I am fixing a wk zs125 for my lad and have a couple of carb questions. I have no manual for the bike. It has a Keihin cv carb but struggles to start , needs high tickover adjustment to idle smoothly but then runs fine until high speed when it stumbled. I figured it was running rich so popped on an open cone filter, yes, on a cv carb! It was better, started well, idles better and snappier but still jerky when accelerating up a slip road to the motorway, won't go over 7000rpm as it stumbles. Stopped the bike and saw the end can was very sooty. So I removed the cone filter and ran with nothing, ran beautifully, snappy, idles well, accelerates without hesitation and no high speed stumble.... so do I down size the main jet , fit the cone filter and try to tune it or can I just fit some filter foam over the carb inlet in place of a fitted filter??? I feel that a simple piece of foam cable tied on will work nicely?! In addition I have a vacuum pipe which is connected to the carb and the engine manifold? It's been folded and tied to block it so could this be why the carb stumbles and runs rich? I have no idea why the cv carb needs a vacuum line to the engine? Any ideas?
Chinese bikes tend to always run too lean. Turn the mixture screw to richen it up a bit. Run with an airbox. You will see I run all my bikes with airboxes.
Thanks but a sooty endcan suggests it’s rich? The bike starts and runs better with no filter at all, with the air box it bogs at higher speeds and struggles to start. If I run with no filter then it starts and idles cleanly, accelerates well but feels like it’s lacking power mid range but then doesn’t bog at high speed. As soon as I filter up then it bogs at 7000rpm again. The tuning issue I have is that I cannot find details of the stock jetting sizes, even wk dealers can’t tell me, and it’s not the original carb. I’ve got an adapter for my colortune on order so I’ll try that. Any ideas about the vacuum line question?
Yeah see what the colourtune shows and go from there. Sounds like its been fettled with, the vac probably went to some sort of PAIR system or the likes. (Emissions stuff). Running without a filter is going to suck (no pun intended) over winter...
