Thinking of modding my 79cc

[Professor Knowitall]

Anyone have any idea how to make it so the rockers aren’t wiggling around.

Are designed to wiggle at top dead center if you remove the wiggle your tolerances are too tight and chances are you're going to run your piston into one of your valves. Find top dead center on the Powerstroke which immediately follows when the intake valve goes from open to shut the top dead center and let it drop a tiny bit that's exactly what you want to measure valves. set intake valve lash at. 006 in. and exhaust at .008 in. when the engine is cold, a performance tune would be slightly tighter by about a thousanth in. Make sure there's a pause between 1 valve opening and the other closing. It's called overlap. I don't have the room to explain it but it's very important, eliminate it and you'll have more problems than you started with. The valve clearances are for the 79cc predator so make sure that's what you're tuning, otherwise the procedure is the same just figure out what your engine valves clearances are. Exhaust lash typically larger than intake lash.

 

[Professor Knowitall]

While my 79cc motor is on the bench I think I will modify it. It already has a better plug so I'll probably get a bigger main jet, remove governor, make the exhaust into a straight pipe and was even thinking of taking the stock valve springs from the 212 hemi and putting them in the 79cc. Upon further inspection not only was my coil going but one of the rockers was way too loose. I think I will try to limit rpm with the throttle stop and maybe get a tachometer. I could try to drill the jet but I don't know what the stock size is or what it should be drilled to. I like how the motor looked on the Micargi with the same name- predator. Also mountain bike handlebars on a stretched beach cruiser aren't comfortable I found out. Any tips or info appreciated also what top speed would I be getting in the 40's? I couldn't get the clutch off so I bought a puller. The clutch is shot I think when you spin it it hangs up and it slipped before so might have to get another one.

Be careful not to overpower your bikes engineering. If something comes apart on you at those speeds (seat post forward, back end not as critical ) could be a deadly situation. I recommend disc brakes. triple tree forks four bolt stem clamps, keeper washers on front axle anything you can do to make it less likely to rattle apart. 35mph on a bike is crazy! 40 and up, you're building a death trap unless you re-engineer pretty much every component. if you ride it night make sure you're not out running your lights. scary stuff to be guessing what's coming up. I stopped a build and downsized my power plant after I realized I had to reinvent the wheel for it to be safe. Evel Knievel? No way man! I like living.

 

[Will'smotobikes19]

Oh I won’t be using it that motor is junk even with spark, fuel in the chamber and .005 lash it wouldn’t run. My 2 stroke bike went 37 running bad but probably goes 40. The ego maniac reportedly goes 75. This was an old thread my new thread reads vintage mountain bike/3hp flathead build.

 

[Mad Willy]

Oh so true. Had a top end go on me while doing 45ish. I lived but all I can say is don't do it. Because you can doesn't mean you should. I can way out build my 'stay alive' zone, but why would ya? ..and.. these little motors arent engineered to go 45 all the time as they are. Live to ride, ride and live.

 

[Deleted member 26224]

Set your lash at a few degrees past tdc. On the 212 it is when the piston goes down 5mm after tdc. Do not use the 212 valve springs without checking that the solid height is the same as stock springs, to prevent binding at full lift. The rounded bottom nut rocker design works great. It takes some fine tuning as you must be careful tightening it up to not get a tighter lash. 5 seems like a lot, 212 spec is 3 and I used to set it by feel to .001”.

 

[Chainlube]

The measurement is probably .003-.005.

 

[youngchap]

The measurement is probably .003-.005.

okay ty i will try that i will have to go back to the store to get smaller valve gages