26mm Vs 30mm Carby

[zaffa86]

Is there any advantage to running a bigger carby on Lifan 140cc.

Currently it is just standard but is being fitted with lightweight magneto, Hi Rev CDI during the week. I also plan to change the cam soon.

So what I would like to know is there any advantage to running the bigger carby over the 26 mm. Or would it just be pumping to much fuel for the engine to handles?

Thanks in advance for any help..

 

[roost666]

go the 26mm mate it will be a better all round carb, i think 30mm would be to big for a 140 and would just push way to much fuel in but i could be wrong, a 28mm might be better, i think a 28mm will give you lots of punch in the higher revs but will be rather boggy down low, where the 26mm would be good all round i THINK only goin off what i have read. hope that helps

 

[zaffa86]

Thanks for your response looks like i'll be sticking with what I got

 

[Shing]

Sorry for the off topic, but. What is the light weight magneto? What does it do, where does it go and is it a worthy upgrade?

 

[roost666]

its called a inner rotor kit.......you remove your flywheel and install the IRK it will give you a more responsive rev range(will rev out faster) if you use the search funtion you will find a tonne of threads with loads of info on them

 

[Cactus Jack]

When he refers to "26 mm carb vs 30 mm carb" ... I'll bet he's talking about Mikuni oval bore carbs !

A 26 mm oval bore Mikuni is actually a 22 mm carb and the 30 mm oval bore Mikuni is actually a 26 mm carb ... A 26 mm round bore OKO flat slide carb will give better performance than both of those carbs ... but the VM-24 round bore Mikunis are reported to work extremely well everywhere ... IF you go too big with the carb venturi the engine becomes more sensitve to quick slide opening ...

 

[01nutracing]

Hey Cactus do you know a good starting piont for jets on the OKO you mentioned? Its for the 140 at not that much above sea level. Is there some guide on the net ?

 

[Cactus Jack]

A 140/150 China engine w/ 26 mm round bore carb would be somewhere between these ... Your best bet would be to buy the TB OKO 26 pilot and main jet kits then start doing some testing and tuning on a straight road or track ... Do some throttle chop / plug read runs with the needle clip in the middle position first to get the main jet right ... then do the pilot and air mixture screw ... then mess with the needle clip position IF necessary ... Forget trying to tune it so that you can snap the throttle wide open quickly at idle without the engine dying ... it aint gunna happen without resorting to an expensive accelerator pump carb ... and IF you fit a huge pilot to make up for the lack of an accelerator pump you'll have a dog sluggish engine down low ...

XL/CB125 ......... (#38 pilot #100/#102 main - 22 mm Keihin )

XL 175 .............(#40 pilot #110 main in a 26 mm Keihin)

 

[zaffa86]

I have heard VM24 are they way to go they are 28mm flat slide.... will be getting one this week

 

[Mack]

hey all, 26mm oko is best budget carb for the 140 I have found. You can help the snap off 1/4 throttle by fitting a better tapered needle. This is how you feed a bit more juice low down without upsetting the main jetting.

I may have said before, but I also use the 26 oko for specially built motors upto 160cc. For anyone who wants to put in a little effort, a 26mm oko ported and reamed out to 29mm in the top 2/3 of the throat and properly jetted and with the right fat needle is killer. Three carbys in one.

 

[Cactus Jack]

Howdy Mack ... It's great to see you posting again ... Yes I've directed people to your post on pipes , your muffler and ported 26 mm OKO's a few times and I've got it saved myself for when I get around to doing it ... What needle do you use ... One out of a Keihin PWK 28 ? ... Do you have a part number ? ...

Most of the bikes come stock with 32 mm header pipes now and some of the mufflers are built almost how you've described .... I went to the Jam and most of the winning bikes had OKO 26 flat slide carbs on 'em ...

Your pipe info ...

http://www.miniriders.com.au/tech-talk/14947-carby-situation-guidelines-needed-2.html

Your carb info ...

http://www.miniriders.com.au/tech-talk/14947-carby-situation-guidelines-needed-3.html

 

[Mack]

hey sorry for the delay... the needles are swapable for a range of keihan carbs. They have three letter codes stamped on the side for taper and diametre measurments. I think the stock ones are JJH. There are needle guides online somewhere...I have used a couple of sizes up and combined with porting eliminated any hesitation. The slide cutaway is s'posed to have even greater effect on off idle snap but I found success with the slides as they came.

 

[themountain]

here is a link about the different needles...its a german site but the info is in english
KEIHIN Rennvergaser: FCR, CR special, PWK, PWM, PE, PJ - Produkte - Nadeln - P-Serie

 

[Cactus Jack]

Thanks for that mountain ... I've book marked it for future reference ...