the carby situation,guidelines needed...

[aussiemonster]

hi guys ,just back from the bush(it was really hot as always,fried my feet and my brain,again as usual!),anyway back in perth,got my 26 oko carb,manifold ,air cleaner,throttle etc from dhz for 89 dollars.
i opened the carb first to take note of the jet sizes.main 102,pilot 39.
set the whole thing up on the bike.had to raise the tank 4 mm (this is on an rx 125 motovert),as the carb top was interfering with the fuel tap.
the bike started first hit of the button,and low speed stuff was good.
but once i open the bike up it is like i have hit the kill switch.when i bought the bike it ran out to top revs good with the original carb (26 but really 22 mm mikuni),once i put the big bore 146 kit in and lifan head etc it did the same thing,until i took off the shitty air cleaner off,so the symptoms are identical ,so i figure it is not getting the air it needs,so with the new oko i took the air cleaner off and that helped a bit so i figure it isnt getting enough air.any suggestions,i understand basic carb set up but dont have the depth of knowledge of cactus or mack,just wouldnt mind a push in the right direction.if it all gets to hard i will take it to a shop,anyone have any one they recommend here in perth,any guru's over here.with my ducati i just take it to vee-two,world wide you cant get better,so im lucky they are local.i just want this bike to run good,im open to suggestions,believe me i have searched exhaustively on this site on this topic and have learned alot,but i am struggling a bit with this.i tried to do the chop test but the bike wont run hard at open throttle for more than 3 or 4 secondscheers lads,dave perth

 

[Cactus Jack]

Well you've already worked out that the air filters they come with are crap ...... .... I told Ken I didn't want one with my 28 OKO kit since I knew instinctively that they'd be no good just by looking at them ....... the dope assed flat metal on the end is a whacko idea and detrimental to air speed and flow .

Maylands sells genuine UNI Filters in 50 mm x 150 mm for $25 .......so one of those would be a start ..... I'm going to buy a few off him ....... Did your carb come with a 56-2 DC manifold ?

I haven't actually tried my OKO carb yet to know first hand how to get them working . I bought it out of curiosity . Mack has tried one on a stock 140 Lifan but with a 28 mm pipe . I do know that if your pipe is too small , you'll have no end to bogging when you hit the throttle hard because the flow right thru the engine will be slower reacting and the engines seem to get backed up . A bigger pipe and good port job gets things moving and reacting quicker ....... the throttle response comes to life ......

Sounds to me like it's not getting fuel when you open the throttle up due to loss of velocity and vacuum . Carbs rely on a strong vacuum signal to pull the fuel up the needle jet and spray it into the air stream . It needs to be atomised into a mist to make it into the cylinder rapidly ....... the finer the mist (to a certain point) the better the response and power ........ that's why the bigger 4 stroke MX bikes and even cars have accelerator pump carbs . It could well be that the 102 main jet is way too small ....... seems like the pilot is OK though .

First off , I'd check to make sure that all your fuel lines and tap are clear of crap and fuel flow from the tank is the best it can be , and also blow out all holes and jets in the carb to make sure there's nothing abnormal going on . Then I'd try different float levels to see if that makes any difference . Also , get someone to turn the throttle slowly so that you can see how high the slide is lifted before the engine bogs or dies .......

You can also put fuel in a squirt bottle to give the engine a shot of fuel at the bog point to see if it bogs worse or gets better ..... that way you'll know whether it needs to richened with a larger main jet ...... or made leaner .

If you had an old vacuum cleaner or something that blows air ..... you could hook it up to the inlet flange to bench test the carb off the bike . You watch how the fuel air mix is behaving as it exits the carb at different throttle points . Bill Jenkins the champion drag racer used to bench tune his Holley carbs that way on a flow bench ....... he'd also look at the fuel droplet size thru a magnifying glass . His engines flogged all others ........ it's amazing what that guy knew about everything .

Failing all that , all I've got to say is ....... this could be a job for ........ SUPERRRR MAAAACKKKKKK !!!!!!!!!!

 

[aussiemonster]

i think you are right about the pipe,i am going to buy a full on off road pipe,just to see what happens,because the pipe and muffler on it had to pass on road compliance,so it is a joke, as you can imagine,so i will do that ,cos as you say it is backing up and choking the whole engine,but the cops will be all over my ass,but 3 bolts later the original is back on.i had actually got the bike running very well with the original carb but with the big bore etc i figured i had to go up from what is a really just a 22mm carb.you are right about the manifold 56-2.it is better than the original only in that it is a 'longer' bend than what the bike came with.i appreciate you answering matey.cheers dave perth

 

[aussiemonster]

update so far is ... well the bike kept feeling like it was dying at top revs,so following the advice on this site this is what i did.i decided to first concentrate on the top end as that was the biggest problem,i put the needle on the highest clip position(so the needle is lower in the carb at full throttle)now the bike will rev out without feeling like it has hit the kill switch at full throttle,so im getting somewhere!
so did the chop test plug looks good tan sort of colour,all the way down in on the porcellain (spelling?,sorry).just to expirement i then put the air cleaner back on and sure enough at top revs it died,so air cleaner restrictive,as we all suspected(it is the one you get with the oko carb kit with the plate on the end)but it helped to confirm i was going in the right direction with all of this.just to refresh the carb has 102 mqin jet and a 39 pilot.
so i figure i need a smaller main jet cos you want to ideally be on the middle clip position.so i figure get hold of 2 or 3 sizes smaller and take it from there.
on to the pilot,jet and air screw,i found that it is at 2 and 3/4 out from bottom position and runs ok,so ineed to go down on the pilot as well,in fact the bike will run 'ok' with air screw right out,so that is where im at.so if i get 2 or 3 sizes down from the 39 it came with i should be getting close to ideal.cheers lads and as usual any and all opinions appreciated.cheers dave perth

 

[Mack]

just like cactus said I think your exhaust is forcing you to detune your carb just to get it to run. As with most things, you must make changes in multiple areas to acheive more power and smooth running. You really should get a big exhaust before you bother jetting that carb. Then I think you'll find you'll be going up in jet sizes. Otherwise you may as well just run the previous smaller carb that was matched better to the small exhaust.

 

[aussiemonster]

I think all said is spot on,because i have the bike running just right with 95 main jet,middle position on the needle and 35 primary jet.it is sharp responsive etc.But as you all say once i go up on the exhaust i will have to rejet,but i have done that many jet changes etc i'm comfortable with that.The big issue is i have to balance all this with what is socially acceptable,since i'm always screaming around the block etc,missus says its pretty loud on full song.The exhaust is the last part of this project,so i reckon i will have two exhaust systems,one for good power and response and one for the cops and the neighbourhood.
It has been fun,and i was very chuffed when i got the bike to work properly with jetting changes etc
Although i do think you have to compromise too much,meaning by the time it is all street legal there just i'snt any real fun power left.Just what i think,but.
Once everyone has learned to ride this with some sort of proficiency it will be on the market.But it was fun to play with carbies again,i actually got the whole thing right today,finally.
Cheers for all the help,dave perth

 

[Mack]

It is quite easy to make your own exhaust that is far quieter than anything out there yet performs better than anything out there..

 

[Cactus Jack]

Incidentally , I just bought a 26 mm OKO kit off DHZ and they NOW have a decent LARGE easy breathing foam air filter with them .....

 

[Worm]

Im a total noob when it comes to carbis etc..... but I noticed u said ur bike had a 26 carbi but its really a 22. Are they all like this? If so, what would be the correct carbi size for a 125cc lifan (black motor) with larger exhaust?

cheers

 

[Cactus Jack]

You measure how big a carb is thru the smallest point inside at the slide (thru the venturi) .... NOT at the rear outlet bore .......

If your 125 has a big valve head and a header pipe that's bigger inside than 26 mm .... then you can run a 26 mm round bore carb such as a VM-26 Mikuni , 26 mm OKO round bore carb or a 26 mm OKO flat slide carb .

The "30 mm" Mikuni oval bore carbs which are sold on ebay and come stock on most bikes are the equivalent of a round bore 26 mm venturi carb ........ and the "25 mm" Mikuni oval bore carbs are equal to a 22 mm venturi round bore carb ...... so even a 24 mm OKO is bigger and better flowing than a "25" Mikuni . The "30 Mikuni's" are silly because you have a 30 mm hole abruptly hitting a 26 mm hole in the manifold , a 26 mm head port , and a 23 mm valve throat ........ theoretically , a 24 mm round bore carb should work the best overall since they'd produce the greatest intake charge velocity and the 1 mm step all around would help block reverse flow (reversion pulses) under load ........ meaning the engine will have better bottom end throttle response and lugging power ......

Oval bore carbs are designed to block reversion pulses and sudden velocity drop by slowing down the rate at which the venturi area increases as the slide is lifted ......

 

[dirttau]

hey aussie where do u go riding in perth

 

[MasterSpoon]

Incidentally , I just bought a 26 mm OKO kit off DHZ and they NOW have a decent LARGE easy breathing foam air filter with them .....

hey sorry to bring up an old topic here but figured as this was already about the 26mm OKO carbs I would ask here.

Can anyone confirm what Cactus Jack has said here about DHZ suppling these with a decent foam air filter? I just looked at one of there auctions and it still shows a crappy filter.
KEIHIN REPLICA PWK 26mm FLATSLIDE CARBY KIT 140CC 125CC - eBay Other Makes, Bikes, Motorcycle Parts, Cars, Bikes, Boats. (end time 07-Jan-08 20:00:00 AEDST)
Also what size air filter do they actually take? can you get a genuine UNI filter for these or do you have to make up an adapter to make one fit?

thanks in advance
Wayne

 

[Cactus Jack]

The filter I got with my 26 OKO kit is about 48 mm I/D where it attaches to the carb flange which is 50 mm O/D , the foam section is about 92 mm in diameter with a 105 mm O/D prefilter sleeve over the outside , the foam is 70 mm long and is dark grey (almost black) , has fine pores , and there's no dicky metal plate , tapering , wire or paper crap to stuff up the airflow . I didn't get a filter with our 28 OKO kit since I didn't like the look of the filter pictured on DHZ's listing ....... but what he has pictured isn't necessarily what you'll get NOW ....... it's best to email Ken to ask .

The filter I got with the 26 OKO has zero resistance when you blow thru it mate ....... they breathe excellent .....

Maylands sells 50 mm UNI filters 150 mm long for $25 each + postage ...... I've looked up on the UNI Filter site and they don't state that they make them so maybe they're a special order ?????? ....

With UNI's (the green ones at least) , you have to keep them clean and properly oiled or they'll allow grit thru . As Cass has said , it's a good idea to keep several clean , oiled spare filters in sandwich bags in your car boot for regular filter changes to maintain peak performance throughout the day in super dusty conditions . A 150 mm long filter would obviously take twice as long to start blocking up and losing flow over a 70 mm long filter of the same diameter . The filter with the largest surface area is going to be the best to buy ........ as long as it fits the bike ........

 

[MasterSpoon]

much appreciated Mr Cactus Jack
that answered everything I needed to know and more.

 

[Mack]

I got one off DHZ in December and it had the shitty filter.

 

[MasterSpoon]

so best idea will be to email Ken to see what filters they are sending out.....
ahh good old hit and miss china parts. Will keep that in mind.

Btw Mack got any more details on this exhaust you speak of ?
I have been toying with the idea of making a dual setup for my bike for a while now for better flow and reduced noise but hopefully with a nicer note. I don't jump my bike so not worried about it getting hit or anything like that.

It is quite easy to make your own exhaust that is far quieter than anything out there yet performs better than anything out there..

 

[Mack]

I would stay single pipe. It is quite easy for anyone who can TIG weld to make a pipe. Or even if you can't, but pick things up quickly. You can purchase stainless pipe from most plumbing supplies. On average only need 1 x 180 degree bend and 3 x 90 degree bends and 2ft of straight pipe. Even off cuts from their scrap bin will do, as there are few sections longer than 150mm where there is no bend.
For the 140's I have been using 32mm pipe.
You can cut the end off your stock pipe for attaching to the head and heat with oxy and spread the pipe end out to match the 32mm pipe, or I prefer to have made machined stainless spigots shaped like this...

You then just slip the 180 bend onto this and TIG in place with a small fillet. The rest of the pipe then is a matter of cutting your bends and straights how you want. This can be fiddly but just take your time and use a flat surface to true up the ends of each section with belt sander or wet and dry, so they match up perfect. I tack the pieces as I go so they can be brocken apart if I am not happy with a section. You could even mark the rotation of each piece with permanent marker and tape up as you go, then take to a welder to finish. I true the joints well and then just fuse them together without filler. Anyone can do this. You just have to keep moving so as not to get any penetration or the pipe will have dags hanging into the pipe. To do it best you can plug the end of the pipe and feed inert gas into it (purge) to stop this. But I have not had problem with fusing well prepared pieces.

IMO -The secret to the end can is the gradual expansion of the pressure wave into the can via a cone and exit as well. It is my belief that this is having the same effect that open racing pipes with reverse cones does on the exhaust tuning and can be played with by trying different cone lengths and diametres etc. Otherwise with a straight cylindrical can the pressure wave expands instantly into a larger cylinder and gets partially trapped bouncing from front to back. I have had good success with stepping up just prior to the can to 48mm and then running this size right through the can to exit, matching the perforated stainless baffle exactly to the pipe aswell so there is no lip. The effect of this design seems to be also a softer and lower note but also performs very well.

 

[Cactus Jack]

I got one off DHZ in December and it had the shitty filter.

Here's a pic of the 26 OKO kit showing the better filter ........

http://www.miniriders.com.au/forum/...5107-postie-bike-oil-cooled-140cc-postie4.jpg

 

[phrozin]

hey sorry to bring up an old topic here but figured as this was already about the 26mm OKO carbs I would ask here.

Can anyone confirm what Cactus Jack has said here about DHZ suppling these with a decent foam air filter? I just looked at one of there auctions and it still shows a crappy filter.
KEIHIN REPLICA PWK 26mm FLATSLIDE CARBY KIT 140CC 125CC - eBay Other Makes, Bikes, Motorcycle Parts, Cars, Bikes, Boats. (end time 07-Jan-08 20:00:00 AEDST)
Also what size air filter do they actually take? can you get a genuine UNI filter for these or do you have to make up an adapter to make one fit?

thanks in advance
Wayne

I can confirm the filter is quite good with dhz oko kits shame the carbie was not as good, for all you guys wanting to get the oko carb a word of warning these carbs have not been drilled correctly and require moding to get rid of the bogging (flat spot) the pilot hole requires re drilling as does the air bleed.

For all the guys wanting to tune these things My 28mm was a shocker bogged off idle and missed like crap over 1/2 throttle and mine was on a 250 ohc big bore motor so air flow was not the issue, I have re drilled the pilot bypass hole with a 028" (may go tad bigger here .030" or .032")drill and main air by pass hole to .038" but works a treat atm and I run a 39 pilot jet and 130 main jet hauls ass now no bogging. Small carb I would drill the same with smaller main fitted 110 or 115 should work 120 for 28mm i feel would be a better choice hope that helps some of you guys tearing out your hair over oko flat slides or even better get a mikuni tm

 

[MasterSpoon]

ok got my OKO 26mm today
has a filter like these
http://home.exetel.com.au/miumiuxuxu1/DB/airfilterAB.jpg

anyone know what size jets is a good base to go from on these?
i'm changing from a "30mm" 26mm oval bore mikuni to a OKO 26mm D slide round bore. Mikuni currently has 105 main and 27.5 pilot

sorry forgot to add that it came with a K102 main and K37 pilot for the OKO