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 YAMAHA PREBUG ZUMA - jetting help on a 70cc kit 
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Newb
Newb

Joined: Wed Jun 24, 2009 11:41 am
Posts: 6
Location: Ohio
scooters and mods: 1990 Zuma II, 370 miles, Leo Vince ZX, DIY paint job
Post YAMAHA PREBUG ZUMA - jetting help on a 70cc kit
I'm trying to figure out the main jet size for my 1990 Zuma with 70CC kit with LV ZX pipe and stock airbox and carb. The manual says stock is a #93, but for some reason mine had a #90 in it when I bought it (used) and it had problems going to WOT even when I bought it. Now I have the upgrades installed and the thing runs great except for the transition from 2/3rd or 3/4th throttle to WOT. If I back off the throttle I can coax it up into the top end, but I'd like to smooth it off. Haven't tried a plug chop yet. But plug looks OK after riding through various RPMs on a commute. I am guessing it's lean, but maybe it's actually rich since closing the throttle opening seems to help. What size is your main jet if you are running 70CC with stock box and carb?


Thu Aug 06, 2009 11:50 am
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Newb
Newb

Joined: Wed Jun 24, 2009 11:41 am
Posts: 6
Location: Ohio
scooters and mods: 1990 Zuma II, 370 miles, Leo Vince ZX, DIY paint job
Post Re: Main jet size for pre-bug with 70CC kit??
After discussions with the Dellorto importer he and I both think it's running lean, so I ordered a 98, 100, 102 and 105. When I purchased the machine (when it was a stock 50cc), it would shut down at 3/4 throttle too, but the carb was dirty and somewhat clogged, so cleaning it helped. I'm not sure how/why it had a #90 in there when stock is supposed 2b #93.


Thu Aug 06, 2009 5:06 pm
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Gold Member
Gold Member

Joined: Wed Apr 15, 2009 12:56 pm
Posts: 1007
Location: Tampa, FL
scooters and mods: 2000 yamaha zuma
Post Re: Main jet size for pre-bug with 70CC kit??
i no this is a old thread but what one are you using im using a 100 and im not sure if its to big or to small. the prebugs are a puppy to get to the spark plug so i wont look at it for another couple days

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00 ZUMA
front turn signals relocated
Pirelli SL26
LV SP3
Malossi 70cc cast iron kit
Malossi front brake pads and rear shoes
Malossi variator
Malossi delta clutch


Wed Oct 21, 2009 8:13 pm
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Newb
Newb

Joined: Sat Mar 11, 2017 1:19 pm
Posts: 10
scooters and mods: 2001 zuma, zx-r pipe restriction removed. 6g rollers, Everything else is stock for now
Post Re: Main jet size for pre-bug with 70CC kit??
My 01 is super easy to change the plug. I'm interested to see if you resolved it the wot condition .

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2001 prebug zuma, zx-r pipe restriction removed, 6g rollers. Pre-mix.


Sun Mar 12, 2017 9:40 pm
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