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 YAMAHA ZUMA - lost my torque on my zuma need help 
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Post YAMAHA ZUMA - lost my torque on my zuma need help
Hi, I am in trouble with my baby beast: Yamaha Zuma (BWS) 2009.
It's a 2009 but all reverted to early model. 2003 muffler, carb restriction removed, antipolution removed.
It has a 70 CC Polini and the rest is stock parts.

This is what happened. I changed the V belt because it broke. Some of the variator ventilation blades wheel broke but I didn't pay attention.

Everything was fine with the scooter. 2 days after, I climbed a hill with a friend in the back and I suddenly loss torque and the motor was coughing when submitted to effort.
Coughing a bit like when your cylinder has hard dirt in the exhaust port (after putting cheap oil)

I re-opened the trans case and changed the damaged the variator vent wheel with a new one.
It didn't fixed it;
I re-opened the trans case and removed all part and air pressure cleaned everything, variator and cluth.
Still the same thing.
When the scooter is on its stand, I can rinse the motor at very high revs with no problems, nothing wrong there.

When I sit on it and try to accelerate it's as if the motor was coughing, buggy, no torque, won't reach top speed and anyway it's scary to even try.

I am totally lost in terms of what to replace or what could be wrong.

Thank you for anyone here that can help me! I do the mechanics myself on it.


Sun May 27, 2018 10:19 am
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Post Re: Sudden loss of torque BWS 2009 PLEASE HELP
Start with a compression check then a leak down test.
You ran with an out of balance situation you may have blown the crank seal

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Sun May 27, 2018 5:09 pm
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Post Re: Sudden loss of torque BWS 2009 PLEASE HELP
jmkjr72 wrote:
Start with a compression check then a leak down test.
You ran with an out of balance situation you may have blown the crank seal


That makes a lot of sense! Thanks a lot!


Tue May 29, 2018 4:25 am
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Post Re: Sudden loss of torque BWS 2009 PLEASE HELP
jmkjr72 wrote:
Start with a compression check then a leak down test.
You ran with an out of balance situation you may have blown the crank seal


I ran the motor with the variator removed. I heard rattling noise for the crankcases, like something shaky, vibrating metal parts so I am 95% sure that my seal is broken.

What do you think?


Tue May 29, 2018 12:37 pm
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Post Re: YAMAHA ZUMA - lost my torque on my zuma need help
I changed the right side seal, I still have the same problem. Next week-end I will do the left side (magneto side) seal and see if I can fix this problem. Summer is passing by and I am wasting time and money on this bike.


Sun Jun 03, 2018 3:54 pm
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Post Re: YAMAHA ZUMA - lost my torque on my zuma need help
Ok this is how stupid I am, after changing the right side crankshaft seal it didn't work as I mentioned before.

Instead of changing the left side seal because I didn't have a flywheel puller, I changed everything.

I bought a polini kit

https://www.scootertuning.ca/en/engine- ... -70cc.html

which is:

Engine Package Polini Sport 70cc (Bws/Zuma)
Model: P-PL001
Complete engine package for Yamaha Bws 2002-2011. Package include Polini Sport 70cc cylinder kit, Variator Polini Hi-Speed, Exhaust Polini Speed, Main jet set Stage6 80-102 6mm, Spark plug BR9ES, Polini 16x13 roller and Polini torque spring (Soft).

I installed everything and still had the same problem.

I finally changed the left side crankshaft seal and it was it! As a matter a fact you could tell the seal was destroyed.

Now the scooter goes OK at high revs but at low revs no power and it even stalls!

I installed the 86 main jet
I removed the exhaust restriction washer at the entrance of the pipe and drill through the exist hole of the pipe because it was also obstructed.

My Zuma 2009 engages right away at low rev, when I give it gas and has no tork, it's tough to do 0-10 mph after that it seems to be fine .I didn't go full speed yet as I have a new motor and I am stuck with the rodage crap.

I tried the move the carb needle up but I think we can't on a 2009 so I started fooling out with the a/f screw of the carb but I have no clue what I am doing.

Help me! What should I do, I want tork! The motor has amazing compression, it's even hard to crankstart it!
It sounds like a Harley Davidson now.

Should I change the carb? How to adjust that carb! Should I change the main jet down to 84? Or go to 88? I have an oversized air box too.

Help!


Sat Aug 04, 2018 5:42 pm
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