Revving problem

[Chris sweets]

Good afternoon fellas
Bought a bike which I now know was from a dodgy dealer, started having issues with it after about a month
The issue is the reviving, when the bike is started it idles fine, when your on the throttle the revs can jump all over the place even when you are holding the throttle steady, there is some popping from the exhaust when this happens
Anyone got any ideas or know of any common faults this could be?
I have searched on the internet and I'm going to start it up in the dark tonight and check from any sparking/arching, I'm also going to spray a mistake over the engine when it's on file to see if the revs change if it's taking in water from somewhere
Any help is appreciated

[longandlow]

Sounds like it could be a carb issue if it run ok on choke. Have the carbs been stripped and cleaned?

[8541Hawk]

It also could be the diaphragm in the petcock has failed