dt125 problem, not starting, cutting out?

[KTM21]

I went to ride my bike today and it was harder than normal to start, but it started eventually. So I started riding and it didn't seem right, it sounded very low pitched and wouldn't rev past 5k. So I stopped and had a look at it and it just cut out. From then on it was extremely hard to start and would always cut out after about 10 seconds. So I removed the spark plug to have a look at it and it was very oily and the oil was a dark colour. I cleaned the spark plug and then put it back in the bike and it ran like normal for about 2 minutes and then returned to the same problems as before. I didn't have another look at the plug but I am pretty sure that it would be covered with the dark oil again. I am very new to bikes so I am not sure what the problem is. Any advice?

[eastanglianbiker]

do you know when the air filter was last cleaned/replaced as that is the first thing to check

[KTM21]

do you know when the air filter was last cleaned/replaced as that is the first thing to check

 

I bought the bike about a month ago and I haven't replaced it since so I don't know when.

[TomGrainger]

Check the voltage on your battery and change your spark plug. I had a very similar thing happen on my DT and a replace of the above was all it needed.

[KTM21]

okay, the battery needed replacing anyway.

[acting_strange]

Could be a sticking/stuck choke....

[Joeman]

Blocked air filter and warmer weather may be causing it to run rich.

Also what oil are you using? The cheaper 2-stroke oil is nasty stuff.

[KTM21]

Blocked air filter and warmer weather may be causing it to run rich.

Also what oil are you using? The cheaper 2-stroke oil is nasty stuff.

I have been using fuchs silkolene comp 2 oil.