QuestionHI was wondering if you could help me.
I baught this old cg125. The bike was Idoling but as soon as you opened the throttle it missed and farted. and so I cleaned out the carb and set it to speck like the manual states, but still it does not run for long and won't rev especially when you open the throttle quikly. I put on another carb but there was no change.
I supect it is the advanced ignition timing. I checked the timing with a light going through the contact (point) and it goes dim when the rotor is on the "f" mark. so I took off the rotor and everything looks good with the small cam that pushes the contact and the legs that fly out when the motor reaches a certain rpm.
Please help I can't think waht else could be the problem.
thanks Ian Runnalls.
AnswerIan, the CG125 wasn't a US model, so have only seen them in photos or ads in the UK sites, still an engine is an engine....
First, get a compression reading. Hopefully, somewhere around 125 psi, I would think. If you are down below 100, then the rings/valves need attention. Check the valve clearances to see if they are correct, as that makes a big difference when the motors warm up and try to run.
The test light should come ON when the points open at the F mark. It sounds like your mechanical advancer is working okay, be sure that it is lubricated lightly on the mechanism cam (internally) and a bit on the points cam surface itself. The spark advancer must spring back when you twist the point cam against spring pressure. The point gap needs to be .012-.014" at the maximum high spot on the point cam, then adjust the points mounting plate until the points just open at the F mark. Could have a bad spark plug cap, perhaps. They generally have resistors in them, at around 5k ohms, measured through the plug cap, off the wire.
Saying that it idles, but doesn't run for long, indicates that it is running out of either fuel or voltage. These bikes must have a fully charged battery and the charging system must be feeding it all the time.
Check the fuel tank cap for venting issues, then investigate the fuel tank itself and the fuel petcock valve for any restrictions. Clean the petcock screen and be sure that the fuel passages are all clear.
Any intake manifold gaskets/O-rings must be sound and leak-free, of course. Usually they won't idle well or at all if there are air leaks there or the idle jet is plugged. You mention changing the carb with another, so it sounds like that is probably not part of the picture.
Bill Silver
www.vintagehonda.com
