China scooter surging, what's up! it's pretty nuts.

I recently made the stupid mistake of fixing a Chinese scooter we got for free, qmb139 "gy6" 50cc. It reinforced why folks distrust those china motored things. so much wrong. it still doesn't run right despite fixing SEVERAL smoking guns and replacing EVRYTHING.

Had to replace the tank and petcock off the bat, rust city.

Then was the carb - just wrecked but that was from a year or 2 of neglect, and a whole new one was 20 bucks shipped. had it almost cleaned except the accelerator pump, and wasn't confident on the idle.

It'd idle fine and run to about 20-25 and then just start surging, like someone flicking the light switch on and off. rev die rev die rev die. about 1 second cycle. I thought it was jetting and clogged jets so I got the new carb, slapped it on, still only went 20-25 surging. checked the variator and that's all good, variates fine and isn't surging from the vario. figured valves maybe were bad and then hoke just ordered a whole kit for it. head cylinder valves rockers CDI, ht coil, new intake- everything, even belt and variator weights for $80 shipped lol.

The only thing it didn't have was the spacer under the carb which it turned out was cracked out and airleaking massively. Figured that musta been the problem, but with the spacer replaced and whole new top end it runs EXACTLY the same. surging on/off as soon as it hits 20-25.

Played with jetting from 70 to 95 Also played with airbox and pipe, the jetting affects how it runs but in all cases it'd still get either sputter or boggy or whatever it'd hit 20ish and start surging on and off. it's like a 1 second cycle.

So I replaced the CDI and coil and plug and still exactly same. THEN! I noticed the pickup for the CDI trigger had a broken bolt! I fixed that bolt and still no change. but then noticed the pickup itself looks cracked so I just ordered a new stator and pickup. not arrived yet

So:

*New gas, tank, lines and filters

*New CDI, coil and plug

*new 80cc cylinder, head and valves, neatly set and timed

*New intake, carb and gaskets, jetted from 70-95, now "best" at 85

It runs exactly the same as it did with a clogged stock carb, broken intake gasket, loose valves and a broken intake pickup. Exactly. the. same.

Any thoughts? I've had fun seeing if my diagnoses match the MA OT on other vehicles, whattaya got?

Re: China scooter surging, what's up! it's pretty nuts.

It’s probably got the roro.

Pickup sounds likely. I’ve had a number of “wtf, I’m gonna burn this damn thing and send it back to hell where it belongs!” hard to diagnose issues on a few bikes in the past year that in every case have been some ignition component getting inconsistent without totally failing.

Re: China scooter surging, what's up! it's pretty nuts.

Verify that the Vacuum line to the petcock is good and solid. If it is not it will starve the engine of fuel at speed.

Re: China scooter surging, what's up! it's pretty nuts.

Oof yeah put it on FB for 200 bucks and get rid of it

Re: China scooter surging, what's up! it's pretty nuts.

Traitor

Re: China scooter surging, what's up! it's pretty nuts.

Pushrod Fifty /

Does it need battery voltage to run, if so, check for voltage spikes.

Re: China scooter surging, what's up! it's pretty nuts.

> live ɘvil Wrote:

> -------------------------------------------------------

> Traitor

haha, perhaps more apt - "know your enemy"

I have fixed dozens of these things, usually it was someone related to our bike co-op or someone mistakenly stumbling onto the swoops needing help, the atl vespa shop our buddies owned and bobby & brooks worked out would sometimes send the junk bikes to me cuz i'd do it. i mean i know these things, i enjoy tinkering with stuff and helping folks usually.

And yea, the petcock vacuum line was a great suggestion cuz man of all these things i've worked on that's been #1 most common by a longshot. and then the other common stuff like carb and plug.

But this things got a gravity fed fuel now, it's got no problem flowing or filling. the vac bung's sealed off. maybe it needs a positive fuel pressure? I dont think thats real tho, never seen that and it's a petal valve not a pump. Still great suggestion cuz man that's a regular issue.

Re: China scooter surging, what's up! it's pretty nuts.

> Pushrod Fifty Wrote:

> -------------------------------------------------------

> Does it need battery voltage to run, if so, check for voltage spikes.

This was a thought I had last night, I hooked up a battery and no change, but then realized the ignition switch wasnt working to put power to accessories. I hotwired it to bypass the ignition switch since that was a clear issue, thinking aha! gotcha this time, but nope, no change. except that now i can electric start it and the lights work somewhat better.

I've never had one that needed the battery but there's plenty of weird differences and variations.

Re: China scooter surging, what's up! it's pretty nuts.

Check the gas cap vent too. Try it without the gas cap?

Re: China scooter surging, what's up! it's pretty nuts.

Overpriced Parts /

> Born to be WillD Wrote:

> -------------------------------------------------------

> > Pushrod Fifty Wrote:

>

> > -------------------------------------------------------

>

> > Does it need battery voltage to run, if so, check for voltage spikes.

>

> This was a thought I had last night, I hooked up a battery and no

> change, but then realized the ignition switch wasnt working to put power

> to accessories. I hotwired it to bypass the ignition switch since that

> was a clear issue, thinking aha! gotcha this time, but nope, no change.

> except that now i can electric start it and the lights work somewhat

> better.

>

> I've never had one that needed the battery but there's plenty of weird

> differences and variations.

Will, you your choice in bikes are about the worst I’ve ever seen!

You must like suffering!

Re: China scooter surging, what's up! it's pretty nuts.

> Born to be WillD Wrote:

> -------------------------------------------------------

> > live ɘvil Wrote:

>

> > -------------------------------------------------------

>

> > Traitor

>

> haha, perhaps more apt - "know your enemy"

>

> I have fixed dozens of these things, usually it was someone related to

> our bike co-op or someone mistakenly stumbling onto the swoops needing

> help, the atl vespa shop our buddies owned and bobby & brooks worked out

> would sometimes send the junk bikes to me cuz i'd do it. i mean i know

> these things, i enjoy tinkering with stuff and helping folks usually.

>

> And yea, the petcock vacuum line was a great suggestion cuz man of all

> these things i've worked on that's been #1 most common by a longshot.

> and then the other common stuff like carb and plug.

>

> But this things got a gravity fed fuel now, it's got no problem flowing

> or filling. the vac bung's sealed off. maybe it needs a positive fuel

> pressure? I dont think thats real tho, never seen that and it's a petal

> valve not a pump. Still great suggestion cuz man that's a regular issue.

I still love ya man!

Re: China scooter surging, what's up! it's pretty nuts.

> Thomas TPRF Wrote:

> -------------------------------------------------------

> It’s probably got the roro.

>

> Pickup sounds likely. I’ve had a number of “wtf, I’m gonna burn this

> damn thing and send it back to hell where it belongs!” hard to diagnose

> issues on a few bikes in the past year that in every case have been some

> ignition component getting inconsistent without totally failing.

^mmm hmmm!

Re: China scooter surging, what's up! it's pretty nuts.

♣Slew Foot♣ /

Lot of them have an alarm and key fob tied right into the ignition very specific to model and stator chip.

Xtra problems can't be hardwired.

Re: China scooter surging, what's up! it's pretty nuts.

well, im watching this with interest.

im aboit to post all the cool cheap chinese stuff im getting saturday for my African CG clone.

when I limped it onto base, it was surging all over the rpm and load range.

i thought maybe it didnt even have a float in the carb it was so bad. like, i could just get a spray bottle of gas to shoot at the intake w/o a carb and get similar performance.

I’m being dramatic. Still, I’ll post up in my thread and chime in here if I find something.

Re: China scooter surging, what's up! it's pretty nuts.

> Overpriced Parts Wrote:

> -------------------------------------------------------

> > Born to be WillD Wrote:

>

> > -------------------------------------------------------

>

> > > Pushrod Fifty Wrote:

>

> >

>

> > > -------------------------------------------------------

>

> >

>

> > > Does it need battery voltage to run, if so, check for voltage

> spikes.

>

> >

>

> > This was a thought I had last night, I hooked up a battery and no

>

> > change, but then realized the ignition switch wasnt working to put

> power

>

> > to accessories. I hotwired it to bypass the ignition switch since that

>

> > was a clear issue, thinking aha! gotcha this time, but nope, no

> change.

>

> > except that now i can electric start it and the lights work somewhat

>

> > better.

>

> >

>

> > I've never had one that needed the battery but there's plenty of weird

>

> > differences and variations.

>

> Will, you your choice in bikes are about the worst I’ve ever seen!

>

> You must like suffering!

You're uncharacteristically correct this time

I run with whatever I stumble into. I've got a CR80, an Aero 125, this Chinese scooter and an old fanticXKE all free piles of junk and all slowly making their way back to functional. That fantic came from you! and agreeably, at least at present, is the best of the bunch. It's got a trac motor on it now tho - because that was also free, and because yea, I guess part of me does like suffering

Re: China scooter surging, what's up! it's pretty nuts.

> Born to be WillD Wrote:

> -------------------------------------------------------

> > Overpriced Parts Wrote:

>

> > -------------------------------------------------------

>

> > > Born to be WillD Wrote:

>

> >

>

> > > -------------------------------------------------------

>

> >

>

> > > > Pushrod Fifty Wrote:

>

> >

>

> > >

>

> >

>

> > > > -------------------------------------------------------

>

> >

>

> > >

>

> >

>

> > > > Does it need battery voltage to run, if so, check for voltage

>

> > spikes.

>

> >

>

> > >

>

> >

>

> > > This was a thought I had last night, I hooked up a battery and no

>

> >

>

> > > change, but then realized the ignition switch wasnt working to put

>

> > power

>

> >

>

> > > to accessories. I hotwired it to bypass the ignition switch since

> that

>

> >

>

> > > was a clear issue, thinking aha! gotcha this time, but nope, no

>

> > change.

>

> >

>

> > > except that now i can electric start it and the lights work somewhat

>

> >

>

> > > better.

>

> >

>

> > >

>

> >

>

> > > I've never had one that needed the battery but there's plenty of

> weird

>

> >

>

> > > differences and variations.

>

> >

>

> > Will, you your choice in bikes are about the worst I’ve ever seen!

>

> >

>

> > You must like suffering!

>

> You're uncharacteristically correct this time

>

> I run with whatever I stumble into. I've got a CR80, an Aero 125, this

> Chinese scooter and an old fanticXKE all free piles of junk and all

> slowly making their way back to functional. That fantic came from you!

> and agreeably, at least at present, is the best of the bunch. It's got a

> trac motor on it now tho - because that was also free, and because yea,

> I guess part of me does like suffering

Message DoNoHiO. He's a mechanical engineer ya know...

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