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Head scratching here - running very rich after float adjustment ! CB125s
MIJTEC:
Hi everyone....can do with some advice please ! I am new to working on old bikes but have exhausted all ideas before reaching out to you :)
Picked up a 1975 cb125s recently and after some basic checks and service the bike started. Was running a bit rough but would start by the second kick. All great so far so I thought lets fine tune this further. I purchased a Float level tool to adjust the float height to spec but now its way off the mark when I start it. I'm getting some white smoke and the bike stalls after a minute as the spark plug is totally coked up....it clearly running too rich but I can't see how my minor tweak can make such a difference ? Is there something else I can check that I have missed ? Seems the float height is very sensitive and I cannot get it back to a running condition...or is it coincidently another issue as it was not touched for a few weeks.
Before my clever intervention I had done the following (and the bike was running).
New battery, points and clearance gap set. New spark plug (gap set), oil and air filter, new fuel lines, New petcock and importantly a thorough manual clean of the carb. It was a manual clean with lots of elbow grease and carb spray. I replaced the main jet. All small clearance holes are visible and I've double checked that too. It looks clean as a whistle ?
I am sure this has been asked before (sorry) but can anyone confirm please where the distance should be taken from to measure the float height ? The manual only says carb body but many videos and info online are contradicting this. Some say the gasket seal face which is much further down and the carb body top face which is is higher ? I have taken it from the small notch face on the side of the body up to the top of the float. Spec is 24mm according to the manual. I ensued the float is just touching the float valve spring and not compressing it as advised...please see pics below...looks 24mm to me.. :-\
Also the carb air/fuel screw and idle screw are set to factory conditions. On the air/fuel I have 1.5 turns out from the bottom.
Any other advice/checks to make are welcome....many thanks in advance.
K2-K6:
A very crude observation here...but the float looks very high if I'm seeing that picture correctly.
Evidenced by the "tide" mark on float that looks like its been previously running at a very different angle to how it's now being measured.
Equally crude, rough and ready set method....hold the carb up such that the float is hanging from its pivot vertically downward, then set the height with the tang so that when you tilt the assembly slightly such that the float is resting in its closed position on the valve, that the tide mark/waist line on the float is parallel with the float bowl gasket face.
This is how I set them when lacking good information or to just get them going if no other method available.
Then try running.
K2-K6:
To clarify......perhaps :)
That seam line halfway up the circular float side, use that as measurement reference for your mm setting point and it should then look more logical.
McCabe-Thiele (Ted):
Probably stating the obvious but is the new main jet stamped with the same size as the original.
Replacement brassware is often not as good as the Honda original.
Oddjob:
--- Quote from: McCabe-Thiele (Ted) on November 24, 2023, 04:08:48 PM ---Probably stating the obvious but is the new main jet stamped with the same size as the original.
Replacement brassware is often not as good as the Honda original.
--- End quote ---
I'd mirror that comment but the main jet still looks original, the float valve and idle jet however don't. Aftermarket float jets and seat are well known not to seal as good as original brassware, try connecting a source of petrol to the inlet pipe and see if it actually cuts the petrol off when the floats set at 24mm.
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