The 4 stroke Engine only weighs 12lbs. That is with out the gear box PTO. When you add that, it is only a few pounds more than the 2 stroke. The Total kit 2 stroke is around 20-25 pounds depending on the size motor. The 4 Stroke Titan is a little over 30 pounds complete. So the 4 stroke kit does weigh more. But not a whole lot. Since it is being placed on a bicycle, it is not that big a deal. We are developing a Titan In Frame version called the Titan IF. I hope to have that ready by Spring 2010. As for now, the Focus has been the Titan XC Rear mount. With the Titan XC R3 now being released, most will find the quality, ease of maintenance as well as reliability is well worth the extra few pounds. When it comes to rear mounts, there is nothing better than the Titan XC. And it is half the cost of any other 50cc Full size setup. Actual Displacement is around 48cc. The Titan 4 Stroke is CARB Phase II compliant. The 2 stroke does put out more emissions, but still, the 2 strokes are clean burners. They will easily pass any emissions test with 20:1 mix. People do not realize that these new 2 stroke oils are biodegradable. That is why a higher mix is needed these days and burns cleaner. Just because the 4 strokes are cleaner, does not mean the 2 strokes are polluters. There are emissions with everything you do. Do not let the 2 strokes get a bad rap. 2 Strokes are awesome !!! 4 strokes are awesome too !!! Anything that gets 110-160 mpg is as low a foot print as it comes. Enjoy the ride...