Hello guys, I really need help on this one.
Working on a 90cc Kazuma Falcon with a PZ16 carburetor.
So far I have replaced the spark plug with a new NGK plug, adjusted the valves, installed a new direct mount air filter, completely cleaned out the carb (looks brand new inside... jets are clear and all passages flow freely).
new fuel filter, adjusted the air screw multiple times from shut to 3-1/2 turns out, dropped the clip on the needle by 1 slot (1 away from the bottom thus raising the needle up by 1 position compared to stock) And last but not least removed the emissions crap and plugged the tube coming from the cylinder head.
Engine will start and idle perfect even without the choke. But it will try to die if the throttle is opened to quickly. If simply rolled into the engine will run fine all the way to red line, but it will bog or hesitate if you stab the throttle to fast.

Any help would be greatly appreciated!

 

Your symptoms point to a clogged pilot circuit in the carb. but you have covered that. Does it respond better with the fuel screw turned out 3 1/2 turns than it does with it closed?

Plug gap? Blue spark?

 

spark is fine, plug gap is good.
entire carb was taken apart and soaked for a good while. jets were soaked in a mild acid, so they came out looking brand new and completely clear.
I have tried the air screw pretty much every where with no noticeable difference in the bog.
i'm wondering if it simply needs bigger jets now that its breathing better with the direct air filter and no recirculated exhaust emissions crap.

 

If the fuel crew makes no difference I think the pilot circuit is clogged.. it has very small openings .. do you have a air compressor? if so blow thru the fuel screw hole and the pilot jet hole.. this passage must be clear..

On a 4 stroke its a fuel screw the more you open it the more fuel it lets thru) 2 strokes have air screws.

Bigger jets will almost always help a Chinese quad to run better.. they are all jetted insanely lean to pass CARB and or EPA tests..

 

I am 356% positive the jets and circuits are completely clear.

 

ok I believe you.. Then bigger jets are next..


just thought of something.. any chance you have a vacuum leak around the carb and or intake manifold? that would cause a lean condition also..

 

Had this fault on a Honda 300, tried a different carb with no improvement so in desperation tried a new CDI, instant cure!

 

Now that sounds more plausible than anything else I've come up with so far!
I have an extra one laying around I'll try asap and report back to you.
Thanks for all the help!