Razor MX650 Project

We have more fun on these, than we do on the gas bikes.  Don't laugh.  The razor MX650 in stock form is absolute junk.  The bars are jinky.  The seating position is way off and the suspension has no damping.  The motor is very inadequate and it is too heavy for what it has.  The good news is that it is cheap and can get your kids started riding at seven or eight years old.  This is where we started.  It was fine for those first days of him just getting used to rolling around.  It was also extremely quiet, so no problem with neighbors or

Somewhere in the first months we came across this article:


The batteries were familiar from our RC experiences and the motor upgrade was a no brainer.  We went with this combo:


In the fine print it says it will take up to 75 volts.  In RC language that equates to an 18s battery.  Each of the 18 cells in series can go from about 3.3 volts drained to 4.2 volts fully charged.  75 volts comes out to a nice 4.17 volts per cell.  We could drain down to 59.4 volts if we were brave, but that would also be an epic session.  We usually quit at 65 volts or so.  The kit bolted right in, but required a new throttle.  The stock throttle is a half grip thing that wouldn't do, so we tested several different setups.  A super cheap ebay throttle that came with hard grips molded onto the handle.  A nicer Magura throttle that was ok, but stupidly expensive and our favorite is a cheap dirt bike throttle from ebay coupled with a rotary converter.  The other thing you have to do with the new motor is change the chain and sprocket to T8F, get rid of the chain tensioner and weld the freewheel to the hub, so maybe not so bolt-in. 

Pretty funny thing...  When we got this we installed it like the stock motor and just ran it in reverse.  It was awesome because it made the difference between sliding into a corner and rolling out compare to sliding both on entry and working the apex and exit.  We started feeling some potential.  So, I was playing with it in forward and reverse and noticed it was still way faster in forward.  I fought with it briefly then simply flipped it over to chain on left, rewelded the mounts and welded the freewheel hub to the wheel, since now it wanted to unscrew. 

Somewhere around this time we also switched to a damped mountain bike shock and a damped pit bike fork with proper bars.  We also switched out the brakes to some "Zoom" MTB hydraulic brakes and rotors.  The other very important mod is to cut off the footpegs and relocate them back to the swingarm pivots.  This pulled it all together

We have a couple of acres with a mountain bike loop turned walking trail and now turned mini-motocross.  The pace of the corners matches the bikes really well...  I think a perfect lap is possible, but...  You have to chose whether to go in feet up our get a foot out.  Things are happening really fast so going back and forth with the legs takes energy that isn't sustainable.  The main noises are the chain and the scrubbing of the tires.  We also hear dirt hitting our fence.  The tires are really well balanced, so body weight placement is important.  Then it's about timing and being smooth and keeping up momentum.  Sending it deeper, but not wasting it... Geeze, it's impossible!  Then there are those smooth long deep nailed the entry and kept the throttle on all the way out.  No time to savor anything, just shut it out and focus.  Shit, he's gaining!  How's he doing it?  Not sliding.  That's how