First motorized bicycle build - awesome experience!

To start off, let me say that before I got into the motorized bicycle hobby I knew nothing about mechanics and engines. I didn’t even know what the difference between a 2 stroke engine and 4 stroke engine was and what a clutch, sprocket, carburetor, crankshaft, and ignition coil were. The poor quality on these Chinagirl engines actually makes them perfect for learning; they force you to fix the issues they have and in doing so learn about engines! Hopefully I’m a little more skilled now.

This bicycle is a Trex Navigator 2.0 that was sitting unused in my garage for a couple years. I went out with a couple times this summer when the weather was nice but quickly found out that pedaling a bike is pretty boring. So, I went on eBay and ordered a motorized bicycle kit and after installing it, almost crashed into a tree at 20mph because the kill switch stopped working and the clutch wouldn’t disengage. The pictures of the bike below are the result of about two months of work.

Top speed - 33 MPH flats, 39 MPH achieved downhill. No engine porting or carb tuning

Upgrade List (completed)
Aftermarket throttle
Front Basket
Speedometer
USB Power Bank
Sparks plug (NGK Iridium B6HIX)
iPhone mount
Unrestricted muffler (sounds like motorcycle and improved torque + acceleration. I didn’t want expansion chabecause it would be crazy loud)
Dual pull brake lever
Better quality fuel line
Rubber mounting
LED Rear light
LED Headlight (custom 3D printed mount to fit basket)
Tachometer
38T sprocket
Aftermarket brake pads
Aftermarket clutch lever
Aftermarket clutch pads

 

[RB55]

Went for a ride today and decided to push the engine to the max on the downhills. I topped out 46mph @8,100 RPM according to my tachometer. It’s amazing what a small Chinese 66cc motor can make a bike into!!!

 

[Street Ryderz]

46 mph with a 38t gear on a 26" wheel is around 9,700 rpm,8,100 would be around 40mph. what type of tach are you using? A magnetic/inductive pickup type are good but can be susceptible to interference but not as bad as the ones that just wrap a pulse wire around the spark plug lead.At those rpm stock ignition and head you wanna be careful pushing it down hills that's a good way to create detonation and kill your engine quickly.

 

[CrazyDan]

I only go WOT on a downhill run when I am trying to get up to speed, once there I just rev up to get back to speed after coasting a bit if it drops (only does on uphill sections). If the speed limit is under 40 then I go to 3rd gear to keep my rpms low. I am running a shifter kit so it helps tons with keeping rpms low at high speeds. Spooling your engine at 9k rpm wears it out more than twice as fast as 4500 rpm, the forces are way more than 2x greater. If you can do the proper porting, tuned expansion chamber, proper timing, intake and header length, then you should go much faster with a lower count rear sprocket with similar if not better acceleration, better fuel economy (6k rpm fires 33% less than 9k rpm) and longer engine life (a piston moving up and down at 2/3 the speed of another will wear out much slower, along with the crank, conrod and every other moving part.

 

[RB55]

I am just using a tachometer off eBay that wraps a wire around the sparks plug wire since the inductive tachometers for cars and motorcycles require a 12v power supply which I don’t have (need to buy 12v battery!!). I know the high RPMs are bad for the engine and I only do this for a couple seconds on the downhill. I might get a real tach in though just to see the needle go up and down

 

[Chainlube]

This little tach connects through the kill wire, https://vegascarts.com/products/85mm-adjustable-tachometer-for-gx390-clone-0-8000

Says it's for clone engines but I bet it could be made to work on these bikes.