that would be weird since the carbs both need fuel at the same time?) or do they need to run equally at the same time?

Either way, the screen in my petcock had some gunk in it, so that could be it. Not a lot but some.
I treated my tank with vinegar a couple weeks ago and it has been sitting still with fuel in it (filled to the cap). But now I opened the tank and it has a thick layer of rust everywhere.
So I'm wondering how to treat my tank now. Could the rust be the result of a couple of drops of water that was still in the tank while I poured in the fuel?
Thanks
 

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I just rebuild my carbs so it's got new float needle valves. Could they still be sticking? How does that work?
I fitted some aftermarket ( Keyster ) float needle valves, and they stuck. I can't see why, they appear identical* to the factory items, and worked OK with the float bowls off. As soon as the float bowls went back on, bike wouldn't start, float bowls were empty when I removed them again. Refitting the old items had the fuel flowing again.

Regarding your fuel tap, there has been a lengthy thread on that very issue. In summary, fuel only flows from one pipe, but block that off, fuel flows from other side, and so on. Path of least resistance and all that.

* must be a matter of microscopic difference in tolerances
 

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Discussion Starter · #9 ·

Took my carb off and checked float level again. I didn't measure correctly earlier, as I read that you have to measure from the point where the joint sits. Bit high but not too bad.
What I noticed too is that the float needles of one carb are kind of sliding and sometimes stuck, even though I recently rebuilt it.. so guessing this could be the problem. Had it too with the float needle before this one, so can't install that one again.
Anyone know what helps a stuck float needle? Brake cleaner/WD-40?
 
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