Flat Slide carby 28mm or 30mm

Find deals on amazon
Shop deals on ebay
Advertise with us
Mini Dirt Bikes & Pit Bikes Forum

Help Support Mini Dirt Bikes & Pit Bikes Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
crog

crog

Well-Known Member
Joined
Jun 17, 2007
Messages
77
Reaction score
0
Location
Outback Victoria
Hi i have a orion with a 125 ducar motor.
I was just wondering what would be better out of a 28mm flatslide or 30mm mikuni carby for it? Or can you even put either of them carbys on a ducar 125's?
cheers
 
Last edited:
Unless you have done some serious work to your top end both would be overkill, and your bike will probably be worse.
 
Agreed, you'd be better off sticking to the 25/26mm mikuni. You'd need some serious top end porting and work to make a 30mm carb really work.

You can however get a flat slide 24 and 26mm Keihin which I would imagine would be better.
 
Thanks i didnt think it would work.
Would ther be any better carbys that would make my bike go better?
Cheers
 
Probably not, if it has a Mikuni these are reasonable carbys if they are tuned correctly (they cop a lot of crap as people think that you need to upgrade your carby just for the sake of it).

If you want more power you really need to look at engine mods (port, valves, cam, compression, etc) or spend a few $$$ and wack a 140cc in it and start from there.
 
Yes , cass38a is right - the stock Mikunis aren't a bad carb ("30" = 26 mm ~ "25/26" = 22 mm) - they're just a bit awkward and hasslous to fine tune . A carb with a rubber mount is better because you can remove the entire carb off the manifold in seconds to work on it - plus adjust the idle air/fuel mixture easier from the side . There's no point in fitting a carb that is larger than the intake port and inlet manifold anyway . And usually when you add to the top - you lose off the bottom - which is detrimental to performance if your engine isn't bored , ported and cammed to rev higher - plus the gearing altered to work in with it all !

If you take a look at car carbs like Holleys etc - they are sized by CFM of airflow - NOT physical dimensions ! You calculate your engines' airflow requirements in the desired operating range - then select a carb with the precise CFM of airflow flow to match .

You'd use a 24 mm carb for all 'round torque , a 26 mm for the best of both worlds , and a 28 mm carb for midrange to top end perfomance - and I'm talking about ROUND BORE carbs - NOT oval bore carbs which are ALWAYS smaller than people THINK they are !! ~ even a genuine Honda 22 mm Keihin has a 24 mm outlet !
 
if anything go down a mm or so ,i recently changed my mikuni 25mm carb to a keihin flatslide 24mm pc carb out of a red barron boar kit and found the throttle response much more crisp and smoother as well as a more gutsy bottom end this was due to the inlet manifold being 24mm in diameter once I polished it up so that it matched the carb perfectly
 
30mm flatside

so if you had a 140cc lifan with no work done would a 30mm flatside be ok??:confused:
 
kwikaz said:
so if you had a 140cc lifan with no work done would a 30mm flatside be ok??:confused:
Click to expand...

NO it wouldn't be OK because the inlet manifold is 26 to 27 mm - the port is 26 mm - the valve throat is only about 23 to 24 mm - so you'd get a sudden velocity drop and BOG (that CAN'T be tuned out) everytime you opened the throttle quickly under load !

A 24 mm flatslide would work the absolute BEST for dirt riding - quick throttle response , strong pull under labour - still a decent top end ! If you're going to go bigger - you need an accelerator pump carb for it to work (FCR Keihin) like CRF150R's have !

Even 500 cc speedway bikes don't run a very big carb - around 34 mm !!!!!

The step up back into a smaller carb blocks reversion wave pulses which make the engine run rich down low - 2 strokes can run big carbs because they have a reed valve to block the reversion pulses . IF you have a 2 stroke or know anyone who does ~ get them to remove the reed petals from their reed valve then try running the bike and watch it run like a gutless soggy dog down low !!!!!!
 
Last edited:
ok might not get it now lol its a genuine one wats the differnce from the china one and this one.
 
30mm flatside

Cactus Jack said:
NO it wouldn't be OK because the inlet manifold is 26 to 27 mm - the port is 26 mm - the valve throat is only about 23 to 24 mm - so you'd get a sudden velocity drop and BOG (that CAN'T be tuned out) everytime you opened the throttle quickly under load !

A 24 mm flatslide would work the absolute BEST for dirt riding - quick throttle response , strong pull under labour - still a decent top end ! If you're going to go bigger - you need an accelerator pump carb for it to work (FCR Keihin) like CRF150R's have !

Even 500 cc speedway bikes don't run a very big carb - around 34 mm !!!!!

The step up back into a smaller carb blocks reversion wave pulses which make the engine run rich down low - 2 strokes can run big carbs because they have a reed valve to block the reversion pulses . IF you have a 2 stroke or know anyone who does ~ get them to remove the reed petals from their reed valve then try running the bike and watch it run like a gutless soggy dog down low !!!!!!
Click to expand...

so have you actually fitted one of these carbs to a 140cc lifan?? or are you just assuming that the motor would bog under load????
also you reccommended daniel40 to start with a lifan when he wanted to use a bigger carbie but then u tell me not to use a bigger carbie when i got a lifan?? p.s is this the carbie your talkn about ??

Monkeybike UK Keihin FCR28 Down Draft Carburettor
 
Last edited:
kwikaz said:
so have you actually fitted one of these carbs to a 140cc lifan?? or are you just assuming that the motor would bog under load????
also you reccommended daniel40 to start with a lifan when he wanted to use a bigger carbie but then u tell me not to use a bigger carbie when i got a lifan??
Click to expand...

I've bought a 28 mm OKO kit from DHZ to try out on a worked Lifan 140 - I haven't tried it yet because I'm still sorting out a cam , springs , oil coolers etc . I've talked to a lot of people and scanned the US sites thoroughly and they're recommending either the 26 OKO or 26 mm Mikuni ! I also bought a 26 mm Miconi carb off buythisdirtbike to try . I bought a 28 OKO because that's all I could get at the time and I ONLY paid $80 for the complete kit minus the air filter . (28 OKO , adaptor rubber , clamps , bolts , manifold , throttle cable) I'm expecting to end up selling the OKO and getting a smaller one from what I've read .

You have to ask yourself - "why is everyone getting rid of their 30 mm OKO's ???" Why did that guy try it on his engine to see "if it fits" then decide to sell it ??? If YOU put something new on your motor - would you take it off straight away and sell it if it worked without problems ????? Also - he MUST have a manifold and adaptor rubber - WHY isn't he selling those as well ???? I think you'll find the answer is that they've bought them - and couldn't get them to work without bogging - so they're selling them - but they're obviously keeping the manifold and adaptor rubber to use with a smaller carb - OKO 26 or VM Mikuni 26 .

I can tell you right now that you're wasting your time and money buying a carb WITHOUT the adaptor rubber and air filter - they take a filter with a 50 mm opening and both are hard to find .

At the end of the day - make up your own mind - this is only a forum and we are only trying to advise you not to make mistakes . You do what you want to - don't let anyone else tell you what to do . :) ;)

Some US links with info on OKO carbs :

How come all no name brands? - ThumperTalk
zongshen 125 dyno - ThumperTalk
zongshen 125 dyno - Page 2 - ThumperTalk
zongshen 125 dyno - Page 3 - ThumperTalk
 
kwikaz said:
so what would a 30mm flatside oko carb be good for then??? would it be ok for my 250cc?? eBay Australia: KEIHIN 30ML FLATSIDE CARBIE (item 140130242100, end time 23-Jun-07 06:51:02 AEST)
WHATS THE DEAL LOOK AT WHAT SIZE MOTORS HE SAYS TO USE THIS CARB WITH???
Click to expand...

The 30 OKO should work good on your 250 because the engine has enough airflow - just make sure the inlet manifold is also 30 mm inside to match . The ONLY way people are going to find out what we already know - is to try it for themselves ! When a carb is too big - you have to carefully control the throttle and ONLY snap it open when the engine is revving fast enough to handle it - then if you back off for turns - you can't just whack it open again without the engine hesitating and stumbling . In short - it PISSES you off and makes riding far less enjoyable .
 
Whew! So its a good thing I got meself a Mikuni 26mm carby ...

:)
 
Totally agree with what Cactus Jack says. the reason they sell bigger carbs, is because they can! It's a business. What are kids going to buy? bigger HAS to be better!

Well, no, not really. but people who don't know any better will buy them because they are bigger and sound better. A mistake anyone could make.

If I had a "fun" dit bike, I'd go a 24mm flat slide carb. Competition or higher spec bike 26mm. 28mm to me is just too much. Unless you had a full race spec 140 revving to over 12,000-13,000rpm. but that's a 1-2grand engine to build up, possibly more? I don't think any 'standard out of the box' engines are anywhere near this level of tune.

If you want performance, get yourself a higher compression piston, a cam and valves and that will give you the best gains. Then if you want to go further, porting, bigger valves etc.etc. and ONLY then will a bigger carb make a difference.

All IMHO of course :)
 
You must log in or register to reply here.

Latest posts

Back
Top