fouling plugs, bad points?

M

maireeka

Active Member
:mad:

I got the bike (1978 cb125s) to run, even rode it a little. It never really ran right. Now, it will run for a few seconds, a minute tops, and die. When I pull the plug, it's black and wet with gas. If I clean the plug and put it back in, it starts on the 1st or second kick. Without cleaning the plugs, it won't start after it dies.

Could this be related to the fact that i have not yet replaced the points? I set the gap, but that's it.

If it's not an ignition issue, what adjustments need to be made on the carburetor? The idle screw is around 1.5 turns out, the pilot jet (i think that's what it is) is about 1.5 out as well.

thanks
 
Sounds like the carb is dirty. Probably an air passage in the pilot circuit. Also, try a new plug. If the bike starts, the points are working fine.
 
killerdwarf said:
Sounds like the carb is dirty. Probably an air passage in the pilot circuit. Also, try a new plug. If the bike starts, the points are working fine.
Click to expand...

are the air passages in the pilot circuit those two little tiny tubes on the intake side of the carb? they look like they're brass, and they are the only thing that lets air into the carb when the choke is on.

I didn't mention that my choke does not help the bike start, it only starts without the choke. It seems like this might be related if those two tubes are stopped up. Blowing carb cleaner thru the two tubes would fix this, right?
 
Spraying some cleaner in there may help, try it. But I doubt it. You will more than likely have to pull the carbs, dissassemble them completely. soak them, and clean all the little passages with some air. Sometimes the passages can get so solidly plugged that you need to gently, and carefully poke a small peice of wire, (brass is best) from a wire brush. Make sure you pay very close, and special attention to the pilot jets themselves. Those jets have a passage up through the centre like a main jet does, but they also have 4 tiny passages on the sides which can plug up solidly. I use Black Knights asphalt, and concrete diveway cleaner to soak my carbs in. It's a very mild and gentle acid. It cleans up aluminum pretty nicely without damaging it. It is also bio degradeable. I in fact use that stuff for most of my cleaning needs, as I mix it 4/1 with water. For 5 bucks I get 4 1 litre spay bottles of cleaner!
 
The pilot jet is the smaller screw-in brass thingy on the bottom of the carb, right? the main jet is the big one inside the float bowl. The pilot jet is adjustable with the bowls on, if I know what I'm looking at.


I'll take the carb off (again, haha) and pay special attention to the passages and the pilot jet. everything else is clean, since I took it apart 2 times already.
 
The pilot jet will actually be fairly deep inside the carb body, usually in a port right beside the main jet. Look down that port, and you will see the pilot jet. You have to remove it with a small flat screwdriver. Those little ones that are the size of a pen, and clip on your pocket work perfect. You should do a google search on mikuni carbs, and find a diagram of one. Mikuni's are very simple once you understand what you are looking at.
 
My carburetor is a keihin cv, if that matters.

If the pilot jet is covered by the float bowl, then I have not removed it once. That would be my problem.

What is the screw on the bottom of the carb beside the float bowl?
 
I havn't taken keihen carbs apart for many years. I need to do it on my 750 soon. Do what I do when I'm not sure. Google search!!! The internet is a very helpful tool Bud! Find a diagram, or exploded veiw of the carbs, and go from there! Hell, I bet someone else here already has something they can send ya! ;)
 
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