KOSO 30mm carb

tiba_karotsu

OVERREV TUNING
#1
It's pretty hard to get one of these now that scooterracing has taken a backseat to 4strokes (they suck!!) but who cares about them they wouldn't hold a candle next to our race scooters.





it comes with a few jets (38, 40, 42 pilot jet & 135, 138, 140 main jets) but even the 140 isn't big enough for my set-up it was running lean so i had to drill jets for it to work properly.

also the stock needle sucks even at the leanest setting it was still running too rich so i had to transfer my Keihin needle from the OKO to the KOSO & it worked like a charm, now only the pilot jet remains it's still running rich at idle so i'll try decresing it from 40 to 38 but i think a 35 would be perfect i want a crisp, clean throttle response.

you'd think the 70cc would lose power when using a bigger 30mm carb but in this case it's the opposite, the scooters' now very hard to keep the front tire down & even with heavy rollers (25,4 grams total) which are suited for my lightweight rider it's pulling me like i was 45kgs (i weigh 70kgs), i had to retune my MRD manifold to accomodate the bigger carb but it still clears the frame but not too much (on bigger scooters like the Ark or Aerox this won't be a problem).

initial impressions with the big carb are very good i feel i'm going in the right direction in tuning this new engine set-up maybe there's a chance that a 70cc can win some races against 100cc Dio G strokers, until the 2F4R kit arrives i'll be refining this set-up more & make them go nuts about how they can make their scooters faster without blowing them up in 2 runs. :D
 
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Browni

B.A.T tuning
#3
tiba_karotsu said:
It's pretty hard to get one of these now that scooterracing has taken a backseat to 4strokes (they suck!!) but who cares about them they wouldn't hold a candle next to our race scooters.

it comes with a few jets (38, 40, 42 pilot jet & 135, 138, 140 main jets) but even the 140 isn't big enough for my set-up it was running lean so i had to drill jets for it to work properly.

also the stock needle sucks even at the leanest setting it was still running too rich so i had to transfer my Keihin needle from the OKO to the KOSO & it worked like a charm, now only the pilot jet remains it's still running rich at idle so i'll try decresing it from 40 to 38 but i think a 35 would be perfect i want a crisp, clean throttle response.

you'd think the 70cc would lose power when using a bigger 30mm carb but in this case it's the opposite, the scooters' now very hard to keep the front tire down & even with heavy rollers (25,4 grams total) which are suited for my lightweight rider it's pulling me like i was 45kgs (i weigh 70kgs), i had to retune my MRD manifold to accomodate the bigger carb but it still clears the frame but not too much (on bigger scooters like the Ark or Aerox this won't be a problem).

initial impressions with the big carb are very good i feel i'm going in the right direction in tuning this new engine set-up maybe there's a chance that a 70cc can win some races against 100cc Dio G strokers, until the 2F4R kit arrives i'll be refining this set-up more & make them go nuts about how they can make their scooters faster without blowing them up in 2 runs. :D
Nobody said 30 mm is too much for 70-80cc scooter :)

I had problem with the needle when I adjuted the Koso karb too my 180 cc engine, I made totally custom profile needle know it's perfect! :)
 
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tiba_karotsu

OVERREV TUNING
#4
Big B NRG said:
Sounds nice, but why didn't you go for the 32 mm Koso?
And why did you bought a Koso and not a 30 mm OKO?
B'coz the OKO 30mm carb isn't a true 30mm it's 30mm from top to bottom & 28mm from side to side which only gives a mean area of 29mm, also the KOSO has a bigger float bowl which holds more fuel so less chance of running out of fuel during the race.

KOSO carbs are very hard to find like i said before & i'll be hardfpressed to find a manifold that i can port to that size i'm lucky i have bought an MRD manifold which's a good match to the 30mm carb but it also required some tuning to match to the VL14 reedvalve.

Well maybe if i was running a 2F4R or a rebored MHR Team 80cc i'd probably have gotten a 32mm if the manifold was available for it but since there isn't any available here i went for the 30.
 

Joël

Weight kills accel
#6
I've tested the Koso30 on my 2fast4race engine too, and used a Malossi 30mm manifold for MTX80. The results in power are pretty much the same as my Keihin PWK28, only the Koso has the annoyingly quality that it leanes off at higher rpm.
Sure this can be corrected with needle jets, needles, main and slow jets but it's good to know it isn't a plug en play carb like the Keihin.

I must say that the carb looks really nice and can be put under a steep angle without flooding, but why the heck did they make the throttle valve 38 mm?!
 

tiba_karotsu

OVERREV TUNING
#7
rydah said:
koso 30's are common out here tiba.
Not here they ain't, the most common are the OKO & you know me i like to run parts that aren't commonly used by others to set myself apart, yes this carb is a headache to tune i have found out the problem why so many here gave up on this carb, i finally managed to get the engine to idle on this carb there was an airleak past the o-rings on the jet block that's why it's so screwy.

i will post movies of my test runs here for y'all to see, the first one's with the carb still having part-throttle response problems & the second one has the problem solved & the engine is now idling stabley.
 
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tiba_karotsu

OVERREV TUNING
#8
Joël said:
I've tested the Koso30 on my 2fast4race engine too, and used a Malossi 30mm manifold for MTX80. The results in power are pretty much the same as my Keihin PWK28, only the Koso has the annoyingly quality that it leanes off at higher rpm.
Sure this can be corrected with needle jets, needles, main and slow jets but it's good to know it isn't a plug en play carb like the Keihin.

I must say that the carb looks really nice and can be put under a steep angle without flooding, but why the heck did they make the throttle valve 38 mm?!
sure beats me why they made it that large but i'm planning to have turned on a draaibank to reduce the size to fit my MRD manifold it's stretching it too much when i put it on everytime.

it's a good thing carb parts from the OKO & Keihin fit right in i think i know why that problem occurs & it could be also related to the air leaking past the o-rings in the carb you might want to check that out.
 

Browni

B.A.T tuning
#9
Joël said:
I've tested the Koso30 on my 2fast4race engine too, and used a Malossi 30mm manifold for MTX80. The results in power are pretty much the same as my Keihin PWK28, only the Koso has the annoyingly quality that it leanes off at higher rpm.
Sure this can be corrected with needle jets, needles, main and slow jets but it's good to know it isn't a plug en play carb like the Keihin.

I must say that the carb looks really nice and can be put under a steep angle without flooding, but why the heck did they make the throttle valve 38 mm?!

I think bexause they use the same casting for the 28 and for the 34 mm carbs too only the text is different. And they use the same throttle bodies. But this is my tip!
 
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