kymco agility 50cc -80cc kit

[COFFTEA]

Hi all

I am thinking about doing a 80cc big bore kit to my agility 50cc
Is there anything that would cause a issue when upgrading
like would everything be able to handle the increased pressure. 
Will a standard/stock carb be ok which is for the 50cc
Any issue that may give me a headache basically lol

many thanks

[The moped learner]

Is it derestriteed is it upgraded at all. Is it have a upgraded jet?

[tortoise]

anything that would cause a issue

Heavier pistons unbalance the rotational dynamics and enhance bearing failure.

[blue]

Not worth it . All the scoots I have seen so far. about 7 out of 10 ends up bending a crank or messing up the pistons. you maybe one of the lucky ones . a bigger scoot like a 125 or bigger is better. if you get a better crank when ya put the 80 cc in you might be better off.

[COFFTEA]

Sounds scary if I bend the crank...
best to stay 50cc then

I currently have a racing cdi which made it go 40. carb is standard so is the variator and boss.

Any ideas what jet I shud go to so its a little better top end it currently has a stock 80


many thanks

[Resolve]

Honestly, if you are not running lean the no need to up the jet.  more fuel doesn't necessarily mean more power.  If mixture is right now then you will just be wasting fuel.

I would agree that if this is your main means of transportation or you don't want the possiblity on failure then don't upgrade.  I am going to be upgrading since had other issues and this is no longer my primary mode of transportation.  I am going to use the kit that Zombie posted in my thread and claims to have had it for 2 years now. but if anything doesn happen agian not my main ride so would have chance to fix without worries.

As for the bent crank or other issues.  Yes you are pretty much reducing the life of the parts if they are not designed for bigger, but the actual longevity can be dependent on multiple things.  It may give out tomorrow it may last years.  But also depends on how you ride.  if you go all out from start to stop and constantly like that then will pontentially last less time then if you are easy on the throttle and careful with accelerations and decelarations.

IN the long run yes shorter life span than staying stock and if that worries you don't do it.  As stated go bigger scooter.  Which is why I went to a 150 for my new one.  Acceleration is perfect for me and can easily stay up with traffic at speed on city roads with speed limit at 45mph.  I cruise between 45 and 50 and that is only at about 1/2 to 3/4 throttle depending on speed.  And the cost of that versus another 50 was only a couple hundred more.

[zombie]

You guys are all close but not correct. Like Catholics.

The same bearings used in the case bosses to support the crank in a 50cc Kymco will support a 1000 hp crankshaft. Bearings are not an issue.
The fynny thing about the Kymco crankshafts is they are mild steel, cut from bar stock, and will bend but not from running. They will bend from impact or stall but not during rotation because the forces keep them balanced.

What does make these kits fail is plug, and play installations. Nothing else. Every part installed on a cheap mass produced engine must be optimized, and blueprinted to spec.
The more you know about them the less issues you will have.
Mic the bore, and piston. If they are not within -002 then get another piston or hone the bore.
End gap all the rings. .003 for top, and .--2 for all the lower.
Drill oil relief holes in the wrist pin bosses.
debur EVERYTHING.
Install the new oil pump that comes w/ the kit or order/install one.
Measure the con rod lower end side play. Use shims to close it up or open it depending on what is needed. You want .003 total or .0015 0n each side of the journal.
Adjust the valves correctly, torque the bolts correctly.
RE adjust the valves at 50-100 miles, and RE torque everything.
Change the oil BEFORE riding, and at 50-100 miles after.
Do NOT twist, and go. Break the bike in for 50-100 miles before venturing into WOT.

The "after market" kits are made by the same people that supply Kymco. The difference is Kymco guys know HOW to install parts. 1 out of 30 "modders" has some clue, and maybe 1 out of 3-400 knows more than the Kymco factory per hour guys/gals.

That is why the failure rate appears high. You can hammer a piston into the bore cause the end gap on the rings is wrong, and blame the parts all day forever. It is NEVER THE PARTS. It is Always the installer or his/her lack of understanding on how to measure, and install them.

In the past two ish years I have worked on perhaps 100 qmb 139's. It's a cheap solid engine w/ no inherent flaws in design. Actually I believe it is thew MOST produced engine on the planet. Take your time. Work diligently. Keep your tools free of sand/crap. Invest 40 Bucks in a set of veneer calipers, and use them.

There are LOADS of tutorials on you tube, as well as written all over the net on how to build these engines. If you don't know the specs you have no business installing the parts.PERIOD!

Big Bore Kit GY6 50cc to 80cc Scooter Moped 139 QMB 139QMB Cylinder Piston Rings | eBay
http://www.ebay.com/itm/Big-Bore-Kit-GY6-50cc-to-80cc-Scooter-Moped-139-QMB-139QMB-Cylinder-Piston-Rings-/221130667198?pt=Motorcycles_Parts_Accessories&hash=item337c6a34be

100cc Big Bore Kit Performance Power Pack GY6 50cc QMB139 Chinese Scooter Parts | eBay
http://www.ebay.com/itm/100cc-Big-Bore-Kit-Performance-Power-Pack-Gy6-50cc-QMB139-Chinese-Scooter-Parts-/161018753179?pt=Other_Vehicle_Parts&hash=item257d77309b&vxp=mtr

Just examples... If you botch it up get a whole new engine for under 400.00

139QMB 50cc 4 Stroke GY6 Scooter Engine Motor Auto Carb | eBay
http://www.ebay.com/itm/139QMB-50CC-4-STROKE-GY6-SCOOTER-ENGINE-MOTOR-AUTO-CARB-/330283005790?pt=Motors_ATV_Parts_Accessories&hash=item4ce666b75e&vxp=mtr

[blue]

You should be ok by leaveing stock and change the jet no biger then a 82 and cut the cdi and put in the flat drive boss you will be doing 45 or better easy.

[zombie]

100% correct!

[The moped learner]

The main problem with 50cc is wind yes wind is my worst enemy if i get 20-25 mph winds against me i lose speed like im going up hill i find myself going 25-30 mph against the wind not fun at all. i think 80cc bore kit is very good like zombie said "it's never the parts, its the installer" i learned from my mess ups

[JJJoseph]

I am thinking about doing a 80cc big bore kit to my agility 50cc
Any issue that may give me a headache basically lol

The 80cc BB kit makes a huge difference to a 50cc 4T Kymco.  It takes about a day to do the install, including fiddling with the mixture (#90 jet and remove restrictor on air intake).  Hi-speed gear set will give an additional 10mph top speed.  There's no need to worry about stressing the engine since the qmb139s are also made in 100cc size for foreign markets, so the 50cc jobs are really under-stressed rather than the other way around.

[The moped learner]

That's right the crank and bairings are almost the same for 50cc and 100cc

[COFFTEA]

Thanks all such a massive help...

I decided as my bike is running rough and piston rings are gone
I have installed a new 50cc head and valves and piston and barrell.
as the rubber in my carb is knackered I put a stock carb on.

basically I have put it completely standard other than the cdi

will sell this now as it is running very nice hitting 40mph.

I will get a agility 125cc many thanks all

[zombie]

That's right the crank and bairings are almost the same for 50cc and 100cc

They are exactly the same. One part number.

five different cylinders
four different pistons
Three different heads
three different cam shafts
two different valve diameters
two different valve lengths
but only one crank set
God bless the Chinese...

[tortoise]

They are exactly the same. One part number.

Please clarify . . GY6 50cc . . GY6 150cc