I was working on the bike last night, tightening hose clips/filling coolant from when I cleaned up and replaced my thermostat a week or two ago. It was dark and most of my tools were at home and not at the lock up
Rode off to go to Tescopoly to clean me hands and buy a sneaky pork pie, 5 mile journey. Whilst creeping through town it became abhorrently clear to me that my idle speed was miles higher than it used to be. 1300rpm rather than 1050rpm. Also the bike had ditched its tendency to stall when launching (not a very scientific measurement/analysis) which it was awful for.
At Tesco's I went to tweak the idle speed screw and poked my head in for a peer to find it and spotted my mishtake. I'd forgotten to reconnect the crankcase breather back to the airbox.
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Now, plecebo added, because I now know something is different. The idle mixture now feels leaner - it hovers slightly dropping back to 1050rpm which I don't think it did before.
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At idle I would be surprised if the engine was pulling enough MAF to cause enough pressure drop in the airbox that an extra un-filtered opening would create extra airflow/less vac for the intake to breathe. Maybe I'm wrong, I could instrument it. But an airbox and filter setup designed to give enough airflow for WOT@peak power w/o much pressure drop should easily handle idle. -- 18month old K&N.
Maybe helmholtz? But at idle, they kinetic energy available is small.
Maybe the hose is creating a vac in the airbox from a depleted crankcase? Or a vac pulse at the wrong time, when the carb/cylinder is drawing? I placed a hand over the loose crankcase hose and there are very strong pulses but no net vac. It can lift and place back down my plastic id works security card from about 6mm gap.
Maybe oil sludge spewing in? Where the hose dangles is next to the casings. They look squeaky clean to me - although I've only done 20miles, and two WOT pulls. I've never found oil in the airbox.
Extra fuel molecules recycled back in adding to an already slightly rich mixture netting me an overall too rich mixture?
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Anyway, I'm not advocating it. I'm not about to continue to run with it all disconnected. I wish - ultimately to run a reed block and exhaust pulled vac - but that will happen the day I have nothing better to do. It was a simple accident and it's made my mind which should be worrying about a million far more important things in life wish to investigate this as a distraction to the aforementioned life.
Cheers,
Glen.