Zuma Piston Bad... 70cc time?

[alexk243]

So my dad has a 50cc 2001 Yamaha Zuma and the piston just went out (bike is showing very low/no compression) and I am contemplating upgrading it to 70cc.

My issues are the cost though. A 50cc piston replacement cost about $30 and a 70cc piston cylinder and head is about $150. Is it worth the upgrade if I dont plan on doing any other upgrades? What will the top speed difference be?

Also would I have to purchase any other support parts (carbs, exhaust, jets, etc... ) if I plan on changing it to 70cc?

[skuttadawg]

www.enviromoto.ecrater.com/c/974005/zuma

[gregw]

If you only do a 70cc big bore kit, you won't have to do anything else, and it'll instantly give you more torque and accelerate faster (top speed won't change much though, 10%)

www.racingplanetusa.com/cylinder-malossi-sport-70cc-10mm-piston-minarelli-vertical-p-2602-1.html?cPath=4658_7178_7184&sessID=dffd5c23efa194fd31b9623042d32307

[alexk243]

Do I need to do anything with the carb at all? from my experiance with 2 strokes I would think it would need bigger jets.

[alexk243]

Also what other upgrades should I do that are minimal in cost?

[alexk243]

Does the 2001 Zuma 50cc have a verticle or horizontal engine? I am having a hard time finding which parts are compatable. Is this a Zuma II 50cc or a Zuma 50cc?

[gregw]

The 2001 Zuma has the vertical engine.
The BBK is the best bang for the buck. And depending on what you want to do with it, swapping out the primary gear with a taller (ratio) one is another good bang for the buck (you sacrifice take off speed for faster top speed). A pipe, clutch springs, torque spring, and variator is great too, but takes alot of fiddling to get it right.
From the photos that I seen of differant model Zuma's (racing planet USA/also Scootercraft), I have the Zuma II. Looks exactly like the one in my garage. 2001 Vertical.
www.mhr-usa.com/index.php?target=mopeds&mode=mopeds_search&subcats=Y&cid=0&moped_brand_id=123&moped_model_id=693
You can also call the supplier and have them double check your year Zuma for a proper fit.

[gregw]

As far as re-jetting after installing a BBK? Yes, probably, but it's gonna be close. A pipe will make you up-jet for sure, a BBK maybe.

[alexk243]

Well the scooter is for my dad, who live in a retirement area/town were the speed limits rarly reach 45 mph. He does not want to spend much money on it, but agrees since I am already reaplcing the piston that we might as well go up to 70cc

[skuttadawg]

Yep I would it would have more take off and uphill ability and not have to work as hard to hit cruising speed . You will need to upjet the carb

[alexk243]

What does it take to upjet the carb? Any idea off-hand what jet I should buy?

[alexk243]

Oh and another question. What size spark plug does this take? When I recieved it to work on it there was no spark plug in it...

[skuttadawg]

I use a hemostat to clamp off the fuel line and drain the bowl into a gas can . Then you can remove the bowl and jets are just like a screw with a hole through it a flat head screwdriver you can R&R them My scooter came with a TK carb and uses these jets www.power-barn.com/servlet/the-1344/Mikuni-VM11-fdsh-22-Large-Round/Detail

I use NGK BR8HIX which is the iridium plug

[alexk243]

So BR8H..... would work?

[skuttadawg]

Yes the 8 is cooler but a 7 may work better in the winter time since its hotter

[skuttadawg]

Here is an exploded diagram that may help you and others site.scootertronics.com/40QMBengine.pdf