Open air filter installation Question

[UkeyDan]

Hi there folks! Some quick info, then the question:

I've a newly purchased Agility 50 (October 2013). The bike was derestricted prior to sale at the dealer, where they informed me that the CDI was cut, boss drive modified, and a larger jet was installed. I have since installed a no-rev CDI, hot ignition cable and iridium sp plug.
It tops out at 42mph or so, 50 downhill, averages at a steady 39mph throughout my commute. It can take a few good hills at 25-30 if I get a good start.

The bike was bought to replace my first car, which I had for 6 years. My primary commute is 10 minutes from home, so I opted for this economical alternative. I gottta say, I LOVE IT. Reliable, easy-ish to repair and maintain, cheap, and FUN! But ever since I broke it in, I noticed it gradually running more and more rich. Now its to the point that it hesitates at acceleration after startup, until the engine gets good and warm, then it runs like a top.

My thought is that since the dealer upped the jet, perhaps I should install an open air filter in place of the stock airbox. I've purchased two so far, and when trying to attach to the intake on the carb, they are too snug... My question is: Is it possible to use the airbox's flexihose as a means to extend the airtake to allow for the tight fit? How have other agility owner's fit their filters in there? Filter brand/model suggestions that I should heed?

Any help is appreciated!

[Resolve]

Becareful adding the open air filiter.  It may require you to have to up jet again to prevent leaning out.  on these scoots for safety sakes it's better to be a little rich then a little lean.  Also just because rich on take off doesn't mean you are at full throttle.  Just need to be careful.


I sometimes have the same issue you explain regarding hesitation until scooter warms up, but mine alot of times seems more temperature sensative.  When it is colder outside temp wise it happens more so than when the weather is warmer. and normally after it has sat for a few hours in the colder weather.  I normally start the scooter and let it run while I get situated (putting on gloves if colder, putting on my helmet,  etc..) then when get on I test it, if still hesitant I slowly give throttle until full throttle.  BUt after a short distance it is no issue.

[baddi]

Even on the hottest days, no rich mixture has caused any problems for me and trust me, i've tried all possible mixtures.

Anyway, if you remove the restriction in the rubber piece between the air filter and the carb intake, the stock air filter will give pressures very close to ambient and even, sometimes at around 7500-8000 rpm, a little over ambient, because it is more or less tuned in length.

The original filter are very good at filtering, both because it has the air speed going up and down and because it has such a good filter element, all while having a very little pressure drop.

With an open filter, you will have alot less pressure drop when outside the tuned rpm, but the filtering ability is also very much less. Try looking at this site, which is very well documented: http://www.max-boost.co.uk/max-boost/intake/intake.htm

BTW, the tuned length for the intake of a 50cc engine at 58cm at 3rd harmonic and 35cm at 5th harmonic. Although this changes with the temperature and pressure (smaller diameter = smaller pressure, but this is very, very little and insignificant, so count on ambient pressure or a tiny bit lower).
The lengths should be measured from valve to tube opening, which is inside the filter box.
You calculate this by calculating the speed of sound, which is dependent on the pressure and temperature, which will be in meters per second and then calculating how many seconds your intake valve is opened and then multiplying those two.

[245luigi]

Just to be clear, tuned length is from reed valve to carb attachment on airbox?

[MotoRandy123]

"But ever since I broke it in, I noticed it gradually running more and more rich."

Maybe the automatic choke thing isn't working right? It's just wax and a needle valve.
I've seen manual chokes you could add on...

[ophelia]

How do you know you are running richer and richer? Is it possible you are running too lean?

When you roll the throttle on and off before the bike has fully warmed up, do the revs slowly take time to climb and then stay high? Or does it sputter immediately?

[UkeyDan]

It sputters immediately, and it also backfires upon sudden decelerations.

[tortoise]

hesitates at acceleration after startup, until the engine gets good and warm, then it runs like a top

Ditto