My mk2 can not run at low speed.If I have to keep it at low speed because of traffic,the engine stops after about 1 minute at low speed.It's also very difficult to start the bike again.But it can stay at neutral gear and idle speed for quite long time.It only happens when I'm riding.Does any one know what the problem is ?

I'd say your running very rich. take the plug out and check the colour, it will probably be very black and oily. Because its so rich ypour fouling the plug at low speed and because it is fouled, it wont start again.
if this is the case try going a size or 2 smaller on the jets, But check your oil pump is set correctly first and this will also cause you problems.
With the engine off, remove the pump casing and twist the throttle full open. there is a mark on the casing and a mark on the movable part. these should be aligned, if not adjust the cable untill they do.
Jon

I had similar problems. I changed down 2 sizes pilot jet and went to an 8 plug grade as opposed to a 9. Has all but sorted it.

Check that your air screw is set to recommended and possibly go down one pilot jet size (I have quite a modified engine). Also check the needle is in middle position and possibly drop this one level.

gaitrinh wrote:My mk2 can not run at low speed.If I have to keep it at low speed because of traffic,the engine stops after about 1 minute at low speed.It's also very difficult to start the bike again.But it can stay at neutral gear and idle speed for quite long time.It only happens when I'm riding.Does any one know what the problem is ?

Have you been keeping up with regular maintenance, ie exhaust system ,FILTER, check float level possibly, if other measures do not cure the problem.
Regards Mike