speedometer

Is there a way to fix the interference the speedo will go from 21 to 98 to 3 km/h randomly.

Though I would rather an analog dial type speedometer the cables & wheel hardware don't last on my 1985 Fat City Cycles mountain bike with mag wheels & 66cc 2 stroke HT Engine from Bicycle Motor Works. I purchased this digital cycle computer from eBay for $10 including shipping. Seller is no...

So I have a phone mount on my gas tank because I use my phone for the gps speedometer app. The app eats your battery like no other so I was thinking, if you strip the end of a micro USB cord, could I wire it to the white output wire from the engine to charge my phone while I ride?dance1lo

This is most likely "old hat" for most as smart phones & tablets aren't anything new, but I figured I'd ask, to see what apps & devices others have, like & use - so please do post what you prefer (pics and/or links are greatly appreciated ofc). The following is obv an android... iphone/other is...