I just shipped a 2-stroke shifter bike 1100 miles to Texas and was making re-assembly instructions and when I finished the handlebar portion I thought I'd make a topic about how I do them for reference.
Be it a direct drive or a shifter 2-stroke motorized build, if your bike has derailleur gears it also has brake levers and at least one gear changer but usually 2.
That is already 2 two lever controls and 2 forms of shift controls on your handlebars be that 2 twisters or 4 more levers, usually thumb levers.
In many cases the shifters are a part of the brake assembly.
That is a really bad combination that needs to go regardless in my book so look at that when choosing a bike.
A 2-stroke kit comes with another lever and a full grip length twist throttle control.
We have all seen the nightmare handlebars of builders that simply add a kits controls on to the handlebars that not only look scary but down right dangerous.
I have a pretty simple formula I use on all my geared bicycle builds to share and it starts with stripping everything off the handlebars and rebuilding it like this.
The first thing to go for me are the bikes grips, a box cutter is dandy for this if they don't come off easy.
Next is any front sprocket derailleur mech and control, if you REALLY need to change to a different front pedal sprocket it is easy to do by hand and one shift control is gone from the handlebars not to mention more motor mount area.
For the brakes you usually have 2 levers but you need to add a clutch so I remove both brake levers and put a SBP 'teeter-totter' self adjusting brake lever on the right with both brake cables, front brake in front, and then the throttle.
I don't use any kits stock hard plastic grips so I pull the throttle barrel out of the throttle assembly and use a box cutter to remove the crap grip.
The BMX style foam grips I use come in a variety of packages but usually have enough for 3 bikes and I use them because with a little warm soapy water you can 'milk' the foam grip over the oversize throttle barrel.
For me this one simple thing that takes the stress and vibration out my hands is worth 10x their $12 price.
For the left controls there is the clutch and rear gear shift control.
Regardless of the gearing type I use a half length rotary shifter even if that means buying a new one ($8), sure the numbers are upside down but it doesn't matter, it is one half grip twister, you can reach the clutch fine, and the rest of the left handlebar gets a foam grip cut to size as well.
I hope this helps those of you just starting, and it sure it adds $30 or more to the build cost depending on what you have, this setup is about as safe to operate and comfortable way to ride and control you machine as I have found yet and if you think about isn't that what you want anyway?