I put the wrong oil in my motorbike

When reassembling the forks on a motorbike the main spring and all other internal components should be in the fork tubes then add the oil, as to weight I assume you mean fork oil viscosity. Fork oil for general use is usually 5w or 10w but you need to look up the specific oil type for your bike, also the capacity is unique to each bike but you can measure the oil by pouring the required amount into the upright tubes make sure that the levels are the same, use a straightened wire coat hanger and measure the level in each fork so that any differences are reduced so as to not affect the safe handling of the motorbike as uneven forks can be very dangerous.
Look on youtube to find videos of fork oil change etc.

Are you using the choke? Carb pilot circuit is dirty, clean the carbs.

For any 2 stoke motocross bike you can get specific two stroke gear oils from bike shop or simular just make sure it is motor bike specific as your clutch depends on it... as for brand and weights not so important just change regularly and use motorbike specific two stroke gear oil and will be just fine. I always use Bellray oils but its just personal preference and my local bike shop just happens to stock bellray products cheers mate

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Nice bike!
The gearbox may be save-able if it hasn't done too many miles with no oil.
I would use a good quality semi-synthetic 10-40 multigrade but for acurate description of your bike, check this web site out. It may help you out.
http://www.bikez.com/motorcycles/sachs_roadster_125_v2_2002.php

Safe riding.

BOth sides of crank case gets oil in em its normal for the skyjet engine
To change oil Locate the 17MM bolt under the engine near the front of engine, Unscrew and Let the oil drain for about 1 hour
Then Put bolt back and tighten properly, Then Add approx 1.6L of 4 stroke Motorbike oil

you have to take the forks out im afraid. put the bike on a few blocks so you have good height to slide the forks out, take the front wheel off and mudguard. then undo the pinch bolts by the handle bars then twist the forks left and right until they slide downwards and out. then you undo the tops and tip the old oil out. If your going to do all this you may aswell change the fork seals aswell if they havnt been done for a while. Easiest thing to do is get the forks out and then take them to a bike shop and let them do it, saves you loads on labour.
steve

Yes this is evident in replacing engine oil to motorcycle engine.

Engine oil designed for automobiles isnt good for motorbikes as they offer additives for added "slipping". THis will cause your clutch to slip. Automobile Engine's oil system is separate from the clutch while motorcycle's clutch and engine fall under one oil system.

Use engine oil designed for motorcycles.
Solution: Buy and Engine flush, pour it to your crankshaft, run the engine for 5 minutes (idle) then drain. Replace with new motorcycle oil.
-levibit-

Your oil pan where you normally drain the oil when changing it IS the crankcase. I would also drain any gas from the fuel tank(s) and put fresh gas in it, and you will probably need a new battery.

Hi. I would only use a good motorbike chain lube for your motorbike as a bicycle chain oil may well be to thin and will increase chain ware. As for oil, check in your service book or manual. If you do not have one ask at you local motorbike shop and they will tell you whitch oil you nead. Regards Tony.