Gilera stalker 70cc kit bogging (need help tuning my carb)

Hey guys i'm very new to scooter tuning, i have this gilerka stalker, swaped a 70cc kit on it because the stock engine siezed. And i can't get it to run properly.

A couple of months back i bought this pwk chinese carb, and some main jets i think 80-125, and slow jets 25-50.

I tried a couple of combinations:
1. 40 slowjet, 80 main, a/f screw 1 1/2 turns out
2. 40 slowjet, 95 main, a/f screw 2 1/4 turns out
And some other combos i forgot, and it never really ran great, right now im running 40 slowjet, 88 main, a/f screw 1/2 turns out and the needle clip one position leaner, seems to run pretty good on the low end (when the bike is on the stand it revs out really good and seems to sound the best it ever did, even if i twist the throttle all the way), but as soon as i open the throttle all the way it bogs and sometimes it runs better with the choke engaged, im thinking its too lean of a main jet, but im not sure, as i said, im pretty new to all this carb tuning, watched a couple of tuning guides and read some forums for tuning but i stilk cant get it to run right.

Forgot to mention, the whole scooter is stock, except replaced the cylinder and piston, and im running a mix of 3×4 and 3×8 gram rollers

Note: im also running a stock exhaust maybe this could be my problem? (i know its recomended to switch the exhaust when installing a 70 kit, i just dont have the money to buy an exhaust rn)

Note 2: just swaped a new plug in yesterday, i rode it around my city a couple of minutes (like 10 or so), and yesterday for about the same amount of time, the sparkplug seems to be the same color i unboxed, no discoloration

 

The chinese pwk style carbs can be a bit hit or miss for quality, and is more than likely ott on a std (ish) engine anyway.
you are much better buying A Dellorto PHBG style carb, A sport 70cc cylinder will run pretty fine on a std carb, even if its only 12mm (ive done it)

I would need more information about the parts you have fitted, before i could begin to help.

what size is the carb ? what 70cc kit have you fitted ? what exhaust have you fitted ?

 

Hmm, i bought the carb off a friend who has some experience with tuning scooters, it was fitted as a replacement for a stock carb on a 4 stroke chinese scooter, after he bought a 90 kit for it, and it ran great on that scooter, i still have the stock delorto PHVA 17,5mm, but some people kept saying i need to buy a bigger carb like a 21mm or so. the kit that i have installed is a naraku racing kit, i will try to find more info about it (it came with only a replacement cylinder and piston, as i said i only bought the 70cc kit because the price of this 70 kit was almost the same as a stock cylinder and piston)

the exhaust is stock for a 50cc engine, but im planning to buy something with more flow if thats the issiue

Edit: the carb size is 21mm, and the jets im curently using are 38slowjet and 88 main with the a/f screw 2/3 turns out

 

I am not familiar with a Naraku 'Racing' 70cc cylinder kit, and a Google search has turned up nothing.

However, you may have a Naraku 'sport' 70cc cylinder kit https://www.pedparts.co.uk/product/2794/naraku-70cc-cylinder-kit-piaggio-50cc-ac

if that is the case, then a PWK carb is definitley a bit o.t.t, as its described as a low revving sport cylinder which provides a small increase in
power over a stock cylinder.

The good news is, it will work fine with your stock exhaust and your Dellorto 17.5mm carb.

You could also fit a budget sport pipe too if you require a little more.

refit the 17.5mm carb and go from there...

 

That seems to be the same one i have, i will try to refit the stock carb and buy bigger jets, and let you know how it goes, thanks for all the help tho

 

dont go too mad on upjetting for that 70cc cylinder, it probably only needs the main jet increasing a little, especially with a standard pipe.

2 or 3 sizes up from the std jet will be fine, keep an eye on your plug colour, you are looking to achieve a tan colour on the centre electrode porcelain.

 

Update: i replaced the carb back to the stock one, i upjeted the main jet as suggested on the kit desc. (went from 65 to 78) and i have the a/f screw 1 turn out and it still bogs at full throttle, i will try to post a video so you can hear it. tried turning the screw either way, if i turn it out more it bogs, if i turn it in more it seems to run very rich (judging by exhaust smoke and occasionally sputters). i cleaned the carb before installing

i checked the spark plug seems to be normal brown/white in the centre. cant seem to figure this one out, could it be that my rollers are to heavy so the bike bogs? could be that my fuel supply is limited and it bogs at wot?

 

Here is the video i took, i hope it helps to diagnose my problem. https://we.tl/t-4RkX6Aud26

 

Im afraid that link doesnt work for me, it just takes me to a hosting site that then tells me to log in.

I had another thought: what type of air filter are you using ?

 

Im using something like this: https://www.aliexpress.com/item/400...xp_id=57250f88-6c8e-4432-91a8-c8e87a8f603b-11. but i tried to remove the filter and it made no difference, i will swap back the 21mm carb because it ran better, and ill try to tune that a bit, but i guess this bike is just cursed or something

 

An open filter like that one will make a massive difference to the main jet needed.

 

as i said, i already had a 88main and a 40 pilot, i put the bike back together today with the 21mm carb and i got it to run somewhat okay, but thanks for all the tips anyways, will post here if i have any more problems over the next week.

 

I think i know what was my problem with the 21mm carb, but i have no idea why the stock carb didnt work. The 21mm carb has one slight problem, the pilot jet keeps unscrewing, i took apart the carb today, and found it at the bottom of the bowl, put it back together and it started to run great, guess ill be tightening the pilot jet every so often, or buying a new more suited carb

 

Brass into aluminium, shouldn't un-screw itself.........

 

welp i dont know what to say to you man, as i said i found it at the bottom of my bowl, and im 10000% sure i screwed it in all the way. and this is the second time it came undone. maybe its just a damaged thread or something but i cant see the damage, and i really doubt that the pilot jet socket on the carb is aluminium, its probably a mix of chinese metal tho.

 

glad you got to the bottom of your running issues

 

welp, im not sure if i should open another thread for this but, my bike developed a new problem, seems to not run when warm, i looked all around forums and stuff like that, everyone is saying that it could be running rich, i doubt it, no or very little exhaust smoke when started and running (im sure its getting enough oil because i premix it, im using a 2% mix for anyone wondering). basically my problem is that the bike bogs when it gets to operating temp., i start it, let it sit for about a minute idling go for a ride, it bogs straight away, if i drive it cold, (start the bike and get to riding as soon as it starts), i can ride it for about a minute or 2, then it bogs, i stop sitting there at idle for about 15-20s twist the throttle and the bike responds as it should, ride for about 30s and the story repeats, it wont move under its own power for 15-20s i sit there idling, twist the throttle and the bike shoots off. i can see why people think its just a rich tune, because that's the most logical thing, but i still have a 80 pilot and the a/f screw out 2 1/2 turns, im just really confused about this bike, never heard anyone had the same problem as me, and none of my mechanic friends seem to figure this one out. (i saw one guy said it was a stator but idk how to troubleshoot those and wouldn't the bike not start if it were the stator?)