22 thoughts on “50cc to Big Bore 80cc Scooter Rebuild/upgrade Kit How to do it Racing Upgrades for 139qmb Engine

  1. Would this fit a pulse lightspeed 2 50cc? It's got a 139qmb engine, if not please can you recommend a 80 – 100cc kit for it as there are many variations

  2. YOURS IS BY FAR THE MOST HELPFUL ONE I'VE SEEN!  I didn't even know I had to adjust valves until I saw this.  That may explain why it's a bitch to start, sucks up fuel and lost power.

  3. Thanks to you, the engine is running a whole lot better.  I struggled with the fuel/air mixture but when it stopped backfiring and skipping, I figured it must be in the right place.  I couldn't find any specs on the spark plug gap so I put that at .03 and it seems to do okay but your vid gave me what I needed to get it running.

  4. I just got a 80cc big bore kit to put on my 50cc gy6 139QMB , the problem i got is the rocker arms are tight, i have the adjuster screw all the way out , it's as if the new values are to long , Can i use the 50cc values in the 80cc head???

  5. Chinese mopeds r pos…i just tried this and now it seems to b seized up and not even turning.. plus my kick start teeth r chewed up yet this moped is a 2010 sunny, looks close to brand new, has only 2688miles on it. Chinese crap is never good. Plus i had replaced the carb cuz they made it so u cant open it to clean the jets…its seriously a POS!!!

  6. Dude you did a good video. The only thing that annoyed me a little is the words you used for some of the things.

    The "little rod" is a wrist pin and the "nose clip" is can be called either a wrist pin retainer or a snap ring.

    Other than that it was alright.

  7. question: I ordered the 100 cc kit. it asked if I wanted the 69mm or 64mm. I went with the 64mm does this matter since most stock GY6 scooters come with a 39mm. I know all this refers to valve clearance. should I be worried about what I just purchased?

  8. i have a baotian 49.5cc scout pulse which i am fitting a 72 cc big bore to it in the next 4 weeks, then its for, sale, it is 8 weeks old done 278 miles only, new oil engine and transmission, racing variator malossi, kevlar belt and racing clutch with 2000 spring set fitted, rollers are 5 g but there are several sets to try, i am 63 years old and i am having problems with balance
    so a three wheeler trike,150cc is my way to go, a cbt for two years, and bingo, i have been told i am dying 6 months so april/may
    2017, certainly no need to take my test

  9. Check out the roller bearing cam bearings on this engine !!
    The Chinese are really starting to build some quality stuff now.

  10. can you get a more aggressive camshaft for those engines to compliment the bigger piston?
    I imagine a big bore, with a hot cam, a port job, and a bit of gearing would make that thing a pretty hot unit.

  11. my gy6 made 15,9 ps (but would have made more NM than a 2 stroke)with the 90cc naraku,malossi multivar,racing camshanft,stage 6 clutch with white springs,and the pressure spring from the vario set. 24mm naraku karb with much high fuel intake, and a Malossi open filter.A race cdi, and 2 other electrical stuff, no higher trasmission. Its a Baotian Supermoto i have

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