PDA

View Full Version : Keihin/oko 34 help needed



OGHAlex
05-05-2015, 05:08 AM
Hello.

Now ow I know the choice of 34mm carb for the rs 125 is normally a dellorto,
But I've managed to get my hands on a keihin/OKO 34 really cheap, and basically
brand new.

now can anyone help on jetting this?
thinking of
155(roughly) main
36(roughly) pilot
choke is one size I think?
needle and slide are correct
for the carb.

Im just not sure what's best, if anyone's had experience could they help?
Thanks.

Stuvvie
05-05-2015, 09:46 AM
Keihin isn't cheap, OKO is. They are normally ok, might require a bit of polishing to get the roughness off the surface but that's more racing related to get it to work close like a keihin.

Word of advice: Use keihin jets and not any of those cheap rubbish. Sizes can vary and a bad jet (by manufacturing faults or inaccurate sizing) could seize up your engine.

Jetting can vary and hard to tell due to it being a OKO but this is what a 34mm dell'orto stock carb runs with so I would start from there:

155 main

36 idle jet

1.5 turns out on the air screw

60 choke jet

k57 needle top notch

app 266 needle jet / atomiser

OGHAlex
05-05-2015, 01:20 PM
yeah the only reason im trying it as its cheap off of a friend, its brand new.. he just doesnt like it.
okay i've got the jet sizes written down etc ready for it, I'm going to order 155, 158 and 160 main.
36 and a 38 pilot.

The only questions i really have now are about the needle and atomiser.
should i stick with the oko needle or get a keihin? along with the corresponding slide of course.
and should i get the corresponding atomiser or just buy jets around the stock size of what is on the dellorto 34 and see what happens?

thanks again

L.T.R 250
05-05-2015, 04:03 PM
If your buying jets at like 155,158,160 as this is what a dellorto would run dont not a oko carb.

Keihin runs bigger sizes bet on a keihi on a rs you would run from a 180 to 220.

See what jets are in the oko and go from there if you not tested it yet why do you feel the need to change them already.

Got a mate with about 5 of these brand new what he had for years.

What did you pay for the carb

OGHAlex
05-05-2015, 04:48 PM
Well the jets that he got with the carb are
120,130 and 140 main
with 20 pilot jet
SOO that's probably the reason I want to buy jets..
before I start it and seize the dam thing haha!

I did the calculations to work out the main and it's supposedly 155 like a delly.
but if you're saying run bigger as its OKO (keihin rep Im guessing?)
what should I go for?

im certain 2005 honda cr 125's used keihin 36mm carbs (although that's only 2mm it obviously makes a difference)
but I believe their stock jets are 430 main 55 pilot.

I DIDNT KNOW CARBS WERE SO ANNOYING TO JET!!

my bikes having a new piston and rings when I come to jetting the carb, then after that a new exhaust,
in which I'll do plug chops once I've figured a jet to start from.
sorry to be such a pain it's just I don't really understand all this jetting malarkey, I have a good idea
how it works I just don't get why this carb would need such a large main?

Stuvvie
05-05-2015, 05:18 PM
Yeah OKO and Koso aswell come from the same factory (if I remember correctly), they are imitation Keihin's.

The reason for the difference is probably due to certain patents and ideology that make up a carburetor which doesn't necessarily make the one worse then the other. To see differences (and it's quite proper reading material aswell) I would advice to read this: thers125.blogspot.co.uk/2012/04/next.html (http://thers125.blogspot.co.uk/2012/04/next.html)

I have tried setting up my own engine with a Koso 34mm carb with a 155 main jet fitted and it bogged out due to being much too lean, as I had a 28mm dell'orto I chose to fit that first so I can't really help you on that sadly.

bassturbin
05-06-2015, 05:43 AM
Keihin isn't cheap, OKO is. They are normally ok, might require a bit of polishing to get the roughness off the surface but that's more racing related to get it to work close like a keihin.

Word of advice: Use keihin jets and not any of those cheap rubbish. Sizes can vary and a bad jet (by manufacturing faults or inaccurate sizing) could seize up your engine.

Jetting can vary and hard to tell due to it being a OKO but this is what a 34mm dell'orto stock carb runs with so I would start from there:

155 main

36 idle jet

1.5 turns out on the air screw

60 choke jet

k57 needle top notch

app 266 needle jet / atomiser



I use b35 idle jet and 155 main jet with rotax 122 and jolly exhaust 155 main jet is rich, up revs slowly reach and does not exceed 10.000 rpm after.Silencer outlet is oily and wet.I will test again with 150 main jet and b 36 idle jet...

I dont know but 155 main jet i think good with rotax 123, or air condition or gasoline makes a difference.

OGHAlex
05-06-2015, 06:23 AM
Obviously different engines react and behave differently to others..
so im seriously debating on buying every jet ranging from 150 to 200 or 220.
you can buy polini jet kits for keihin carbs.

obviously there is a cost implication as id need to buy pilot jets also and possibly choke jets.

the calculation of 34 x 5 x 0.9 (add .05 for exhaust and then again for airbox; aftermarket of course)
as I only have a piper cross filter with standard barrel, piston etc.. That would give me a main jet of 161.5
rounded up to a main of 162, okay so theoretically I should start at 160.

It it should act lean at high rpm, and then get richer and richer as I go through the jets, correct?

with all that being said is there a way to work out pilot jet? Or shall I just get some jets from 30-50
and put my needle on middle click and see which runs the best?

i think a case of trial, error and is in order to work this out. I just wish there was a rough number to start
with just like the delly 34.
ANY in advice or input is highly welcomed...
thanks

Stuvvie
05-06-2015, 05:04 PM
Don't worry too much about the idle and pilot jet. When running you prefer to be above the RPM where the powervalve is wide open as this is the most acceptable stage of this engine. Choke and pilot jet are mostly for starting and you will know right away when you want to set the idle rpm what is going on. Read the article I provided to know what happens exactly when it's too rich or too lean. I'd take the idle and choke jet in steps of 10 simply since it doesn't affect your performance while riding.

And yeah a standard setting is shit when not using dell'orto but that is simply because the 34mm dell'orto VHSB has been a standard item on certain years.

That being said, you got to start somewhere. Use the jets supplied, see if it starts and if it has power to pull away. If it starts with the choke skip that part and go for the higher rev ranges, follow the link I provided to set it up. If you want the easy way out have some motorcycle shop with a dyno and jets in stock help you out with a air/fuel meter.

That being said I find it a lot of fun to find a decent setup on my own by trial and error, this teaches you a lot about how a carburetor works. I just go for a spin with a spark plug socket, a small socket set and a few screwdrivers in my backpack to see what happens when you change stuff. Mostly around a road I know has a lot of places to pull off and tinker a bit, like with a easy accessible cyclist path or a B road next to it.

OGHAlex
05-07-2015, 03:10 AM
Okay all sounds good!
I shall order some jets tonight and hopefully if all goes well be able to start testing it next week.

For some reason my carb has the small button type jets and the keihin ones are hex head??
but anyway I'll order some dellorto ones as they're the same (flat head type)
I'm gonna whack the larger ones in first then it'll bog and I can work my way down, at least she
won't seize on me hahah!!

I'll do your method of taking some tools and a pocket full of jets and see where I end up!
but as long as it roughly idles that's fine, then sort the main and then the middle Rev range via the needle??

also I checked the float bowl and there is no choke jet, so unless it's inside the chock mechanism (for some reason?)
and the carb is premix only at the moment but I emailed the guy and he says that there's an oil passage
on top where it mounts to the inlet and all I have to do it drill and tap a thread for the union, correct?

i sound like a such a n00b but I just don't want to buy my new piston put it all back together with new jets
start it up and she seizes!!

thedots
05-07-2015, 03:38 AM
Hello, im also using mikuni carb on my rs, but its a tm 38-85. Pick it up with a current jet of main 260, pilot 37.5, slide 1-1/40, Needle 6fj40 middle notch.
for that my plug came out tanned.

Then I added a power jet
MaIn 170, pilot 10, power jet 80. For that my plug came out quite white but still feels rich on my wot.

Thats my base line hope it helps

Stuvvie
05-07-2015, 10:56 AM
I don't get why everyone feels so stupid when it comes to carbs. Really setting up a proper setup takes lot's of effort and practice to get it right. Don't feel bad about it, it takes lot's of reading and practice and the best way to do that is to use forums.

And I do like mixing my own fuel, I've had 2 huge seizes on my old RS50 due to failing oil pumps. Always carry a can of oil in the backpack and never looked back, I don't trust the darn things.

OGHAlex
05-07-2015, 11:11 AM
I don't get why everyone feels so stupid when it comes to carbs. Really setting up a proper setup takes lot's of effort and practice to get it right. Don't feel bad about it, it takes lot's of reading and practice and the best way to do that is to use forums.

And I do like mixing my own fuel, I've had 2 huge seizes on my old RS50 due to failing oil pumps. Always carry a can of oil in the backpack and never looked back, I don't trust the darn things.


Well I get the idea of jetting a carb and it's simple.
its just baffling how one 34mm carb would require certain
jets and then another would require different.
Okay it's to do with how it's made and how the air flows
etc etc...

But yeah I think I'm going to go pre mix, my friend is pre mix on his rs
and I like the idea of it, got premix on my yz also.

And I know it allows the oil to burn better as it emulsifies better and
it just darn smells good!!
AND yes the failing oil pump is a worry especially as they're plastic gears!

So without sounding stupid again, shall I get a jet kit or "jets" from 150 - 200?
and pilots from 30-60? Not every single one of course, lol.

Stuvvie
05-08-2015, 11:53 AM
In steps of 10 is always a good idea to start with. Maybe range it a bit further like LTR250 said...like towards 220 and see what it runs best with. Then you have a starting point and you'll realize soon enough if it's too big or not!

OGHAlex
05-12-2015, 09:59 AM
Okay thanks for the input guys it has helped a lot!
I have done some more research and apparently keihin/OKO carbs
tend to indicate lean symptoms when running rich (which sounds
an absolute bundle of fun)

But anyway with that being said I'm hoping plug chops are going to help,
im expecting black plugs or black ish (or I put the biggest in an it's magically
cardboard brown) with a jet around 200 and going white towards 155.


I shall all update with any problems that occur as no doubt there will be,
wish me luck

OGHAlex
05-20-2015, 07:40 AM
UPDATE!!

i have the carb in the bike and it has a 200 main and 58 pilot, 2nd from top clip on needle.

it pulls away fairly nicely then splutters from around 1/4 to 3/4 and then is smooth but doesn't pick up quickly.
i did have a 205 main in but the 200 feels better.
the top needle clip doesn't make a huge difference and 3rd clip makes it worse (so far).

i have established that is all running rich along the spectrum. Going to try a smaller pilot and a smaller main and see how I get on.

any help welcomed

EDIT: I know it's rich when it splutters as if I put the choke on it makes it a hell of a
lot worse. And I have mixed oil at just over 33:1 (more oil) for the first tank as it has brand new piston and rings in.

EDIT 2: i have found that bottom clip makes it ridiculously splutterry and top clip better, but marginally.
So im going to buy this needle set; http://www.lambrettaspares.com/spares/bgm-parts/needle-set-%28kit%29-pwk-type-for-24,-28-and-30mm-carbs-%28hkj-to-klk%29-bgm/mbgm0053s.html

im hoping these will work as my needle doesn't have any markings on, but there are these type which are pointy and thin and keihin do another type which is like a dellorto needle which in comparison is fat and thick.

The ones ive linked are the same shape etc as my current one just obviously with different specs.