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 MK2 sport pro, 24mm Polini carb, Yasuni C16. polini air filt 
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Joined: Mon Jun 19, 2017 12:15 am
Posts: 23
Location: Reno, NV
scooters and mods: 2004 Zuma
Post MK2 sport pro, 24mm Polini carb, Yasuni C16. polini air filt
I recently got a new 24mm Polini Carb and it's a puppy to Tune. Currently, I have a 124 Main Jet and a 45 Pilot Jet in and it's been having some issues. What would a good starting Point be, as far as Jet sizes go for the Main and the Pilot? I tried going down in size to a 116 and a 110 and had no luck whatsoever. Seems Sort of sputtery, especially at lower RPMs and does not seem to want to kick into the power band. I will have to check what RPM it does not want to go past. But it's right before the Powerband kicks in and the exhaust starts to do its job. It feels Almost un-rideable. It is super cold currently where I am so I have one side of the Radiator duck tapped off so I can try to get it somewhat up to temperature. The absolute highest temperature I have seen was 125 Farenheight so far.

Current Setup:

10mm Malossi Crank
10mm LC Stage 6 MK2 Sport Pro
24mm Polini Carb | 124 Main | 45 Pilot
Stage 6 Reed
Yasuni C16 Racing (de-restricted don't get it twisted)
Naraku Intake
Malossi Overrange Variator Kit LA Furia Rossa
Stage 6 Clutch
Stage 6 Bell
Polini Open air Filter
BPRH9ES (Something like that)

If anyone could give me a good starting point as what jet sizes to get for this 24mm Carb. Looks like it's going to be a pain in the butt to tune.

Any insight would be helpful

2004 Yamaha Zuma

~ Malossi RHQ Crankshaft 10mm
~ LC Stage 6 MK2 Racing
~ Bolt-On Radiator Set Yamaha BWS/Zuma 2002-2011
~ Motoforce Racing 12v Water Pump
~ Yasuni C21
~ Polini 24mm Carb | #122 Main Jet | 45 Pilot
~ Polini Gear Set 13/44
~ Malossi Overrange Variator Kit LA Furia Rossa 6x 3.5g rollers
~ Stage 6 Mk2 Clutch/ White contra, red springs engaging @ 7200rpm
~ Stage 6 R/T Clutch Bell
~ Naraku 35mm Intake
~ Stage6 V-Force3 Reed Valve
~ Polini Air Filter (pod/ open)
~ Doppler Racing Shock Absorber (275mm)
~ Shock Riser
~ MVT Digital Direct Ignition @ .35 BTDC
~ NGK BPR8ES Spark plug
~ NYC Quick Throttle
~ LED Headlight Mod
~ Trail Tech Vapor RPM meter
~ Trail Tech Temp gauge

Fri Mar 15, 2019 6:01 am
Scooter Addict

Joined: Fri Apr 12, 2019 6:04 am
Posts: 138
scooters and mods: 1998 Zuma Prebug
Post Re: MK2 sport pro, 24mm Polini carb, Yasuni C16. polini air
I think 24mm is gonna be a super hard one to tune. I think people said to choose between 17.5-21mm max. I wouls have no clue how to tune something that big but I reckon you'll have to get a different size carb to tune a bit easier with this setup. Also can I ask what top speeds you are reaching with your setup?

'98 Zuma Prebug

70cc Athena w/ BR9HS, 17.5mm Carb (82MJ, clip 1 from bottom), 9.9:1 final drive, 4.4g rollers, LV 5k clutch springs, LV TT Pipe

Current max speed ~93kmh(58mph) @ 9.7k rpm

Build Project: viewtopic.php?f=48&t=28663

Sun Jun 16, 2019 5:27 am
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Joined: Wed Mar 16, 2011 9:25 pm
Posts: 742
Post Re: MK2 sport pro, 24mm Polini carb, Yasuni C16. polini air
You say you're "having some issues" but that doesn't really say much. But I'll go out on a limb and hypothesize that you're generally not getting good power. Maybe you get rolling at first, but then you hit a dead spot on the throttle.

Try this little experiment. Get a bowl, fill it with water. Take a straw, and blow air through the straw, perpendicular to the water surface. Notice the way the air moves the water. Then, ditch the straw, hold your face right over the bowl, open your mouth as wide as you can, and blow air out of your mouth as forcefully as you can, once again perpendicular to the water surface. Take note of how much the water moves this time.

That is what you're doing to your fuel delivery when you get a bigger carb. The bigger it is, the slower the air flow will be. Too big, and you deliver very little fuel into the cylinder.

Stock '05 Zuma - in the wild somewhere.
2015 Zuma - Stock. For now.

Mon Jun 17, 2019 8:24 am
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