slow down

I am building a mini chopper for grandchildren and I want to slow it down. The project started off as a Razor electric mini chopper and a Sunl mini dirt bike. The engine came off of the dirt bike and is on the mini chopper. I have allready swapped rear drive sprockets ( going from smaller to bigger). I am guessing this thing is going about 25 to 30 mph with me on it (220lbs). I did have to put in a jack shaft to change drive sides. It is a 1 to 1 ratio as of now. I am seeing these gear reducers on the parts sites. How much would one of these reduce the speed? I would like the speed of this bike to be around 7 to 10 mph. Thanks for any help.

Welcome to the site, popper.

You should be able to gear down by the gears on the jackshaft. Just for example, let's say the engine output is on the right, and the wheel sprocket is on the left, with the jackshaft making up the difference in between. I think this is the way it goes:
-Right side, engine to jackshaft: small pinion, large sprocket.
-Left side, jackshaft to wheel: same as above.
Don't quote me on that, but I think this should help drop the speed down some.

Could you please post up a few pictures of the mini-chopper and the engine? There's another way to limit the speed that works well on pocketbike engines, but all depends on the way your carburetor is set up. A pic of the carb would help, too. You can use an image-hosting site like PhotoBucket to upload your pictures, then post the links here.

Just remember your trading speed for acceleration.
Minimoto Garage - East Coast Minimoto Speed Calculator

Just limit how far the throttle can be opened by adding alot of slack to the cable until you get the desired top speed.Eventually theyll be able to handle faster speeds and that will be an easier fix than swapping drive sprockets around again..........

Just what I was thinking.