Air filter old or new slows top speed when on the Scooter

[safesinger]

As the title says weather the air filter is new or not it tops out at 39mph.
If I remove the air filter all together the scooter then gets it's normal top speed of 45-47mph.

Strange I replaced the original one I got with the scooter and it improved the speed average 45-47. That one I used for 2 years replaced with a non-Honda air filter and it wouldn't get past 35mph.
Then replaced that with a genuine Honda air filter for the 97 Honda Elite CH80/80. And it gained 1mph more than the non-Honda air filter.

So I figured belt & rollers so I replaced both I put in 10g roller weights.
Purchased the Honda belt made for it.

With little improvement besides scooter sounding better.
What could be wrong? Air/fuel?
I did notice when I replaced the spark plug it had some black on it which indicates it's running rich.
Any help appreciated.

[Wheelman-111]

Greetings:

Filters are made of some sort of plastic foam. I'm guessing polyurethane. As time passes, the "holes" in the material contract and the filter becomes more restrictive. This occurs even on the shelf of the parts warehouse. Eventually they go brittle and chunks break off.

Anyway, Get the one from NoiseGuy. It's lower-density foam, and less restrictive than the Stamped-in-1994 foam ones from Honda and the aftermarket. Yes you're correct that it's running rich if adding intake restriction (air filter) makes it worse. You'll have to pull the carb to check the number on the main jet. You didn't mention what model, year, or make of scooter for that matter, but whatever size the jet is, go a step smaller and test. Consider a temp gauge if you reduce main jet size and watch out if temps climb quickly toward 400.

[safesinger]

I did. But it's a 1997 Honda Elite CH80 80.

Should have put the specs up 1st instead of mid sentence.

[Wheelman-111]

Greetings:

Speed-"reading" has its drawbacks, sorry. Curious that the original filter performs so differently from the Non-Honda as well as the Honda replacements.

Clearly the engine seems to "like" the leaner condition, suggesting that the main is too big with the new filter(s). Was the slowdown immediate when the filter was replaced? Or was it gradual? Do you see a return to previous top speeds just pulling out the element or removing the airbox entirely? In the former case, the filter elements may have greater airflow resistance than the original you replaced. In the latter the airbox inlet holes are too small for the engine's demand. Both will richen mixture. Going TOO lean will cause excessive heat, and can even damage exhaust valve seat.

Depending on mileage, consider checking compression. A valve clearance check might be a good idea, too. These engines can go forever but the valves need to be adjusted as they can get tight pretty quickly. Coincidence with the work you performed may need to be considered.