Motorcycle Repair: runs rich, bike cranks, air mixture

Question
Hi Bill,
I wrote to you a while back about my 1974 Honda cb125s. I still have the bike. I got someone to get it running for me. I thought the vales might have gotten bent because the first guy that fooled with it did not have the timing set properly. All that is fine now and bike cranks fine. :o)
Now the problem...We can't get it to lean out. If you put a new spark plug in and crank it, in a couple of minutes the plug will be smut black.  We have replaced everything in the carberator, taken it apart many times, every thing looks fine. The tank has been cleaned and sealed so the gas is perfectly clean. The man who is helping me now is an auto mechanic but owns a old 1952 Harley and has had old Honda in the past. He is pretty familiar with the bikes.
We have adjusted the carb to correct settings and even positioned the long needle valve to the bottom notch to try to lean it out. (the manual says normaly it goes on second notch. We have tried every thing but no luck.
It also idles ok , but stumbles off idle and seems to be loading up when you try to accelerate. Like you have the choke on...
Any advice would be appreciated, I've the bike almost 2 years and have not been able to ride it and enjoy it.
Please help,
Duane

Answer
Duane.... If you are really sure that the carb is cleaned in every passage and is set to specs...
24mm float setting
105 main jet
38 idle jet
3rd notch on needle
1 3/8 turns out on air mixture screw

Then either the float has a pin hole in it and is not "floating" or the bowl vent passage in the roof of the float chamber and vents to the outside of the body is still plugged up, or perhaps the needle jet was left out or is in upside down when you reassembled it all. The needle jet controls the fuel being metered by the jet needle.

I have often seen carburetors blamed when the ignition system was not set up properly, however.

Check the mechanical spark advancer to be sure that it is functioning properly. Then, carefully check the ignition timing after you have gapped the points to .012-.014". The points should just open at the F mark alignment. I am assuming that the compression is correct... 160-175psi with open throttle.
When the points are just opened, stop at the T mark on the flywheel, grab the end of the camshaft (advancer retaining bolt) with some pliers and try to move the end of the cam back and forth. If you can move it more than just a few thousandths of an inch, then the cam bearings are damaged/worn and the head must be replaced or have a machinist install some needle bearings on the cam and in the head to repair this problem.

Make sure that your battery is fully charged to over 6volts, too.

Bill Silver