139qmb brand new carb still have acceleration issue

[br4inl3ss]

hi.
so i finally got my 139qmb running today.
its stock 50cc.
brand new Naraku racing v3 18.5 carb ( NK200.01 ).
didnt change the jet yet , waiting on the order to arrive at dealer.
so using stock 85 main jet. old carb was a 17.5 with a 84.
it fixed starting issue , but still have HUGE hesitation.
i mean... going 20 or 60 km/h , if i release the throttle and step back on it, it will hesitate for a second or 2 then its ok after untill i do it again.

float is fine
fuel is fine
valve adjusted 3 time in a week juat to be sure because everyone is stubborn on valve.
spark is fine ( brand new plug today )
even the accelerator pump is working fine.
it start right up with electric start, cold and hot.

im pretty sure its a main jet issue , but it it too rich or too lean ?
i had this problem with old carb too. its the #2 reason i bought a new one.
new carb fixed most if not all the issue but this one.

on the last ride before snow i was barely hitting 30 km/h. im back to hitting 60-62 pretty easy but i feel something while at top speed and full throttle. it feels like if the belt was slipping and try to catch up but cant. but i know its not the belt. its fuel/air related.

[br4inl3ss]

well. i guess its too rich. refuse to start today.
tomorrow wont be cold outside so ima check the plug.

[claydoh]

Adjust the needle height, probably, after tuning the carb.

The taper of the needle can effect the mixture in certain parts of the throttle travel, or the transition between the idle and main jets, iirc.

www.49ccscoot.com/faq/carbtune.html#needinfo
and
www.49ccscoot.com/faq/carbtune.html#cvneed
from
www.49ccscoot.com/faq/carbtune.html

[FrankenMech]

'Racing' carbs won't work on stock scoots without modifications to the carb and/or bike. Buy a 'stock replacement' carb for a stock 50cc scoot. You may still have to tune it to your scoot.

[br4inl3ss]

i already read those posts.
not very usefull right now. later on they will.
and i think its already at the highest point on the needle so its already at the "leanest" position , and it seems to be too rich already. ima check that when i have time.
well i think it is too rich. thasts basically what im asking.

after changing the sparkplug it started right up.
when hot i took it for a test ride, ran way better than with the old carb, but still has this damn hesitation issue.
accelerate good from a stop to top speed ( 60-61 ) but if i release throttle and twist it again, it hesitate and take 2-3 second to get back to normale.
and then refuse to start the next time its cold. spark plug already black.


EDIT
spark plug flooding right after 4-7 crank turn.
is this spark bad ? reading on the internet there is like 50 000 000 different answer.
to half people this is considered good spark , for the other half its terribly bad.

FIY , its a bit worse IRL. phone make it a bit easier to see.

[FrankenMech]

Don't be 'brainless', Buy the proper carb.

[br4inl3ss]

for info i dont see franken answer. this weirdo is blocked.
i dont need to read his false information about cdi.

[FrankenMech]

Ahh, he is blocked too.

[claydoh]

Sooooo, have you tuned the carb at all?

Maybe you need to lower the needle maybe?
You are going to have to tinker and research.

I can't tell if the spark is bad or not, seems fine but video can be misleading. Is the gap correct? It deems to be sparking off to the side a bit, though I am no expert on this.

There are plenty of threads in here with images of rich and lean plug reads.
If you are rich, you prob need to adjust the mixture (tune), and maybe drop jet sizes.

[br4inl3ss]

Mar 20, 2022 15:52:25 GMT -5 claydoh said:

Sooooo, have you tuned the carb at all?

Maybe you need to lower the needle maybe?
You are going to have to tinker and research.

I can't tell if the spark is bad or not, seems fine but video can be misleading. Is the gap correct? It deems to be sparking off to the side a bit, though I am no expert on this.

There are plenty of threads in here with images of rich and lean plug reads.
If you are rich, you prob need to adjust the mixture (tune), and maybe drop jet sizes.



thanks for the answer.
i tought needle never affected starting and idle ?
i didnt lower the needle yet. its cold outside.
but i think the clip is already at the #1 step on the niddle.
yes i find the spark to be a bit on the side. but ive seen this for years an never had any problem with such a "sided" spark.
but this is my first scooter so maybe its different....
playing with the mixture screw doesnt change anything.
i tried fully screwing it then back off 1/4 turn , 1/2 , 3/4 and so on up untill ic an remove it. i didnt see any change to this starting issue. maybe it would change at idle , but for starting , nothing change. spark plug always instantly flooded after 4-8 turn.



make me thing of bad spark plug... but damn over 4 bad brand new plug in a row ? i dont think so.>
and it started like brand new the other day with nothign but a new plug. tbh it never started that good before.
but after sitting a day and a night , its flooding when cranking and refuse to start 

can it be a bad coil ? maybe scoter coil are special and doesnt work liek any other coil... i dont know. coil usually work or dont but not half inbetween.

[br4inl3ss]

UPDATE






cleaned the carb as good as i always did.
set the needle clip to the top notch ( it was on 3rd ).
the little "jet" on the bowl near the accelerator pump was loose, could move it with finger. tightened it.
verified float level again.
adjusted idle mixture screw. from totally seated to falling off.
tried every throttle speed screw position.
tried manually playing with throttle butterfly, cable unplugged.
tried old leaking carb, no change at all.
noticed my petcock never stop fuel so i bypassed it. AGAIN. ( i have a on/off valve )

the sparkplug get wet right after 3-6 turn.
never start.
now on my 6th plug. i'm done. low on budget right now and 5$ per plug. yeah. done for now.

the spark SEEMS very weak ( im sure its even weaker than the other day ) despite what most people here said and what dealer said.
once again, i know spark on the side isnt the best. but ive never had trouble with that before on any vehicle.
neighbor damn bws run like that since 2004 and it run extremly well.

guess ill have to order a new coil and wait it for weeks only to get a definitive answer if the spark is bad or good.
thanks for the help anyhow. very apreciated. i cant ask you do to the impossible ( judging spark thru a video ? yeah... i know )

EDIT: meanwhile i tested my ignition coil. here is the result.
primary coil = 0.4k ( manual says 02-03 so i guess its still within specs ? )
secondary coil without cap = 8.40k