pwk 28 (keihin)

[qwerty123]

hi guys
im having trouble trying to get my bike to run. it idles (not very well) on richest needle setting but when i tap the throttle it revs up and stays revving even though i released the throttle for about 2 and a half seconds then drops and almost stalls itself.

my build
ported big valve head
a2 cam
hd valve springs
57x57 bore stroke (146cc)
high comp piston
and the carby is a keihin copy pwk 28

and any other needle setting really doesnt work at all only the richest idles
idle mix screw seems to work best when its all the way in



any tips to get it running right?

 

[sean01]

ok you havent told us what needle its running or the pilot and mainjet

 

[qwerty123]

pilot 35
main 130
needle unmarked

 

[sean01]

ok well to start with your jetting is way off...and im guessing this is an akunar carb if so was it one from the top of his list?
and does it run hex mainjets?

ok, leave the needle in middle position for now
you need a 96/97 mainjet
i would get a 42/45/48 pilot
try it with the 45 pilot first and see how many turns out the mixture screw is

chinaboy just tried a 45 in his and it was about 2 turns out so he's gona try a 42 and should make it pretty spot on..

 

[qwerty123]

yes it does run hex main jets and yes it probibaly is from akunar.
thanks for the advice

130 to 97 that's a big drop and it runs worse when i lean it out why would you reccomend smaller jets?

 

[sean01]

because 130 mainjet in a 146cc engine is just plain crazy, its a 2 stroke carb hence the reason they come with such big jets

have a look in the carby thread where everyone posts up there carb settings

and leaning the needle out isnt the same effect as leaning the main out

for the record my yx150 with 28pwk copy runs a 50 pilot and from memory a 98 or 102 main

now for starters your pilot is a mile off it will be running super rich at idle and the mixture screw will have no effect at all no matter where you turn it, bounce a 45 pilot in it and see what happens

 

[qwerty123]

oh ok

my idle is super rich don't you mean super lean. bumping 30 to 45 makes it richer right?

oh and do keihin jets work in my carb or do they use a different setup?

 

[sean01]

higher number on the pilot makes it leaner because your adding more air to the pilot
they work the opposite to a 4 stroke carb

keihin hex jets are fine, you can get jet kits from DHZ

 

[DvDRip]

higher number on the pilot makes it leaner because your adding more air to the pilot
they work the opposite to a 4 stroke carb

hmmm, never knew that does this apply to oko's?

 

[china boy788]

did you block off the air port behide the choke? got ur power jet connectored up?

if its the top on off akunar, well there ment to be real keihin pwk, btw, there just pushed out the back door,

 

[sean01]

hmmm, never knew that does this apply to oko's?

yeah dvd all keihin 2 stroke carbs

 

[qwerty123]

yeh i did block off the air port. what is that thing supposed to be for?

and power jet i don't know what you are talking about

the carb where its supposed tosay keihin it is grinded back and has a s curve to it
also has a polished slide.

and a hex nut bowl

looks exactly the same as the one on top of akunars list

 

[china boy788]

hmm, ill post wat one mines looks like and where the ports are and the power jet,

i can c kehin clear as day.

jst cant c it cuz of the way the lights on it, but theres the power jet

top should be blocked

not best pic but shows how to block it easy

 

[qwerty123]

by power jet you mean the tube that runs from the bowl to the top of the inlet what setting shouldit be on?

and my carb seems to have a darker more greyish cast to it, yours is so shiny
and mine has no print saying keihin
other than that its the same

 

[china boy788]

yer and with power jet, woodnt know, it jst runs beter at high revs, ask thump

whered u get urs from?

 

[qwerty123]

got mine from a guy that used to run a shop called fusedminis and that was a few years back.
cost me 60 bucks with the rubber boot

 

[china boy788]

checked for a air leak then?

have a read of this
http://scootrs.com/tech.cfm?tip=tunecarb#e

from the top,

 

[sean01]

ok DVD you got me worried lol, so i checked and rechecked most of the tuning guides tht i go off..

now it does seem tht wat i actually said was backwards but my point is still the same..
to correct myself larger number on the pilot richens the circuit..

having corrected tht everything else i have said still stands...
your pilot is too small hence the reason it doesnt drop its revs and idles like sht..

as china has said, have a read of this http://scootrs.com/tech.cfm?tip=tunecarb
its really confusing to explain because you end up doin the opposite to what ya think to tune the pilot

 

[Cactus Jack]

The FIRST thing you should do before tuning a carb is double check the cam timing and valve clearances to make sure they're set right and that the valves are sealing properly ... An inlet valve leak will make carb tuning inconsistent and make you think the carb is faulty ...

The pilot jet size controls the peak volume of fuel flow from the float bowl ... so bigger is richer ...

When the mixture screw is on the air filter side of a carb it's obviously an air screw ... and it simply controls how much air is added to lean out the mixture ... When it's screwed right in it cuts off the air flow and allows raw fuel to be sucked up from the float bowl ... as it is screwed out , it allows air to mix with the fuel which lowers the volume of fuel being sucked up from the float bowl ...

4 stroke carbs have the mixture screw at the rear ... so it's a fuel screw which acts like an adjustable tap valve and simply controls the volume of fuel that's allowed to flow from the pilot jet ...

The pilot jet controls the volume of fuel that's allowed to flow up from the float bowl ... The fuel screw simply allows the pilot jet flow to be fine tuned ... screwing it right in cuts off the fuel flow ... and screwing it out increases the flow which is ultimately limited by the pilot jet size ... The slide lift which is controlled by the idle screw , controls the idle air flow ...

Qwerty's pilot is probably too lean that's why he has to have it screwed right in ... and since his pilot is too lean , he has had to go big on the main jet to get the engine to run OK ...

As Sean says ... the first things to fix are the main jet and the pilot jet sizes ... You've got to tune the main jet size in (with the needle clip on the middle groove) ... until the engine will rev out crisply and cleanly up top without detonating , bogging or spluttering ...

With a cam , the vacuum is poorer at idle so the pilot usually needs to be richer ... but at higher revs the vacuum will be stronger due to greater cylinder filling so the main jet will need to be a lot smaller than #130 ...

Thump*140's flatslide carb threads are full of useful and usable info ... and he's tried a 28 OKO on a 140 ... The jet sizes he's ended up running should be a good starting point for you Querty ...

 

[qwerty123]

ok thanks
well because hes using 95# main on a 140
i could go 100#
and a 40# pilot

why is thump 140 using a 36# pilot or is there a difference in oko and keihin jets??
my stock pilot is 35# wtf???

seeing as i have 146cc and a ported head

in theory would this be more suited to a slightly larger engine