First Scooter Upgrade advice - Carb

[Scootz]

I got my grubby paws on 2 little 49cc Chinese scoots during Covid and we have really had a lot of fun on them. Not the highest quality for sure, but perfect for tooling around town on a summer afternoon. Between these forums and Youtube I have learned just enough to do some basic maintenance as well. I was looking to upgrade the carbs from stock to something with a bit more zing and adjustability. Can any of you fine folks give me some advice as to what would be a good choice?  Reliable vendors? Are the $30 carbs on Amazon acceptable? Can you move up from a 18mm to a 19mm without crap exploding? There does not seem to be a ton of Carb 101 for beginners out there, so any direction or advice from this forum would be appreciated.

thanks!

[90GTVert]

The main reason for a carb swap with a stock or near stock engine is for adjustability. If your current carb has a non-adjustable needle, it's often easier to swap the whole carb out than to try to find the correct needle. Screws that restrict access to the bowl or plugs over the mix screw can be defeated, but you can't always get the tune that you want if you can't easily change the needle settings.

You shouldn't really see a difference in power by moving to a 19-20mm carb. Maybe if you plan a big bore kit.

PartsForScooters is a pretty well trusted source and ScooterTuning.Ca carries some carbs.

[br4inl3ss]

agreed with scootertuning. it was my main place to buy stuff.
but since 90% of time it say its in stock but its not when you order and call them to se why nothing ship out, they say sorry its not in stock then you get a refund notification the same day. i moved away from them. thats sad because they are fucking AMAZING.

so now i go with yamaha dealership nearby, they get most of thier shit ( not yamaha/kawasaki brand parts ) from Importation Thibault, which is where scootertuning source most of thier shit, but they have it in stock for most parts unlike scootertuning and its a 1 day delivery. i dont know why scootertuning can get their stock level right and have to wait WEEKS to MONTHS to get their parts.... they come from the same place. or maybe they're just too lazy to order lol.
i ordered 81cc ncy bbk on their site, next day got a refund saying its not in stock. caleld them and they said about a month or two to restock. went to the yamaha dealer, they ordered it and it was delivered the next day. from the same place ! ( if you ask how i know they get the parts from the same place is because sometime they dont remove the Improtation Thibault sticker. 6 item out of 10 they had the sticker )

back on the main subject... why wouldnt he see any gain with a bigger carb ? all the taotao around did and the gain was HUGE for something so easy... like literally from 50 km/h to 60 just with a bigger carb ( and proper jetting ofcourse ).
i felt the same change with my naraku racing v3 18.5 carb. maybe some model are wa too small from factory ? even tho mine was a 16.5.....

[joshk]

Hey I figure this is a good thread to post my question, as it may be helpful to others later. I put a 24mm carburetor on my 80cc bbk with a 95 main jet, and when going downhill at high rpms (stock cdi fyi) she'll intermittently make a BRRRAAAAAP sound while briefly losing power before going normal again. The only solution I've found while riding was to back off to 50%-75% throttle to avoid that symptom. Could this be valve float? Too rich of a main jet? Too large of a carburetor?

[br4inl3ss]

first, a 24mm is way too big for absolutly no reason other than bein harder to tune properly.

second, i also had a problem very similar tho your with a 81cc NCY bbk.
i asked everywhere for help... and even tho alot of people here ran this specific kit, no one was able to answer.
in my case it was way too much compression. this kit was designed to work with a lower compression head. with the only notice of " doesnt work with all oem head" but it means " doesnt work with ANY owm head ".
the scrubs at ncystore made me grind my oem head and piston top to lower the compression.
fine. tis been done in car racing since the early days.
but in this case the compression was so high that id didnt fix the issue. only made the BRRRAAAAAP happen 5 min later.
had to order a 72cc sicne this one doesnt NEED a matched head. still waiting it. so i have 81cc kit sleeping in my drawer that i cannot use for shits because heads are out of stock EVERYWHERE unless i pay twice what this specific brand/model is worth ( its worth 280 CAD, the only place its in stock sell it for 560 CAD + 75 for shipping ). fuckign retarded scalpers. and no one do anything... its gonna be fun tomorrow....

anyway. your problem is way too much compression i'm 100% sure. what you describe is exactly what mine did.
i guess it will start to happen again after 3-6 second at full throttle after you backed off to 50-70 % ?