OK, enough suffering, time for a trick or two. When to adjust valves: I open up the rocker cover maybe twice a year and use a feeler gage on my COLD engine and check the valve lash. If they are out of adjustment it's time to set them again. If your engine was running fine last week or last month but it sags now when you remove the ignitor it is usually telling you the glow plug is getting old. If it still does it with a new plug {not a used plug} then it is telling you the low end is a bit fat. Trick time!! With the new plug installed, engine running, remove the ignitor, if it sags then put the ignitor back on, lean the low end a LITTLE!! Remove the ignitor, if it still sags replace the ignitor and lean it a LITTLE more. Do this until it no longer sags. Now open up the low end just a LITTLE until you get a very slight drop in RPM. OK, low end is set. Now the high end will be a bit out of adjustment. SLOWLY bring it up to full throttle, twist the needle until you hit the max RPM then back off about 500 RPM, you should be good to go. Usually when your engine dies or sputters on take off it is telling you it is too lean on the high end. I found that dropping the engine that 500 RPM is about right for my four strokes. I used to try to get away with 300 but if the weather changed a bit I would have to twist my needle and I'm one of those guys that doesn't twist a needle for months on end. Nitro and a four stroke, nitro is not required but if you are going to use FAI fuel then you have to tune for it. Nitro makes getting one in tune a lot easier. I did a test one day on one of my YS 1.10s starting out with 30% nitro, I usually only run 15% with 18% blended oil. Not much difference with the 30%, a couple hundred more RPMs and a smoother idle. 15% was my normal so again, no big deal, 10% the low end was a bit rougher but it kept idling without any adjustments. 5% the idle was pretty bad and I didn't have the normal high end RPM, it was down a couple hundred. I could have tuned the low end for a smoother idle but I was just testing a bunch of fuel I was given. I ended up just mixing it together and using it up. No, you don't need nitro in a four stroke but you may loose the sweet spot on the low end and loose power. Nitro will give you a wider band to tune, make it easier and more reliable.