Sounds like you've been there done that and got the headache....lol..I double nut everything I can....and I use leather from work gloves or belts ,old boots.....etc.to put between my engine mounts,gas tank,tensioner...anything that could slip and cause damage....it works perfect...you can dye it too..(to match the paint)....or use sharpies....I've build many MB bikes over the past 3+ years and have had lots of interesting failures occur. Here is my list (some may call it silly) of tips that I follow now before every bike build.
1. Pull head. Loctite (red or blue )or JB weld each head stud into the block. Rationale: studs vibrate loose and a MB owner may think that its the head bolts that are loose and tightens them and causes the stud which is backed out to strip which requires a fix that is out of scope for most with limited mechanical knowledge. Yes, the JB weld is extreme but I have had stripped or damaged engien block threads with loctite use on studs that I had to remove and reinstall for a rebuild or gasket leak. If you do have damaged stud mounting threads on your block and don't want to drill and retap or use a helicoil, JB weld works as long as you have residual threads in the block and use it as directed (don't use the quicker curing JB weld, the slower cure JB weld is stronger and tolerates heat better)
2. Ensure little pin on piston that prevents rings from rotating cannot be pulled out. If it can be pulled out, JB weld it in. Rationale: I had a pin fall out, causing piston ring to rotate and catch on a port causing lots of engine damage. Probably not necessary to do this but it happened to me and cost me a new complete head and the worst of it, I had to pedal. This tip is probably not necessary but something I wanted others to be aware of.
3. Use locknuts and new USA made washers (including lock washers) on the head. Do not use those "acorn" nuts on the head. In addition to new lock nuts and lock washers, JB weld (blue) the headbolts after you tighten them to the correct torque setting. If you are like me and overtighten head stud bolts, acorn nuts may damage the thread. 15 ft-lbs torque is ideal but my calibrated arm usually overtorques the head stud nuts.
4. Intake, exhaust, all engine mounting studs. Replace with US made metric all thread and cut to size. Rationale: Chinese factory studs may eventually fail and leave you stranded.
5. Nuts for intake, exhaust, all engine mounting studs. Use metric couplers with lock washers and blue locitite to mount all of these. Metric couplers have 4 times the amount of thread than a regular nut does which allows some serious torque to be applied to those US metric all thread studs. Couplers cost a 1.50 apiece but that is cheap compared to a broken engine mount or losing a muffler 20 miles from home.
6. Carb: take it apart and loctite (red) the main jet. Locktite (blue) the screws holding it together. Ensure float is properly set too (see other threads here on MB regarding this)
7. Intake gasket: throw away factory intake gasket. It will eventually blow...some sooner rather than later. Cut new one from gasket material bought from NAPA. Use gasket sealer/tack for gasket prior to install.
8. Exhaust: Heat elbow cherry red to bend it as necessary to clear pedals. Don't use engine as mounting point when bending exhaust. I use a vise.
9. Loctite blue all bolts to engine covers. Some folks and I do this occasionally: replace all cover bolts with USA bolts (I like using hex head bolts). Nothing worse than losing your clutch cover bolts and not being able to disengage clutch. Do this only after you are 100% sure clutch is properly adjusted.
10. Relube the clutch engagement pin and ball.
11. Touch of lube on gears on clutch. Rationale: less noise.
12. loctite (blue) the small screw/bolt on the clutch assembly that prevents the clutch adjustment from rotating. Rationale: it can loosen and fall out making a mess and possibly damaging the gear asssembly and/or clutch.
12a. Loctite the bolt on the small drive gear in the clutch assembly. I have had this bolt fall out before and have seen several threads about this issue.
13. Engine wiring: do not install the kill switch wire until you get engine running. Rationale: eliminate a source of potential no start condition.
14. All wiring connectors: cut and throw out stock connectors and use covered blade connectors. I solder and crimp mine and then use shrink tubing on everything along with conduit for a nice clean and professional install. Rationale: stock connectors will get loose causing wiring to come apart or intermittent connections. Any connector that comes loose with a simple tug is a no go in my book. Your opinion may vary. I have had wires pull out of stock connectors that were crimp connectors and not soldered. Heat shrinking stock connectors together may be an easier solution.
15. Lube all cables. I use lithium grease. Rationale: some cables are dry and some are frayed. Pulling cable wire out of sheath and inspecting and lubing is a good idea. If in doubt, replace cables. Rationale: lots of frayed cables and premature cable failure out there on the cheaper kits.
16. Kill switch: If it is not integrated into the throttle, don't use it and buy a replacement throttle assembly. The older style separate kill switches are JUNK and fail causing a no start condition. A quality replacement kill switch is about the same cost of an integrated throttle kill switch from Dax.
17. Chain tensioner roller: get a bearing one from Dax. Rationale: stock ones don't have bearings and don't spin freely and are worthless in my opinion. Stock one is good for the week or two you use it waiting for a Dax bearing one to come in mail. Some kits come with bearing ones now...
17a. Chain install: Always clip on your masterlink so the opened end faces toward the rear when it's at the top of the chain run and going forward.
18. Chain tension: chain will stretch by an inch or two during first 50 miles. Keep eye out and don't use bike for transpo to/from work until you do multiple test ride and shorten chain and adjust tension with roller bearing. It shouldn't be said, but you need a chain breaker for install. On a new chain, I always make chain tension fairly tight but once chain as stretched, I make sure that is about 3/4 of an inch play/slack.
19. Rear sprocket: replace all nuts and bolts and lock washers with US made ones. Rationale: The chinese bolts threads strip when you need to tighten down that donut. Use locknuts in addition to lock washers. Nuts will need frequent adjustment during first 100 miles as the donuts settle onto the sprockets and routine tightening for course of ownership. Alternative is to spend money for livefastmotors clamshell mount for rear sprocket which will save lots of install hassle, allow you not to worry about broken spokes. Ensure sprocket is mounted so it runs true. It can be done but takes a while. Have rear tire checked for balance before installing. Clamping donuts onto sprockets can cause wheel to be out of round.
20. Clutch lever and throttle assembly: if kit doesn't have a push button locking clutch lever, buy one. I also drill small holes through the clutch bracket and on the throttle assembly and install a bolt thru the handle bars to prevent throttle and clutch levers from rotating in case they loosen or lose their mounting bolts. No offense dax, but your two piece clutch levers are brittle (pot steel?) and break if you tighten them enough to prevent lever rotation. Not an issue with this tip. Also, the small washer or eclip on bottom of the locking button has fallen off on me. I now solder it into place so this doesn't happen.
21. Spark plug: throw it away and replace with an NGK or champion plug. Rationale: very common for plug to fail internally. It will always fail at the farthest point away from home requiring uphill pedaling the entire way back home. Stock plug is ok for a while but you really replace it, its cheap insurance.
21. Spark plug wire and boot: throw away and replace with an automotive plug wire and boot. Rationale: stock plug boot has a small clip that keeps it mounted to plug. It often falls out during ride causing intermittent connection to plug.
22. If you drill through frame don't use factory bolt for front engine mount install. It may shear. I always use a bolt that is larger and US made.
23. Gas tank fuel petcock. Remove it and unscrew the screen filter that is in the petcock. Rationale: Had one clog on me from rust in fuel tank.
24 Fuel line: install inline fuel filter. Rationale: needed or crud in fuel tank may clog fuel line.
25. Fuel mixing: Use empty windshield washer gallon container. Add oil to container and them fill with gas and shake. Don't add oil to fuel in take because it will settle to bottom and oil will run to your carb causing a no start situation. Windshield washer containers are compatible with gas so don't worry about it. I've been using these as gas cans for many years with no problems in leakage, venting, or safety.
26. Oil and oil ratios: The 16-20:1 ratios are unecessary in bearing engines. Run engines at 32:1 when new and 40:1 when broken in. Oil to use: I prefer Maxima 927 or Klotch Supertechniplate because it has 20% castor (not castrol) in it. If you wish, buy a gallon or quart of castor from a RC hobby store and blend it with a quality 2 stroke oil. The ultimate blend would be 1 oz of castor oil with 2-3 oz of Amsoil or other oil of your choice per gallon fuel for the ultimate in engine protection. Castor has almost twice the temperature stability than regular oils-see my other posts. NOTE: YOU MAY VOID ENGINE WARRANTY IF YOU FOLLOW THIS TIP but then again most are only 30 days and 16:1 is just too much in my opinion for bearing engines.
27. Check plug gap on that new US or Japanese sparkplug before install. Plug gap should be about 22 thousands of an inch or ball park. Some plugs gaps are completely closed out of factory and has caused me some embarrassment on a no start situation because I just screwed the plug in without even looking first.
28. Wheel bearings: repack all of them before engine kit install. (sorry, this wasn't in an earlier step). Rationale: there must be a shortage of wheel grease in China because there was only a hint of it on my bearings.
29. Bike general stuff: engine vibrates and can loosen many bolts. I have lost pedals that weren't loctited, had brake assemblies fall apart etc...etc.. Note: loctite may void your engine warranty.
30. Fuel tank: put gravel in tank before install and shake too loosen rust. Rinse and repeat as necessary. There is lots of rust and crud in many new tanks. Some folks will seal the inside of tank...a good idea. Rinse well if you use gravel to get dirt and particles out.
30a. Fuel tank studs: sand paint around studs coming out of tank. JB weld the area. Rationale: some studs leak fuel out of where studs are mounted to fuel tank.
31. Double sided tape: Put double sided tape on bottom of fuel tank. This will prevent scratching of bicycle frame, keep tank from falling off when you are using both hands to mount the frame clamps and nuts. Also allows less torque on tank studs to prevent tank from rotating around the frame. Don't forget to use locknuts and lockwashers and loctite.
31a Double sided tape: chain roller bracket. Put doublesided tape on anything that is clamped onto the bike frame. This will prevent scratching paint as you do the necessary sliding back/forward to get correct chain tension and setup. I often make a new chain as tight as possible by moving bracket as close to rear as possible. Then I use the adjustment on the BEARING roller to tighten chain as it loosens from use.
32. Loctite brake pads nuts. I have had pads loosen on me.
33. Rear sprocket, before install, it may be necessary to grind some of the chrome off of the sprocket (if sprocket is chromed) to reduce chain binding or jumping.
I hope this helps. Some tips are overkill and some have been called silly but these tips are due to failures/problems I have experienced in my MB adventure