49cc Mini moto engine build so far

Hello, this is my first build, it is a bit of a mess at the moment and obviously has some issues but I have high hopes for it's completion! Links to photos below as I'm having trouble with uploading to this site

http://farm6.staticflickr.com/5517/9797492404_4df4d6612d_o.jpg

http://farm4.staticflickr.com/3687/9797505766_a36bcb7dee_o.jpg

Schwalbe big apple tyres
Big Dutch made handlebars
The seat extension is a bar end from a mountain bike
Brooks sofa saddle
Cheap Chinese 49cc mini moto engine (huasheng?)
Automatic gearbox
Gokart exhaust, modified and fitted with 22mm brass pressure fitting (I actually quite like the way it looks, sort of steampunk)
43 tooth rear sprocket bolted on with galvanized steel, plywood and motorcycle innertube
Basic mini moto petrol tank, to be replaced with by a fancy board track style tank when I have the tools


As you can probably see from the photos, I have had a few problems in my test runs!
The engine shakes way too much on the mounting and is shaking everything to bits.

The mounting is made from 1mm galvanized steel which I think is too thin at the moment. I have decided to either add another mounting bracket or two, or abandon it until I can make some thick stainless steel tabs and weld them onto the frame.

As you can see the pull start is dangling because the recoil has popped out for the sixth time! Not sure what I can do to resolve this other than buy a new one unless anyone has a suggestion for fixing it?

Also, I think there may an issue between the rear sprocket and the gear ratios in the gear box because I don't seem to be getting as much power as I should. Maybe the automatic gears are not changing because there isn't enough pull due to the high number of teeth on the rear sprocket?

49ccmotorbicycle1.jpg
 
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do you have yours hooked up to the front chainring? i was thinking about using the 5:1 trans and run a 10t to the 48t on my chainring. just wondering what the cheapest way to get the cranks to freewheel?
 
Hey, thanks for the response. I was actually looking at the 4-1 gearbox the other day! I may have to get one. The setup I have is T8F so it won't be a problem changing. Are you sure the one I have is 2.19:1 though? I've found the gearbox I have in a few places but none of them give the ratio, the person I bought it from doesn't seem to know either, all they said was that it should work with the sprocket I have for top end power. I'll test it again today and see how it goes. The 4-1 seems like the best option though, thanks again!
 
one easy way to find out is to remove the case and count how many teeth are on each sprocket inside. how many teeth are on your drive sprocket?
 
There seem to be 10 on the drive and 30 on the second sprocket in the gearbox, the teeth and chain are smaller though. The front sprocket, outside the gearbox, has 12 teeth.

I don't know about freewheeling but I think you can get freewheel sprockets to fit onto the drive.
 
that means you need a 74tooth sprocket on the back. the mini moto sprockets come in that size but only have 3 bolt holes so you would have to drill more.
 
There seem to be 10 on the drive and 30 on the second sprocket in the gearbox, the teeth and chain are smaller though. The front sprocket, outside the gearbox, has 12 teeth.

I don't know about freewheeling but I think you can get freewheel sprockets to fit onto the drive.

I've never seen or heard of a T8F 12 tooth sprocket. There are tons of 11t sprockets available online for use with 6-spline shaft.
Is your 12t sprocket 6-spline, round shaft or "D" shaft?

Left-hand freewheel mechanism will screw onto a special hub from staton-inc.com or bicycleengines.com

Your gearbox is 3:1, if you have 10t/30t gears. Smaller internal drive must be #25 gears and chain.

A 63 tooth rear sprocket with your 12t gear finalizes to 15.75:1.

A 63t w/11t gear = 17.18:1

A 72t w/12t = 18:1.

A 72t w/11t = 19.64:1.
 
The front 12t sprocket is 6-spline. I just found a 10t on ebay!

I tried riding my bike again yesterday (before the pullstart broke again!) and it is definitely underpowered so I think I will go for a 54t rear sprocket and the 4:1 gearbox you suggested, which should give me exactly 18:1 if my workings out are correct and if that still isn't good enough I'll get a 10t for the front.
 
I've never seen or heard of a T8F 12 tooth sprocket. There are tons of 11t sprockets available online for use with 6-spline shaft.
Is your 12t sprocket 6-spline, round shaft or "D" shaft?

Left-hand freewheel mechanism will screw onto a special hub from staton-inc.com or bicycleengines.com

Your gearbox is 3:1, if you have 10t/30t gears. Smaller internal drive must be #25 gears and chain.

A 63 tooth rear sprocket with your 12t gear finalizes to 15.75:1.

A 63t w/11t gear = 17.18:1

A 72t w/12t = 18:1.

A 72t w/11t = 19.64:1.
8mm chain and sprockets are used Why would they use ASE when everything else is metric???
all these boxes are JUNK as there is no way to adjust chain tension as the chain stretches and sprockets wear.
 
8mm chain and sprockets are used Why would they use ASE when everything else is metric???
all these boxes are JUNK as there is no way to adjust chain tension as the chain stretches and sprockets wear.

What is ASE? I know for a fact that right-side 4-bolt freewheels will bolt onto T8F 63t and 72t sprockets.
Those same sprockets can easily be drilled to accept 5-bolt freewheels.

It should be possible to fabricate a simple chain tensioner to take up the slack in the gearbox.
 
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