Scrambler Issue When Hot

Hi, I'm new to the group and looking for help with my 2011 Scrambler. Took the bike out for a short run last weekend and filled up at the local Morrisons as it's pay at the pump and in todays Covid world that seemed more appealing than queuing to pay. Anyway the bike ran fine for around 20 mins then started to drop power, misfire, pop and generally struggle. Luckily I was close to home. I'm not sure if it was the fuel but I've pumped out what was in the tank and today filled up with BP's posh stuff, the bike ran fine until it got warmed up again and then the same poor running happened. Any thoughts on what could be causing or what to try to fix this? Thanks in advance for any help.

 

Thanks for all the replies, I'll check a few things out and report back .

 

So update on this problem, I replaced the air filter and took the bike for a spin , still had the same proble , after 10 mins and the engine had warned up, it startef missing, and not picking up properly. Got home ordered new spark plugs. Had a cup of tea to think things through. Had another check of the breather pipes etc and cleaned up the battery contacts . It has been pretty warm weather recently so decided to get up early and take the bike for ride in cooler weather. So this morning went out, after about 10 mins it coughed and spluttered slightly but then ran without problem for a good 30mins, I decided to try it again later today when the weather had warmed up and again no problems, so I'm happy to report that I think the problem has been solved, either by running higher octane fuel through the system, by changing the air filter or by pure good fortune!

Thanks to everyone for your help