KR-1S.co.uk Forum

Right my KR1S carbies are on an LC but please bare with me on this
From my first time on the bike after the build,i had slow running troubles on the carbs with poor tickover and bogging off the line etc.
Always been fine over 4000 revs and pulled a healthy 59.9 on the dyno
I messed about with this most of last summer and finally solved it by fitting bigger pilot jets (#45).
I have ridden it for ages now and all was fine but the original problem has reared it's ugly head again .
I cleaned the carbs several times including the jets and it still wasn't right,i convinced myself it was a blocked pilot jet and got some new ones expecting to have cured it....it didn't
So i'm at a total loss to what it could be
I have messed about with the airscew and it has no reaction whatsoever.
I have totally stripped the carbs including the bit where you take the security screws out to get at the tiny holes there.
Spent all afternoon f##king about and yes i am f##ked off

PLEASE,PLEASE HELP

just a thought but have you tried changing the plugs?

sometimes they can affect tickover/slow running if they are on the way out

I have changed the plugs (no difference) and i have ordered some dynatek mini coils as i guess this coil is at least 25 years old plus the HT leads are fixed into the coil body so you can't change them which i have never liked .

Had another play today and put in some spare PWK's on the LC but as it was pissing down i didn't get a chance to take it out.
I could be on the case though
It was pulling away at ultralow throttle on the drive though but the tickover was poor,it may just have needed a blast up the road to clear it a bit as i'm running premix.

I think now there is a blockage in the bit you detach from the body that is held in by the security screws.
I have ultrsonically cleaned them a few times but i think there is someting stubborn in there that doesn't want to come out

i've had a problem with poor starting / running on one of my cylinders

cleaned the carbs out loads of times plus removed the piece you are referring to - poked bristles from paint brushes down those fine holes - still no luck

was just about to give up and decided to swap pilot jets between carbs -
problem changed to the other cylinder

just got a new pair of pilots and fingers crossed this is going to solve the problem

i think problem is pilot jets look clear, but they aren't, and i don't think you
can really get them clear - perhaps yours are slightly blocked (even the new ones) - do you use in line petrol filters?

Hello Gazza
i did change the pilots and like you say they can look clean but there is something still in there.
Like i said above this didn't cure the problem.
I had an old tootbrush and was poking all the holes out with a strand off the brush.
I have just fitted inline filters too.
Just waiting for a break in the weather now,blummin typical

Have now fitted KX 85 carbs as i had these for a while but not fitted them.
Put in the JJH needles off the other carbs and a new pilot jet which is a #45,the main jets are the big hexagon types on here and put in a #150 main same as the other jets i have been using.
It is now nearly there and just need a play with the airscrew but found that if i put in a smaller pilot (#42)jet,if i roll off the throttle it would baulk and hunt and the engine wasn't happy at all
The only thing i'm worried about are the KX 85 carbs which are PWK 28's,are they the same internally ?

I have tried to describe the symptons a bit better here.
See what yer think ???


My hybrid LC with 350 YPVS engine has a few carb issues.
I was running with PWK 28 carbs off a KR1S 250 bike for ages and now they have some sort of blockage so time was to fit my new shiny KX 85 carbs which are PWK 28 carbs too.

Spec is

YPVS 350 engine
Mick Abbey fast road tune
V force 3 reeds
Allspeeds with detachable end cans
Ramair filters (like uni pods)
KX 85 carbs(PWK 28's)

jetting
#150 main jets
JJH needle clip #5 (richest)
Pilot jet #45
Airscrew 1.5 turns out.

It feels really strong in the powerband but it's part throttle that seems to be the problem
If i roll off the throttle from the powerband and it drops sub 4000,the engine jerks and lurches and you can actually hear it whip the chain,not happy at all.
If you only rev it to 4,5,6000 revs then drop the throttle ,this jerking doesn't happen.
I cured this with the old KR1S carbs by going up on the pilot to a #45 but the KX carbs already have the #45 fitted !!
If i turn the airscrew in from 1.5 to 1.25 or 1.00 turns out then at about 3000 revs at part throttle it sounds like a machine gun !!! then smoothes out at 4000,it has a real sweet spot at 4000.

Because i have the pull up type chokes on these carbs,from cold it will surge to 4000 revs and i have to quickly knock them off which stalls the engine.
I get over this by leaving just one choke on which lowers the revs to about 2000.
Also once warm the tickover sits high at 1500 revs.
All the other crap ain't too bad but it's the bloody surging that is really annoying me.

Question is shall i go bigger on the pilots again or am i barking up the wrong tree ??.

.
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as said in previous posts..
DO check your throttle cable routing around the headstock,
and ensure there is a good couple of mm freeplay on the twist before ANY slide action. There should be no change in idle at standstill when you turn the bars lock to lock.
You wouldnt run your clutch cable with no freeplay (it be too tight and enough to slip once warm) - why do it on the throttle?

If the idle is high you need to richen it so it falls readily to below 1000.
When the airscrew is adjusted to its limits change the pilot jet.

My KX125 when started cold on the choke would rev its nuts off - but I just used to immediatley kill it once it had started - then the second time it would be much happier to stay lower. When warm it was a toss up to have your idle quite high or have it not idle and die on no throttle. On a ride bike you want it to be civilised and behaved when you pull up at the lights.

The cable doesn't cause any pulling of the throttle slides when i turn it from side to side.
I'm really tempted to try a bigger pilot jet,next one is #48 then #50 just to eliminate that theory.
I do have a local dyno shop just down the road and maybe let him have a look at part throttle openings ?

http://www.sudco.com/CatalogJPG/069.jpg

the little chart it top right corner of above image...
the JJH needle designation the H is for needle diameter and effects the zero to 1/8th to quarter region
you could go richer on small opening on needle (instead of slow/pilot) by going smaller needle diameter 2.435mm (H) ... 2.425mm (G)... 2.415mm (F) depends on whats readily available at your local

Jets are resonably cheap so you should try a pair of much fatter ones (take a bigger jump on slow/pilots to try and notice difference)

on my YZF (FCR's) my local messed around for ages on drilling slows/pilots to get good roll on response and in the end all it needed was clip needle - the problem here was we didnt identify the larger opening and therefore clip/needle not slow running - IT PAYS to know the carb and what components governs what at particular throttle opening SLOW/AIRscrew >>> NEEDLE >>> MAIN

the KX125 (35's) was a bit more tuned than the KR-1R (35's) so the stock carbs are much richer in slow and main.
Similarly your 350 (175cc x2) would require a heap more fuel than the 85cc or KR does

Been advised to drop the needle to middle position and go down on the pilots to something like a #40
I will try this but you never know

Spooky. I have the same engine spec and the same symptoms on my hybrid, pulls like a loco above 4k, bogs on tickover etc. I have some pilots on order [various sizes] ,when they turn up i will have a play.
Im currently running #39 pilots so going down to #40 may not be the way to go

Ok, jets arrived, stripped the carbs off, clean as a whistle inside, including the pilots so dived in with #65 pilots to start with. All back together, fuel, chokes on, fired second kick ticks over on choke @2000rpm.
Knocked chokes off and it settles to around 1200rpm, i need to do the following next
Adjust tick over screws for slides.
Drain the tank as the premix is way out [cough :-& ] and top up with clean fuel and A747
Book some dyno time

Hello Nick
I went for #48 pilots in the end and it cured it again.
Another thing with the JJH needles it would NOT run with anything less than clip #5 (richest)
As i have the KX 85 PWK's fitted now i also went up one size on the mains so now running #152 mains.

Also just fitted a dynatek coil and only had it running on the drive but tickover from cold has greatly improved so fingers crossed i will give it a razz tomorrow

Aup Martin
Mid to full throttle is good on mine with 130mains and needles 'as they came' but i will look at that at a later date, no time now til next week.
If you do owt else to it in the mean time, let us know chap