bike is way slow, any ideas?

[newbybikelover]

ok, so, i have built my second engine on a bike, the first one was with a friend on his bike, everything went fine except the carborator filter kept falling off. i built my bike on my own with a little hole drilling help from my girls dad. And my bike is solid no problems at all, everything is very sturdy with a perfect fit. They are both the same engine, a grubee skyhawk GT5 2011, my friends bike is pulling at least 30 mph and faster passing all the trafic (he does have a speedometor), the advertised speed is 30 mph. My bike is only pulling at LEAST 20, working its way up slowly once it reaches 15, any ideas what i did wrong? my own thought would be that i probably over oiled it (which i did at first) but will that effect it that much?

 

[Bikeguy Joe]

Well, what is "over oiled"? 40:1 is a good mix, then see how fast it goes.

Also, 20-30 mph is the average speed of these things.
35mph? Maybe....25mph. Yep, all day long.

 

[2door]

One big difference might be that your friend's bike engine is broken in and yours is not. These little engines run better and better the more miles they accrue.

Also are the rear sprockets the same size (tooth count). Rider weight? Tire size?
There are many variables to consider when comparing performance. In addition it is a known fact that some engines just simply run better, produce more power, than others. Maybe your friend got a good one.

Tom

 

[tooljunkie]

i put a tach on my grubee,48cc.tops out at 6300 rpm's.i read somewhere 7000 is the peak rpm for these engines.
if you could get your hands on a tach and compare the two,you may at least have an idea what you are revving.
youtube has a great video about four-stroking,the demonstration clarifys things.
http://www.youtube.com/watch?v=0wzph3hL6EE