FourDoor, a stock XR100 puts out a little more then 7hp at the rear wheel... the BBR kit puts an extra 2-3hp depending on what cam you use, exhaust and all that other stuff plays a small roll in it as well. I'm hoping that after I do a 6mm stroke, the Powroll cam that I'll be above 10HP at the rear. Any more then 14hp on these motors and the tranny becomes a problem... so I've heard.
The major gain in doing this swap is the amount of torque you'll get out of this motor... with a high compression piston and a stroker kit, this thing will rip!
And yeah, after I made my own mounts, I just had to cut that small part off the bottom, where the stock 50cc motor mounts to at the bottom, and it was good. About the size of a thick washer. I did end up putting a thin washer in there, just to keep things tight and not "pull" in the bottom of the frame too much when I bolt down everything nice and tight.
I've got it broken down cost wise..
$200 for 2 XR100 motors, one was a 89 the other a 02.
$250 for the BBR120 kit still in the box... got it off a friend, but they are $275 new
$200 to a friend, for some parts that I needed, head, flywheel, CDI, etc..
$35 for a EBC clutch kit
$120 for more parts from service honda... small things that I needed, gaskets, bolts, timing chain sprocket and tensioner, flywheel cover, etc...
$250 for the custom exhaust to be bent.
$45 for the exhaust can on ebay
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total is $1100.. I sold all my 2 stoke stuff and a few college school books to pay for the conversion! I've got around $100 left!