Help! Undiagnosable bbk problem!

[clydethebandit]

About a month ago i bought a scooter used for 200$ it was a standard 50cc gy6 (139qmb) zuma clone. This is before any mods besides paint and cosmetics
I have a decent bit of experience working on scooters and quickly decided i wanted it to go a tad faster. The only problem it had was the exhaust bolts had broken off in the head.
I ordered a 100cc big bore kit from amazon and installed it myself. Everything else was stock and the scooter ran great ( and with quite a lot more power)

Unfortunately my un muffled scoot was now quite loud,and after some complaints from the neighbors i ordered a new head to so i could install a new muffler.
While i waited for that part to come i did some body work. Sort of ruckus ish. I like it

Now all my electrics are exposed and i had the displeasure of riding through a rain storm the day before my new head arrived from amazon, and for some reason, my scooter just quit on the way home. It wouldnt start at all.

Worried that i wouldn't be able to get to work i quickly ordered a new ingniton, a new air filter, a new cdi (which did not fit) and a new carb.


Everything came at once so I thought it would be good to get it all put it on. I'd have a quiet scooter and fix the electrical. Sadly things are never quite that easy. The new head I got head off the shorter valve stems and the rocker arms on my engine work at the right angle to make contact with them. With the new had tossed aside I put all the electrical on set the timing and tried to fire up my scooter


Keep in mind my scooter ran perfectly before this little rain incident. And the only Parts have switched out are an identicle ignition a new air filter to replace the homemade one and the carburetor.
Now for some reason that I can't figure out my scooter will start and idle, but whenever I go to give it any gas it Bogs and dies. I've tried raising and lowering the needle in the carburetor, I've got my valve clearance and timing perfect, I've got a brand new spark plug and I've checked if the old carburetor would work. It does the exact same thing. My petcock is fine and my gas lines are brand new and not in any way blocked. Remember this is the exact same setup that worked perfectly before anything got wet, and I've replaced everything that could be damaged by water. I just can't figure this out at all and I'm completely stumped as to why my scooter won't run at high speeds or even get past an idle for that matter. If anyone's experience this problem even with an unmodified scooter any advice would be greatly appreciated. Everything that I have done to it I've done right so I can't figure out why in the world it isnt running. HELP!

[clydethebandit]

P.s. i meant do not work about the rocker arms, and the scooter sounds like it bogs when i rev it, but it I've leaned the mixture as much as I possibly can, and it makes little to no difference on my performance at all

[clydethebandit]

vimeo.com/166728841

[niz76]

Welcome Clyde!

Great job on giving us lots of info and pics to work from- nicely done sir. 

With all the info you've provided, I'm inclined to think that maybe your air filter is at the root of these issues? Changing air filters alters the ratio of incoming air to fuel so the carb needs to be jetted properly for the new change. Needle height changes affect mostly mid-range power so you'll need to find the correct main jet first.

Is the replacement carb the same size as the old one?

Is your old air filter still useable?

The proper way to solve the issue would be to get a selection of main jets and tune the carb and find the right one for your air filter, however if you'd like to get a little "ghetto" you could wrap some tape around your air filter to restrict it and see if you can find the right balance of air/fuel.

These are just a few quick suggestions to get the ball rolling. You're in the right place to get your baby back screaming again!

[clydethebandit]

Thanks for the reply. My old air filter wasn't really much of a filter at all, it was just the connection from where the filter used to be with the screen in front of. My scooter had been fine with that before, and I was worried about my Jets clogging which is why I went out and bought a real filter. I have tried restricting the new one Kama as well as completely removing it end of covering the opening for air almost completely with my hand, and it makes no difference. It is possible that the issue has to do with jetting , but as I mentioned a scooter in perfectly fine with the Jets it had before I rode through a storm. That's part of the reason I've had so much trouble figuring this out is there so many problems that I've already ruled out...

[clydethebandit]

Replacement carb is also the same size and style, and I have the same issue with both the Old and the new one.

[clydethebandit]

If you look at the video I posted it basically does what it's doing in that video regardless of anything I've done to the air filter or which carburetor I use and how i tune it, How perfectly I set the timing or which igniton or plug i use. Im so stumped

[2stroked]

Hold on, You had the displeasure of riding it in the rain.....with no exhaust attached..


I am not sure, but is it possible that water could have splashed in to the e,haust port? If it could have and did, it may have destroyed the valve guide and seal, causing a loss of compression.

[clydethebandit]

No I took the cylinder all apart to make sure my rings were spaced properly just this afternoon and everything is perfectly fine in there. There is no water or signs of there ever being any. I actually put the new head that I bought back all in the end I got my rocker arms to align right did the timing in valve clearances again but it's still having the problem.
I tried putting a more restrictive air filter on it and it actually did help a little , but it's still far from rideable. Does anyone know where I can find jet kit for a GY6? It's got a 100 cc Big Bore Kit on it but it technically is more like an 80 just advertised as a 100cc...

[clydethebandit]

Also the head I put on it came with valves so even if the old ones were damaged it has new ones on it now

[niz76]

Many of us order from here and I've never heard any complaints. I love this place!
Usually a uni or free flow filter requires a substantial upjet so you might even need a few larger than what this kit supplies...

www.partsforscooters.com/114-49-QMB139-Main-Jet-Kit

[sumo210]

May 15, 2016 19:30:48 GMT -5 clydethebandit said:

Also the head I put on it came with valves so even if the old ones were damaged it has new ones on it now

Ok as u said it came with this, my questions to u is what kinda of head did u have a 64mm or a 69mm, there is a differnce, the reason i ask is because the head ur using"the new one" is most likely a 64mm and the stock one is probably a 69mm. or vice versa, and those rocker arms they sent may be the one u need to change in order to work with the new head. if this is so the stock rocker arms and the new ones will be different, slighty but different. the 69mm will be more straight and the 64mm rocker arms will have more of a curve, make sure u look at this because it can be the differenece between a good working motor or a complete screwed one. i did the same thing to my taotao and ran into that issue i couldnt figure it out for over 2 weeks but as soon as i changed them it started right up.

[sumo210]

Also i agree niz76 i had the same set up as u do on mine and i had to upjet, it seems to me that if it idles then dies when u turn the throttle u might not e getting enough gas. order a set and try them, make sure u order the right ones though i had the unfortunate luck of getting the wrong ones and they wouldnt fit my carb, so i just drilled mine out by hand i wouldnt recommend that but its just temporary for now. may help u get it running until u get the real ones..

[Silar]

Check the fuel petcock. It's vacuum operated and does (or will) fail and can cause gas to go straight through the vacuum tube and straight into the intake. Not saying that's what is causing your issue, but it could be. Just replace it with a manual petcock from Advance Auto parts or other auto parts place.

And on the other side of things...
Also check your vacuum tubing and make sure you're not overly lean. Check for cracks in the tubing, and/or disconnected tubing.

and..
Check your spark plug. Make sure you're getting good spark. Also make sure your spark plug isn't cross-threaded. I ruined a head by putting the spark plug in wrong.

[Fox]

You may already know this but running without the fan shrouds and fan cover is not advised. They direct the air from the fan around the cylinder and head to cool it off. No shrouds = overheat.

Get an NGK plug cap and screw it onto your plug wire. It will seal out water better than that stock style cap you have now.

4 for $12 shipped is a great deal:

www.ebay.com/itm/NGK-SPARK-PLUG-RESISTOR-CAPS-SET-OF-4-/222121237835?hash=item33b7751d4b:g:4-sAAOSwt7pXMiH8&vxp=mtr