I've been breaking in my 1st motorized bicycle build and as I have done in past auto or motorcycle project I do a basic break down just to make sure no major issues. So this is what I found.
1) I noticed a little blow by on the fins around the head. I came to the conclusion that the studs were a tad long and the accorn nuts were bottoming out. (would have liked to check compression before and after, But I no longer own the tools for this. Which is why I love motorbikes, No need for a Snap on tool box and $4000 in tools) (Fix) trimmed the studs down 1/8th of an inch.
2) Took off the carb, found that the the carb did not slide all the way back on intake. creating a leak in the slots under the retaining band. (Fix) used dremel to sand away burr on the mating surface. Make sure to block opening to venturi and float bowl.
3) Removed intake, found gasket damp and stained suggesting a leak. noticed that the nut and washers were not able to sit even on the intake due to large sloppy welds. (probably wouldn't affect performance but looked unprofessional if nothing else) also decided that those studs also were too long to allow accorn nuts to properly tighten. (fix) Trimmed down studs and grind welds making sure not to get too close to base of intake.
4) Intake needed porting and polishing really bad! (Fix) give her what she needs! Used dremel to remove slag and burrs from inside of intake. Polished using 300 grit wheel.
5) Found replacement gasket did not match intake. (Fix) Mated gasket to intake and sanded gasket even using dremel.
6) Compared sanded gasket to intake port, Found rectangler intake port looked good but blocked part of the opening of the gasket (intake). (fix) Block the intake port mate gasket up, used dremel to taper back the extra material on the intake port. Clean port using rag damp with alcohol then with a magnet.
7) Exhaust gasket did not mate up. (Fix) Sand gasket even using dremel.
After what I found just from a basic tear down I am seriously considering a complete tear down. I must say the clutch appeared good as did the magneto. Before the fixxes with a 41 tooth sprocket I was running just shy of 27mph (according to my garmin GPS) after I ran a good 35mph. I would like to say that none of these issues are anything that I would consider inapproperate based on the price of these kits. I am a machine operator for a company that produces brake calipers and if these kits were manufactored to the level needed they would be double if not more in price, And lets face it we love working on our bikes! If these kits were super high quality there wouldn't be anything for us to fix or improve. What fun would it be if you threw together these things in 2hrs then never had to touch them again. I do think that next time I will also do a pre-tear down. Let me know what you have found as a result of you working on these fun little machines.
God Speed, Mark