Was reading somewhere that surge cause is unknown and the fix is installing iridium plug, which seems like an odd solution, so I decided to look in the carb for answers. Slide needle looks worn out, so I got new one and also emulsion tube, both are common wear items in some thumpers and twins, so it's worth a shot Parts came in a while ago and while I'm waiting for transmission washer I decided to go through the carb. I was unable to measure the emulsion tube ID but the needle has about .002in (.05mm) of wear comparing to new one. Doing some measurements of the taper it equals to about 4mm of up/down movement or in layman's terms raising the needle 5 clip positions, that would explain surging and large about of carbon build up n the combustion chamber after only 4,000 miles
