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Old 10-19-2013, 06:09 PM   #1
mopedhi   mopedhi is offline
 
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bogs down with UNI filter

My scooter bogs down at higher speeds with a uni filter but does fine with the stock airbox. It has an 85 main jet. Should I get a mikuni carb or 28 oko carb?

vento zip 2 stroke
70cc bbk
stock carburetor
stock exhaust pipe



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Old 10-19-2013, 11:02 PM   #2
qwertydude   qwertydude is offline
 
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85 main jet is too small. Generally open type filters need bigger ones. anywhere from 88 to 95 has been my experience. Bigger carbs on a 50cc is pointless and make it even more difficult to tune.

Also you'll need to experiment with needle height, maybe lower the clip a notch or add a shim depending on the needle type. And reset the mixture screw using the idle drop method.
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Old 10-21-2013, 08:14 AM   #3
blueboy5000   blueboy5000 is offline
 
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+1 To Qwerty.

Often, I have to use tape to restrict uni-filters on 50cc's, even with 88 to 95 jets, to create a richer mixture.

A 70cc should use a 19mm carb at the LARGEST, a 28 is too big for even a BBK'ed 150cc.
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2011 Roketa MC-23-150

4T 150cc 157 qmj

24mm carb w 115 main jet and paper cone air filter

Manual petcock w Tygon fuel lines

Scrappy Dog Scooters Retro-slash stainless straight-thru exhaust

RED spring clutch

Adjustable CDI (brand unknown, it's blue and red and works great!)

KOSO high performance variator w 12g sliders

Gates Powerlink 835-20-30 belt

GPS verified 65mph on flats.



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Old 10-24-2013, 01:57 AM   #4
skuttadawg   skuttadawg is offline
 
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I use a 120 MJ with BBK , pipe and Uni on my 2T . A 28mm is too big . The power kits come with a 21mm . I use a 19mm TK carb and it runs like a beast . Get a jet kit like this http://www.partsforscooters.com/114-...ategory=133078
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Old 10-24-2013, 10:48 PM   #5
mopedhi   mopedhi is offline
 
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Quote:
Originally Posted by skuttadawg View Post
I use a 120 MJ with BBK , pipe and Uni on my 2T . A 28mm is too big . The power kits come with a 21mm . I use a 19mm TK carb and it runs like a beast . Get a jet kit like this http://www.partsforscooters.com/114-...ategory=133078
I already have that kit 10 pieces.
I bought a used leo vince zx pipe now it went from 30mph to 45mph with the pipe and 70cc bbk.
Before it only went 30mph even with the 70cc bbk installed.
Now I know the only thing holding the scooter back is the stock carburetor.

Vento zip gt5 2t
70cc bbk
leo vince zx pipe
stock carb w/airbox
5g rollers
tops 45 mph



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Old 10-26-2013, 05:43 PM   #6
Snek   Snek is offline
 
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Go with a bigger main jet, try 5 sizes higher. I've tried 10 sizes higher with an open air-filter, was to much!
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Old 10-26-2013, 06:24 PM   #7
mopedhi   mopedhi is offline
 
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I tried with 90,95,100,105,110 and 115 main jet. It just sputters with the airbox and it went slower with the UNI filter.

Raising the needle did nothing but it did fill up the bowl quicker

Vento zip gt5 2t
70cc bbk
leo vince zx pipe
stock carb w/airbox
12g rollers
85 main jet
tops 48 mph GPS
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Old 11-09-2013, 01:09 AM   #8
skuttadawg   skuttadawg is offline
 
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Too big it will sputter as I tested a few jets on my build . How many MM is your carb ? Did it have the variator washer which limits the speed removed ? I also replaced the 40 idle jet with a 45 IJ in my 19mm TK carb and it really improved starting and idle . I bought some jets here since I could not find a jet kit at that time for my carb http://www.jetsrus.com/a_jets_by_car...11-22_main.htm Remove the sparkplug and compare it to this chart http://www.4secondsflat.com/plug_chart.html If you change out the jet again get a new sparkplug , run it at WOT while riding and let it hit max RPM then hit the kill switch and inspect the spark plug color again to see how the new jetting is .

I replaced the 68 MJ with a 75 and it ran great when it was new and still a 50 . I bought a Uni vent cover which is smaller than the big red Uni airfilter and went with a 90 MJ . It ran great as bottom end and midrange were better with the same top end . Well I later bought the Uni airfilter and my dealer and no other shop in town had anything in my jet size bigger than a 90 . I started it up and it only had a slight bog but nothing like it was going to stall . Being impatient and anxious I wanted only to ride around the block to test it . Well dang it I had a seize and it melted the prong off of the sparkplug . I have never had this happen with all of my many years of riding and modding two wheelers .

When I put on the 70cc BBK I also put on a PM Racing pipe and first tried the small Uni vent cover it sputtered so bad I could not ride it with a 140 . I put on the proper Uni it was better . I tried a 130 it sputtered but not as much . A 120 MJ it was great . The PM Racing pipe was not restricted like the stock pipe so I lost backpressure and takeoff power but midrange and top end it was beasty . With a 2T you always want to run just a hair rich rather than be dead on it to avoid a soft seize . When my 50 seized it fried it . I did have a mild soft seize with the BBK while testing a 105 MJ but after a few minutes it fired up and I rode it home while being easy on it . I also went from running a NGK BRP(7)HIX to the (8) version which is a cooler heat range .

You may get a gain by replacing the intake with a Hoca intake with carbon fiber reeds . It should have a bigger venturi , CF reeds respond better than the stock metal ones which have been known to break and eat up the soft piston .

I put in Hoca 1.5k clutch springs so the clutch engages at 1.5k higher RPMs than the stock springs to help on take off . It came with 6g rollers and I tried 4g but they were too light so I mixed them to equal 5g when it was a 50 cc . With the BBK I could redline while going up a tall and steep hill . I put in 8g DR Pulley sliders since I loved how they performed in my Echarm and I wanted heavier weight to try to keep from over revving . Well takeoff was less , midrange just a hair less but top end was faster ( only registers 50MPH and it goes beyond the gauge ) but still would scream when I went above 50 MPH even uphill with a running start . So I will have to get taller gears and lighter sliders . I also put in a Hoca BB torque spring base which has BBs that prevent the torque spring from binding and it seems like I have more " gear shifts " and the shifts are more smoother too . http://www.partsforscooters.com/169-...category=74117 I tried to put on a Hoca 1.5k torque spring but I could not get it to compress enough by hand so I reused the stock one
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Old 11-09-2013, 03:04 PM   #9
Lefty   Lefty is offline
 
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Just to clarify for some that may not know RAISING the needle does nothing to fill the carb bowl with more fuel. Raising or Lowering the needle adjusts the mid-range amount of fuel it gets If that is where the motor is acting up.

If the scoot is doing 45 with a 70cc bbk that is fantastic. People put in 80bbks to get to that speed. I think your there already and it has no more top end unless you put in taller gears to turn your wheel faster.
Lefty
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Old 01-18-2017, 06:49 PM   #10
DisillusionedPrepper   DisillusionedPrepper is offline
 
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I was looking for info on how many people on this forum had experience with 28mm Flatslide vs CVK type carbs on the 150-250cc engines. Reason is I am going to stroke my engine, and tighten it up (blueprint) for higher reving (8-9.5k).
I know this thread is older but I have to "correct something.
I set up a Kymco ZX50 several years ago for land speed record runs. Still have the bike, and still ride it from time to time.My best speed to date was 87.3 MPH, and there is still tuning room for improvement.
For LSR runs I set the gear box at a 6:1 final drive ratio. It eats up a Stage6 MKII clutch in thee / one mile runs. Now I have it at 7:1 for street use, and I get around 60-70 miles out of the same clutch.
The bike is 73.4cc, with a Polini top end. The cases have been flow ported, Ruima 4mm stroker crank, custom pipe, ect...

Point is I run a 28mm OKO flatslide on this bike. RPM is the determining factor in what size carb to use. Not cc's

If you set up a 4 stroke to run higher rpm's (8k ish) a larger carb (28mm) will work. In fact it is needed. The only reason to set up a high reving engine is to pump more air faster. The only way to achieve this is to go larger on the intake system.

Now granted, on a putt around town 50-250cc bike the 28mm carb may be too large. I just wanted to add another point of view to this older thread, and perhaps give some food for thought.

If anyone is running a flatslide on their 150, I would sure love to hear about how it is working out.
Trial, and error is one thing but that's why forums exist. Experience rules!!!
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