keihin PD idle

[Hyzer]

Hey got this link 250 going again.

works great, BUT it will only idle off choke (when its warmed up of course) with the idle speed screw all the way in.

just pulled the carb down cleaned it out 100% and put it back together and it didnt change, so ive replaced the o rings and gasket on the manifold and just did the valves (.05mm intake .08mm exhaust) + oil change. it starts easier but it still doesnt idle at the correct speed. it was doing this when i got it originally btw.

the fuel adjustment screw seemingly does nothing.

its a Keihin PD with a 24mm slide - probably a knock off i guess - with the following settings

main jet - 88
idle jet - 34
the float is level with the base of the carb, not sure if thats correct but it seems so. theres not much info on these carbs!

running on 98 octane fuel

it also runs great off choke through all the gears but it just wont idle without the choke or a bit of throttle held on.

if you need anymore info let me know! hoping to get it going for the weekend for a bit of fun.

thanks

 

[sean01]

ok, for starters you valve clearances are wrong....probly should be set at .005 tho and .008 tho which is in inches you have done metric

are they the standard jets that come in the carb? and is this the original carb?
is it possible to try another carb?

will it idle with the mixture screw about 5 turns out or more...

sometimes carbs can act up and theres absolutely nothing that can be done because they have been poorly manufactured....meaning...good one day then bad everyday after

also how is the air filter? try tuning it without it on if your in a dust free area to see if it makes a difference but dont ride the bike around the yard or anything..

 

[thump*140]

^^^ pretty much what i was going to suggest. If that doesnt work, set the original carby on fire, buy an OKO 26mm, and be done with your woes...

PS: The OKO26mm rips on the 250 upright motors.. even more so than the horizontals.

 

[sean01]

lol yeah i use to have a bucket full of china Keihin carbs that just didnt want to play the game anymore

 

[Hyzer]

aright ill check it out, i tried it without the filter and no difference at all.

as for valve clearances i couldnt find anything on the verticals - so i followed this recommendation - its the same motor as ive got but with the air injection port.

YouTube - Chinese motorbike adjust valve clearance 1

but if its definitely in thou ill go change it.

not sure if there the stock jets it came with either, just what i recieved with it. id imagine they are though as nothing else on the bike looks like it was ever touched

i think you might be on to something with the fire anyway

 

[thump*140]

same here. I have a theory that the choke ports are responsible, as they show no apparent reason for failing, and yet they all exhibit the same symptom... ie: die in the ass when you crack the throttle. if they do keep running, they lean as buggery and shoot awesome footlong flames out the back. used to light my smoke with the Thumpstar that way. heh heh.
Now i smoko OKO's.

 

[Hyzer]

hmmmm doing some more looking around it looks like the clearance is .05 and .08mm pretty well everything i can find says thats about what it is. not so sure what the correct value is now

ChinaRiders.net - Your online China Bike community Forums-viewtopic-Valve Adjustment Tutorial
QM200GY idle problem, valve clearances. - MyChinaMoto

might be a good excuse to get that OKO

ive got a tiny 16mm carb off my mid bike but i dont think it would even run with that on there haha. might be worth a go?

 

[sean01]

to give you an idea .05mm is .002 thou. now once the engine heats up the valve train will more than likely expand about .003 thou...hmmm wat does that mean...the valve is held open

set the rockers @ IN 0.10-EX 0.15mm as sated in the last link you posted... so that is approx .004 thou on inlet and .006 on exhaust...

no engine can run with such tight clearances

 

[Hyzer]

no problemo, doin it now. see how it runs tommorow. thanks dude

 

[Hyzer]

problem is SOLVED. the valve clearance was the problem thank you sean!

runs with the idle speed screw about half out. sounds heaps cleaner as well. time for some fun.

 

[sean01]

too easy...good to see you got it all happenin again

 

[Hyzer]

sorry to dredge up this thread again, bikes working good, but it surges badly coming off throttle. if you roll it on it slowly it will rev out to full speed fine.

do you turn the fuel screw in for lean and out for rich? i cant remember for the fuel screws (the one on the inlet side of the manifold). the plug is black as the ace of spades so its hugely rich. i think its in for lean so its 3/4 turns out from fully in and still running mega rich. which is a bit of a worry. so hoping ive just got it the wrong way around!

could any other problem with the engine cause this aside from jetting either? i did the clearances as described earlier and its got a new NGK plug, brand new coil and new oil. just curious in case i end up chasing my own tail trying to find the problem

thanks

 

[sean01]

well ideal mixture screw setting is between 1 1/2 and 2 turns out from closed(fully screwed in)
screw it in for lean..

also where abouts is your needle clip set at? sounds like the clip needs to be raised a notch (raise the clip drops the needle)

 

[Hyzer]

cheers, needle is in the center position so ill give that a go.