Big Bore Upgrade Aftermath 39mm to 50mm

[40329253]

Dear all,

Please see me as humbled and stupid user.

Fall in to advertisement and think average(Friend's friend that claimed he can do it blind) service can do the necessary upgrades...

I had a GY6 139QMB 50cc(39mm) scooter that with my friend saying can be improved.

With his lead i purchased a big bore kit (50mm big bore kit) that only comes with piston and bore of it.

After installing it (because he try to put fault on another parts like coils or stators without thinking that this scooter goes in the shop without a problem) there was a problem i just took my scooter and left because he fckd it all up.  

Explanation of my issue at this moment; 

Scooter idle without an issue,

Originally think this engine can 7.500rpm max 

Now it can only goes up to 1.500-2.000rpm 

If you try to go up more rpm it bogs down.

If try to squize till the end it goes up and down like trying to goes up the rpm and crash down.

Please help me... This scooter my everything that my hand and legs. Also only vehicle for me to go to my work and back...


I'm desperately need your help... 

[aeroxbud]

Welcome to the forum.
Does your scooter rev up on the centre stand. Can you post a video of it riding?

[scooter7878]

A video would help but I would guess either some kind of timing or valve train issue cam timing off,or something with the valve adjustment or rocker assembly,maby a ring issue leading to low compression first thing I'd do is check compression/cam timing and valve adjustment. I imagine it should rev more than 2000 rpm even it it wasent up jetted. Maby possible intake leak or carb way out of wack but compression and timing is first thing I'd be checking

[GrumpyUnk]

If you feel capable, it might be a good idea to check the cam timing and valve adjustment. Then check that the fuel petcock is allowing fuel to flow through the filter to the float bowl on the bottom of the carburetor. The intake vacuum opens the valve, or you can apply suction to the line from the intake to the petcock and that should open the valve and allow fuel to flow. Fuel should flow as fast as it can come out of the fuel line, full diameter, with no pause or dribble. Any other flow indicates a stoppage or blockage, such as the tank outlet filter screen, the filter, or the fuel lines.
I would make sure the carburetor is installed fully to the intake manifold with no leaks, and that the manifold is tight on the cylinder head.
If your 'assistant' did not put the air shrouds back on the engine, you must do so, or the engine will overheat and the piston/rings/cylinder get ruined.
Working on the piston/cylinder does not require messing with the CVT, and if it worked well before, it should continue to do so without intervention.
tom

[madlymad]

Dear caring friends,

After a national holiday an another (proper) repair shop checked the scooter, left it there for two days.
They fixed the problem which they said timing was slightly off and that was causing the issue...

Now finally i got back my baby and really happy to have her back.

Now i need another expertise of yours...

When my ignition is on, my lights doesn't work, engine has to run for my headlights to work which when idle it is pretty dim and goes bright as long as rpm is high. Which also causing my bulb constantly blows every couple of months...

Is there any way for my headlights runs over my battery rather than stator?

I am so thankful for your care!! And much appreciated!!

Kind Regards..

[claydoh]

I think this headlight wiring setup is common, and normal. The bulbs probably draw too much power to be run off the battery directly, the stator can't charge the battery fast enough to power the bulbs for very long (or the battery can't take a charge fast enough to be useful for headlights)

The dimming is normal as well, especially noticeable if the idle is too low, but every qmb139 scooter I have had has done this. You could swap to LED bulbs, which could be re-wired to run off the battery. Those might not use much current, and not drain the battery so much.

Blowing bulbs can be from poor quality parts, getting oils or grease from fingers on them (maybe?), a bad regulator/rectifier, or bad wiring.

[GrumpyUnk]

The variation will occur unless you run the bulb off DC voltage from the battery. There are mostly two charging windings, one is rectified and regulated, and provides current to keep the battery charged, and run the cluster widgets. The other is not regulated(well, not to battery voltage) and is used to operate the headlight. If the regulator is cooked, it may allow a too-high voltage which will either 1)burn out the filament, or 2)shorten the filament life. You may want to put a meter on the un-regulated side to see what voltage is being fed to the bulb.
If you want to get fancy, you could link the two outputs, and rectify/regulate the whole thing, and run the bulb from that regulated DC voltage. Not too sure if the battery would stay charged without help.
Other bulbs such as halogen and LED may work better. If you go LED be aware that the light may be bright, but if it is not reflected or concentrated such that its output hits the internal reflector(shiny curvy part) improperly, you will have a very diffuse light produced that may be worse than others. That happens a lot in LED headlights on cars and trucks. The reflector is designed for a 'point source' light to reflect properly.
tom

[steve1297]

These scoots blow bulbs because of how they are wired. It's a design flaw. The best thing to do is to get some LED lights and run them off the battery