gearing and exhaust questions

[waarblin']

hey guys i have a lucky7 pocketbike, the old engine died(43cc) and so i bought a new s'pposedly 49cc one (it says ZH-2 at the base4 of the cylinder) and fitted it to my bike using the old exhaust. My mate has a bike with the same engine and it tops out at prolly 65km/hr stock, mine is closer to 45km/hr, now his goes the same as another of our mates who has a 7 tooth front sprokcet so i'm assuming his too has a 7 tooth sprocket, i know mine has a 6 tooth front sprocket and it feels like it could go faster if the gearing were changed. BUT, and i apologise for this long assed way of writing, i've been told that stock pocket bieks come with 6 teeth front sprockets so my quesiton is basically what is holdingmy bike back????
My mates bikes both have the same stock exhaust but mine is different to theirs, is it the exhaust? Is it my front sprocket?
and i find with this new engine and full throttle i get a surging sorta sensation the bike doens't rev out cleanly at all what the hells that about? (from reading other posts i'm thinking some fuel flow thing)
anyhoo i'm an idiot with a spanner so any help would be greatly appreciated!
johnny :P

[RD RACING]

waarblin, rule number 1 please give your engine time to run-in, i hope you are doing this. the run-in mix should be 25 to 1 non synthetic oil. use atleast 4 tanks of fuel before opening up the throttle fully. then go to no more than 40 to 1 using full synthetic oil [motul 800 or simular] fit an ngkbm7a sparkplug then you can change your front engine sproket to a 7 tooth, a 68 tooth on rear should be ok. by the way change your stock fuel filter and hose with something better than the chinese rubbish.

[waarblin']

heya thanks for that i'll try that, i live in west pennant hills in sydney just wondering if you or any of the other guys know of any pocket bike shops around here where i can buy parts?
don't have a credit card so i can't use the internet.

[RD RACING]

have a look [above] at some of our sponsors, you will find what you need here waarblin. there are many ways to pay for items without the use of credit cards, ask the supplier.

[noidea]

ask your mates if you try their exhaust on your bike. My bro got a shit exhaust with his pocket bike and his bike runs really bad. When we put mine on it went alot better. Using ebay you dont need a credit card and im sure other places will accept bank deposit. The surging may be the result of the pipe aswell. Try your mates and see if all your problems go away.