Normal Break-in?

[junglepig]

So, I've been breaking in my new (and first) motorized bicycle. It now has about 15 miles on it. I'm running 16:1 conventional Super-Tech (Wal-mart) 2-stroke oil for the break-in period.

Until late today, at around 20 mph (4500 rpm) she would seem to "top out" and fall on her face at WOT, and I never pushed it. Today though, while going down a short but steep hill, gravity assisted and pushed her to 25 mph. I gave her the throttle for the hell of it, and it just sort of "came to life" and pushed on up to 30 mph as I ascended the matching hill on the other side. Since then I've opened it up a couple of more times briefly on the flats, and the dead spot is mostly gone. It still stumbles just a little at around 20, but then picks up and will go right up to 35 (about 7500 rpm).

I'm just wondering if this sounds like normal behavior as the rings wear-in and seat? Or does the flat spot in the middle of the rpm range at WOT sound indicative of a particular sort of breathing issue for the engine?

Anyone want to either explain what's going on, or speculate about it? I'm curious what to expect and what to watch out for. I'm kinda a noob to two-stroke performance issues, design, and considerations, but I'm eager to learn.

 

[crassius]

even after rings start to get a seat, it will need about a mile to warm up enough to respond well

tuning during the run-in period isn't easy as motor will slowly lean out a bit every so often until it gets all smooth & shiny on the moving parts

I'll sometimes just move the clip on the carb needle a bit during the run-in if it stumbles annoyingly, but then I have to keep an eye on spark plug in case it wants to go too lean.

 

[Tyler6357]

Engines can change quite a bit during during break in, that is why it's best to break it in before doing the final fine tuning. I would recommend that you go 24:1 for break in and 32:1 after. It's generally accepted that the Mfg recommendation of 16:1 is too much oil and will only gunk up your exhaust pipe, it doesn't need that much.

 

[junglepig]

Thanks Tyler6357 and crassius.
I'll just keep going with the break-in then. I have no previous experience riding two-strokes, and frankly, discovering the burst of power available in the upper mid-range of this thing was a little thrill for me . All my previous dirt and street bikes have been four-strokes with such a smooth power characteristic.
Until she turned-on yesterday and suddenly wanted to accelerate to 30-35+ mph, I was thinking the China Girl wasn't going to be that much fun to ride. I now think I have room to gear her down some. This bike isn't safe at those speeds anyway, and I live in a very hilly area.
I just started reading A G Bell's and Gordon Jenning's handbooks on two-strokes. I don't have the resources right now to be heavily modding anything, but I do want to understand my engine better.
I'm rambling a bit. I always do.
I checked my plug yesterday, and it looks like she's running on the lean side. Insulator is a uniform light grey color. I think I'll raise the needle one position, not for "tuning" per se, but just cuz I don't want to hurt the engine.
After I move that a little more in the right direction, I may move up to a 20:1 or 24:1 mix.
Thanks for the advice guys!

 

[crassius]

I live in an area with hills like walls - for customers over 230lb, a 44T rear sprocket will get them up any hill around here and for lighter riders, a 41T sprocket works well