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 Yamaha 1998 acceleration and top speed issue 
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Bronze Member
Bronze Member

Joined: Fri Aug 31, 2018 5:18 pm
Posts: 405
Location: Fox Valley Wisconsin
scooters and mods: 2 2004 Vinos 2004 Zuma
Post Re: Yamaha 1998 acceleration and top speed issue
post your sig line up as you mod so others can chime in and help

_________________
2004 Vinos Derestricted exhaust and variator stock carb with mikuni 70 main jet needle down 1 clip 40 mph
Athena Sport BBK waiting to go on

2004 Vino Malossi sport 70cc Malossi Wild Lion pipe derestricted stock variator stock carb 72 mikuni main one clip rich
45 mph still breaking in Michelin S1 90/90/10 rear tire Michelin S1 3" x 10 up front

2004 Zuma Malossi sport 70 cc Technigas next r 2008 zuma torque driver polini high speed variator 5.5 grams sliders malossi delta clutch yellow contra yellow clutch springs Stock Carb 82 main jet 46 pilot jet needle 1 clip rich stock athena 14/42 gears 11 to 1 final ratio 56 mph

2005 Eton Beamer (Taiwan Zuma Clone) Airsal sport 70cc 9200 peak rpm top speed 42 77.5 mikuni jet needle 1 clip rich


Wed Apr 17, 2019 8:02 pm
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Scooterologist

Joined: Fri Apr 12, 2019 6:04 am
Posts: 109
scooters and mods: 1998 Zuma Prebug
Post Re: Yamaha 1998 acceleration and top speed issue
zino18 wrote:
You posted while I was typing .
Jets are so cheap you might as well have the perfect ones for your set up and where you ride elevtion and temature range wise



I was scrolling through the forums and saw that jmkjr72 said "the prebug runs a 12 mm carb and it is too small to run with a bbk you need a larger carb". I am not sure if I should bother trying to upjet and just get a 19mm carb.

Anyways here is some info I have gathered. I found out that the main jet was a #90 and the pilot jet was a #50. What sizes do you recommend for me? (I am +20m above sea level and am in a pretty hot area like 30 degrees C).
I also saw that the spark plug installed was a BPR6HS whereas stock is supposed to be BR8HS. Here is a pic of the spark plug. https://imgur.com/a/LYT69ce I think this may have been affecting my zuma quite a bit.

_________________
'98 Zuma Prebug
-70cc Athena BBK (BR9HS plug)
-Stage6 Straight Cut 14/42 Gears -> 9.9 : 1 final drive
-Stock variator (6g rollers -> 8mm sharpie test)
-17.5mm Dellorto Carb (84MJ, clip in middle position)

Current max speed ~67kmh (GPS verified)

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


Wed Apr 17, 2019 10:09 pm
Profile
Scooterologist

Joined: Fri Apr 12, 2019 6:04 am
Posts: 109
scooters and mods: 1998 Zuma Prebug
Post Re: Yamaha 1998 acceleration and top speed issue
I went ahead and bought a 17.5mm dellorto one which comes ready for manual choke for decently cheap.

https://www.scootertuning.ca/en/carbure ... &results=1

It comes with a 90 MJ so I think that will be fine right?

_________________
'98 Zuma Prebug
-70cc Athena BBK (BR9HS plug)
-Stage6 Straight Cut 14/42 Gears -> 9.9 : 1 final drive
-Stock variator (6g rollers -> 8mm sharpie test)
-17.5mm Dellorto Carb (84MJ, clip in middle position)

Current max speed ~67kmh (GPS verified)

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


Wed Apr 17, 2019 11:51 pm
Profile
Bronze Member
Bronze Member

Joined: Fri Aug 31, 2018 5:18 pm
Posts: 405
Location: Fox Valley Wisconsin
scooters and mods: 2 2004 Vinos 2004 Zuma
Post Re: Yamaha 1998 acceleration and top speed issue
PLugs are a performance part for a 2 stroke so the right one is critical .
That one by the look of it is holding you back.
The 6 is hotter than the 7
The 9 is correct plug for aluminum kit like the athena it is a cooler plug .
I still like to have extra jets just to dial it in closer
It also helps to know what way too rich sounds and feels like and as you drop jets wht going lean sounds like.
As long as you can get them locally or through ebay .
plug chop will tell you if you are close enough.
That is a very good vendor to buy from
Jmkr is a very good tuner so folowing his advice will serve you well.

_________________
2004 Vinos Derestricted exhaust and variator stock carb with mikuni 70 main jet needle down 1 clip 40 mph
Athena Sport BBK waiting to go on

2004 Vino Malossi sport 70cc Malossi Wild Lion pipe derestricted stock variator stock carb 72 mikuni main one clip rich
45 mph still breaking in Michelin S1 90/90/10 rear tire Michelin S1 3" x 10 up front

2004 Zuma Malossi sport 70 cc Technigas next r 2008 zuma torque driver polini high speed variator 5.5 grams sliders malossi delta clutch yellow contra yellow clutch springs Stock Carb 82 main jet 46 pilot jet needle 1 clip rich stock athena 14/42 gears 11 to 1 final ratio 56 mph

2005 Eton Beamer (Taiwan Zuma Clone) Airsal sport 70cc 9200 peak rpm top speed 42 77.5 mikuni jet needle 1 clip rich


Thu Apr 18, 2019 6:12 am
Profile
Scooterologist

Joined: Fri Apr 12, 2019 6:04 am
Posts: 109
scooters and mods: 1998 Zuma Prebug
Post Re: Yamaha 1998 acceleration and top speed issue
Btw to everyone who is reading this I foudn the issue. The oil feed line was cracked and so the piston was never getting lubricated hence it seized so many times. I've fixed it now and you can continue reading about my project here. viewtopic.php?f=48&t=28663

_________________
'98 Zuma Prebug
-70cc Athena BBK (BR9HS plug)
-Stage6 Straight Cut 14/42 Gears -> 9.9 : 1 final drive
-Stock variator (6g rollers -> 8mm sharpie test)
-17.5mm Dellorto Carb (84MJ, clip in middle position)

Current max speed ~67kmh (GPS verified)

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


Tue Apr 23, 2019 9:58 pm
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