1/4 turn is a lot of fuel. The idle is a bit lean yet but more like only just the blade width of the screwdriver slot, or two. Making it more like 1/8 turn out from where it is now.
It may just be the accumulation of dirt and mineral restricting the space between the needle and the orafice. Sometimes turning it in until very lightly seated then backing it back out to the original position will crush and push the crud aside, restoring the space and fuel flow. If that doesn't cure it then a proper disassembly and cleaning is recommended.
Think about it. If the idle circuit is dirty wouldn't the main circuit also be dirty? Once the main circuit leans out a bit too much the lean mixture running wide open WILL melt the top of the pistons. And that costs far more than a carb kit and cleaning solvent. A slightly lean main jet won't give any warning, as it will be running far better than ever, until it melts down. Pay attention to your tach. If and when it ever runs so well that it RPMs a bit faster than normal, SHUT IT DOWN as it is soon about to melt. This is a critical warning sign, the power and RPM climb as the piston temp rises. Pay attention or pay the machine shop and partsman so your can rebuild your melted motor.
