Big bore

[Jayman77]

Has anyone put a 50mm big bore on a taotao thunder with a gy6 I will be doing it in the next few days just looking for someone that has if I run into any problems:thanks:

[tortoise]

Research resource (http://49ccscoot.proboards.com/board/6/4-stroke-performance) . . enhanced odds of bearing failure.

If this style muffler (https://taotaopartsdirect.myshopify.com/collections/thunder-50/products/50cc-exhaust). . only remove top ear bolt, then pivot on loose bottom ear bolt, after removing 2 bottom head exhaust pipe nuts. Suspend muffler from upper frame with a cord. During assembly, install top and bottom cooling shrouds prior to muffler attachment.

[Jayman77]

I put in the 80 cc kit runs great but hard to get started and idle is bad and it is needing more gas I have put a cone filter on as well but still have stock muffler and suggestions

[tortoise]

put in the 80 cc kit
Pilot and main jet sizes?

If using the stock head which has around a 5cc combustion chamber . . .
39mm bore (50cc) = around 10:1 static compression ratio
44mm bore (63cc) = around 12.6 static compression ratio . . resource (http://www.ebay.com/sch/i.html?_odkw=Glixal+ATMT1-005&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XGlixal+%2 2ATMT1-005%22.TRS0&_nkw=Glixal+%22ATMT1-005%22&_sacat=0)
47mm bore (72cc) = around 14.4:1 static compression ratio . . resource (http://itistheride.boards.net/thread/9900/80cc-big-bore-kits-shipped?page=1&scrollTo=121076)
50mm bore (81cc) = around 16.2:1 static compression ratio
52mm bore (88cc) = around 17.6:1 static compression ratio

For comparison . . .
Sym 50 (http://www.lancepowersports.com/models/pch50_specs.html) 11.8:1
Honda Ruckus 50 (http://powersports.honda.com/2017/ruckus/specifications.aspx#SIbk3B1F9y3TQ2ic.97) 11.9:1
Yamaha Vino 50 (https://www.yamahamotorsports.com/vino/models/vino-classic) 12:1

Static Vs. Dynamic Compression Ratio (http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.html)

1 teaspoon (4.9 cc's) in a stock 139QMB cylinder head . . .

http://i.imgur.com/K3H7Dze.jpg

http://i.imgur.com/AC6VKpJ.jpg