139QMB 80cc BBK Install Issue

jbmsu · 09-24-2022, 11:15 PM

I have a basic scooter rig with a 139QMB 4-Stroke. I rebuilt the engine with new gaskets, CVT clutch & band, variation w/ 6.5g roller weights.

I used the ATMT1-008 Glixal 47mm BBK, and added a cone cold air intake.
The stock carb is 18mm and originally had a 30 pilot jet and a 78 main jet.

The valves were adjusted to .004

More details below.

jbmsu · 09-24-2022, 11:18 PM

After startup and brief break in, the bike won’t start without the AF screw being like 5-6 turns out, runs great until 5-6k rpm and turns hesitates and backfires, bogging down and dying at WOT. It has a max rpm of about 6.2k, although it should be much higher.

I swapped the jets to a 33 pilot 92 main, and absolutely nothing changed. I also checked the float needle. No clue which way I should be going.

Thach2264 · 04-24-2024, 05:07 PM

I am having somewhat same issue with 80cc for my Piaggio Typhoon. When give throttle it bogged and died if I don't let go of the throttle. Have changes main jet to 98 and back down to 88, still bogged. Sometimes it would rev/throttle as it should then back to bogging again. It idle great though with size 35 and needle is at most top. I am about to tap out on this.

09-24-2022, 11:18 PM	#2
jbmsu Join Date: Sep 2022 Posts: 2	After startup and brief break in, the bike won’t start without the AF screw being like 5-6 turns out, runs great until 5-6k rpm and turns hesitates and backfires, bogging down and dying at WOT. It has a max rpm of about 6.2k, although it should be much higher. I swapped the jets to a 33 pilot 92 main, and absolutely nothing changed. I also checked the float needle. No clue which way I should be going.
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