Hi Neko,
Long time motorcycle owner, first time china bike owner (just bought one, haven't built it yet) but for what it's worth, I can throw some food for thought your way.
Did the problem start right after switching to the new oil mixture ratio?
A mixture that yields a the dark tan color is what you want I would think. If it was starving for fuel, I think it would be more light tan to white. (After it's well broken in, light tan is ok.)
Plus, in my experience with motorcycles, when a 2 stroke starves, as when it runs out of gas, it will tend to lean out and run about 20% more powerful and rev high for a bit as opposed to losing power. (Same thing if you have an intake leak)
So, if it seems to be losing power until you back off and re-throttle, I might suspect that it's loading up instead of leaning out. (has anyone else found this to be the case, does it seem plausible?)
-Maybe the new oil ratio is the culprit. Revert to the mixture that didn't cause it for a while longer.
-Replace spark plug (simple and cheap...will rule that out before we get into it further)
-Maybe the carb mixture screw can be turned 1/8 th of a turn in, these tend to vibrate out sometimes. (However, looking at mine, this may only have an idle mixture screw so this tip may not apply to this carb, but you could try it easily enough)
-Or maybe the engine is running more efficiently and needs to be leaned out a touch (move clip up one notch to keep needle in jet longer).
Let me know if this makes sense to you (or anyone else- chime in please!)
If you still suspect fuel starvation, I have posted some more suggestions below:
I have heard that the intake gaskets are notorious for failing. Try spraying starting fluid at the suspected areas (mating flange and carb mount) and see if it changes the idle.
Next, Make sure your gas is clean and water free. (Dump out fuel bowl onto a paper towel, check for water, rust etc.) If the problem started after a tank was refilled, maybe some water was in the gas tank you filled it with. Also, sometimes these tanks are manufactured and sent out with major rust and junk in them. If some is found, pull the petcock out of the fuel tank, you should be able to clean the screen and tell if a lot of crap was in there.
If none is found, and everything is clean and flowing to the carb, I can give you some suggestions in the order of easiest to hardest and considering what it's like likeliest to be:
1) I suppose it could be possible (however unlikely but simple to check) that the vent/overflow port is clogged. I'm not familiar with this carb but I've seen some that were just a tiny weep hole that would get plugged eventually and need to be unclugged with a stiff wire. Looking at mine, it has a capped off vent, make sure its not plugged. (must allow air out for gas to go in)
2) Next, I would take it off and blow out the main jet with compressed air. Usually when they starve in the higher revs, it's due to the main jet clogging.
3) If that doesn't cure it, you could try moving the clip on the needle to see if it gets better. If worse, try it the other way. If not better, put it back. Not likely to be the problem since it ran correctly before but easy to do.
4) Less likely but possible, consider that the fuel float may be rubbing against the side of the bowl, causing it to hang up, or it could need to be adjusted to allow more fuel to flow in.
Carburetor pictures how to install and rebuild
Good luck, let us know how it goes. It would be nice to know what eventually fixed it for you so the rest of us can shortcut to the cure.
-Scott
