Quote Originally Posted by Chi town View Post
Thanks Axa,
Yup, I had scoop facing the wind direction.
Will experiment the stock filter and the scoop again in the future

So, it's normal for the sputtering at top speed. That sucks.... So I guess my top speed is 55mph, sucks even more
Yes, though I said sputter is common not normal, by no means should you accept it. It can be eliminated tuning your airflow, I know that for a fact.
For me it meant top rpm from 6.5k to 7, with allowed a few mph increase on top end in the most optimal conditions. For me that is a very worthy modification.
I haven't even touched my jets or needle yet.
I will when i find a proper air scoop Ill try bumping the main jet way up, but I'm not expecting much if any improvement on the top end from it.

I saw that scoop you bought off ebay sometime ago, but speculated it was too aggressive as it has a very concaved intake. You seem to have confirmed that.
I am looking for one with a wider area but no concavity, or even some convexity.
I may need to fabricate something when time allows, cuz i am not finding what i want.

So that's why i feel the most important mods you can make to improve the top end is lowering your sprocket ratio, and eliminating any sputter.
Ultimately, this bike's top speed will largely depend on its lack of power because of drag.
And at highway speed the resistance apparently increases by an exponent. Here is an interesting read about it click to see the full article:
At low to moderate speeds, during stop and go driving for instance or while you're motoring around town the affect of drag is negligible, don't confuse this to mean non-existent, any serious bicycle racer can tell you it isn't, but as far as motor vehicles go, as long as we stay under about 50 mph it accounts for only about 5% of a vehicles total resistance to movement. Unfortunately once we reach highway speeds, roughly 60% percent of a vehicle's energy is required just to defeat air resistance, and that grows exponentially as speed, and with it air velocity, increases. If you've ever fought a stiff headwind you know exactly what I'm talking about. Riding into the wind you have to twist the throttle up like an alarm clock spring just to maintain headway. With the wind at your back, you can reach the same speed on half the throttle. Think of drag as a never ending headwind, and you won't be far off the mark.