After travelling with my faithful steed (DRZ 400 SM) from London, through Europe, central Asia, India and Nepal, I'm on my return journey and have run into some carb issues whilst in Iran.

The issues started with some dirty fuel purchased in Pakistan, this crippled the bike - losing power sporadically at medium rpms. After limping over the Iran border, I cleaned the filter in the petcock and the one on the float valve seat in the carb; finding a ton of crap.

She seemed to be running nicely for a few thousand kms until a related problem developed, at high rpms she consistently began to misfire meaning I could only do 93kmph max to avoid any issues.

I removed the carb again and inspected the plug. The plug was pretty black and I assumed that she was running rich. So, I reset the pilot mixture screw to what I thought was the factory setting - 3.5 turns. But, I think I made a mistake with this - I undid the screw and then turned it in 3.5 turns. Rode around town with this but the problem persisted - when I removed the plug later it was completely black.

So, I corrected this - turned the pilot screw in completely and then loosened it by 3.5 turns. This time, no carbon on the plug but she was backfiring like crazy at high rpms. Guessing that she was running lean, I loosened the pilot screw another turn - same problem, I kept repeating this test and am now at 6.5 turns but she keeps backfiring. Am I doing the correct adjustment here? Am I turning the pilot screw the right way? Is there something else I should be looking at? The airfilter is cleanish, she has compression and there are no visible leaks from the exhaust I also checked the float height by eye and it looks ok.

Any advice I can get here would be really appreciated - I can't explain any of this to a local mechanic here. I've taken the carb out of the bike so many times that I'm going crazy.