Idle Jet Mystery

[jeffwah]

I have a 139QMB 50cc w/ free flow air filter. After destroying the carb on my first attempt to clean a carb, I replaced it and ever since I've had a idle jet mystery. The idle jet that came with the new carb was way too small. I had to unscrew the air/fuel mixture screw almost completely out just to get the scooter to run. So I started buying and trying new idle jets: #31, #32, #34, #35, #38. Even with the largest jet, I'm still having to turn the air/fuel mixture screw about 6 turns out... almost to the point that the screw spring barely keeps it in place. Also, with the screw completely unscrewed, I can not get the idle to stumble or the bike to stall like I expect. So what's up?

Should I buy yet another idle jet (#40)? My carb was suppose to a standard replacement for 50/60cc, but is it possible that the new carb is larger than I expected... too large for my 50cc... so I'm getting too much air flow? I have some foam which slips over my air filter... it "should" restrict air a bit (and keep more dust out)... should I try that before messing with jets?  Maybe the auto choke is defective?


FYI - Also I've had a main jet mystery too... here is my progression on those jets: #78, #80, #82, #85, #88, #90, #95, #92. I think it's crazy that I'm having to run #38/#92 without any other major upgrades other than a free flow filter and a new carb (which might be larger than I expect).

Thanks for your thoughts.

A few more details:
Needle clip low position (richest)
Orange performance CDI
Intake Valve: .004"
Exhaust Valve: .004" (slight tick, best speed so far)

[katastroff]

Sounds more like an air leak. If you tried all those big iddle jet and still get the same results, i would look somewhere else. Cracked intake/ intake spacer maybe? Or not properly bolted on?

[humanshield]

The post above has good advice.
You can measure the opening on the engine side of the carb.  It should be 18mm (inside)
I don't know if you're familiar with this but it can also help visualize the problem.