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Sounds like an internal fault in the gauge. If it's a Chinese bike it's not uncommon. Gauges are subjected to considerable vibration and a lot of them are not very well made. An electronics expert should be able to examine the internal printed circuit for dry solder joints and dislodged components.
The input signal comes either from the pulser coil or the exciter coil connections in the CDI.
Do you think its a good idea to take out the shaft and flywheel and balance it,some people say that this cures the famous "chinese bikes vibration".Do you think its true?
The cranks are already balanced statically by the maker. It would be better if they were balanced dynamically but this would be very expensive and would require qualified operators to carry this out, so makers don't do it.
A race shop or similar skilled technician could reduce the vibrations considerably using the dynamic method but there would always be quite a bit of residual vibration due to what they call poor primary balance of a single cylinder engine, due to all those masses of piston and conrod being flung up and down at great speeds.
I've found that mine has become smoother after break-in and a lot of the vibes have been cured or at least disguised so as not to numb my hands, by weights on the end of the handlebars and paying attention to the engine mounting bolts. They were undone slightly, the engine allowed to relax and sit down properly on its mountings and then tightened to the correct torque.
Some people improve on this by fitting larger bolts, so that they fit the mounting points on the chasis and engine castings better. Some makers have oversized holes there to ease assembly by making things easier to align. The tighter the fit of the bolts the better the chasis can absorb the vibrations the engine produces.
There's a good Article on engine balance in Wikipedia.
Do you think its possible to increase horsepower in chinese bikes? More compression,larger carb,some special CDI,?
I wonder why chinese are typically 15hp and european(ktm) or japanese(yamaha) are 45hp the same cc?
Do they use better castings?
Don't really know. No-one seems to have really tried apart from basic mods which might add a couple of hp.
The Chinese use old Jap designs, but you'll notice that they limit the revs to a lot less than the Japanese engines they've cloned. Pitbike or Monkeybike engines are a case in point: The old Honda Cub 50 cc engines could rev to nearly 10k rpm, whereas the Chinese limit them to as low as 7500 on some versions. They seem to concentrate on longevity (although I've never heard of a Chinese engine doing great mileages before blowing up...!), and a low fuel consumption.
An example in my own Qingqi QM200 compared with the Suzuki DR200 is that the latter revs 500 rpm higher, has same type of carb, but 3 mm larger and I don't know about the camshaft timing, but the power output is nearly 5hp higher than mine. In my case It can't be made of inferior metals or poorly hardened parts, as the engines are made in the same factory...
oh I see
I’ve tried to take out the water in the carburetor reservoir but the screw that is intended for that it’s really impossible to loosen it, I tried with both Philips and normal screwdrivers but the head of the screw is getting worn. Any idea how can I take this screw out? May I heat it? Is it a normal screw or is it like those that look that a needle at the end?
It’s a mikuni carb.
I think the carburetor is made of some sort of alloy,aluminium or something similar,its grey.
Carbs are made of a high zinc alloy for ease of casting, as they have very complex passages and intricate detail.
The screw for carb float chamber drainage has a sort of pointed end to act as a tap, but it's not as delicate as the idle mixture screw. Support the carb from the other side so that you can "lean" on the carb with a good fitting flat screwdriver in preference to the cross pointed one. You could try with a right-angled driver like these, as you can apply more torque.
Heating might help, but being so close to flammable materials you'll need a very fine and controllable flame or even a large soldering iron with a fine tip.
http://www.elexp.com/tools/06011PK202B-C.jpg
Today I found a place where they dinamically balance with a stroboscopic light the shaft,but they told me I have to send the shaft unnassembled and thats something only a shop could do,due to the complex of job.Is this true?
Why do I have to dissasembly the shaft,flywheel,clutch?