Here is an excerpt from an article I just read on timing. Interesting in regards to the low end loses if you advance too much. I would have assumed get a good timing and stick with it, not tune the timing to the track (assuming you travel to different tracks)
Probably the most commonly used ignition-tuning tool on the Briggs & Stratton 4stroke is the offset flywheel key. Every kart shop carries them and the savvy Briggs racer carries a selection to adjust the engine to the track. Basically, these little machined pieces replace the stock Briggs 1/8" X 1/8" flywheel key. Although they are sometimes marked in thousandths of an inch offset, more commonly they are identified by degrees of offset. In other words, how many degrees of crank rotation do they move the flywheel from the stock position. Most engine builders building methanol-burning Stock-class engines usually send their engines out the door with 5 degrees or so of offset. That amount of advance provides a reasonably safe performance increase without too many headaches for the less experienced or adventurous tuner. Part of that improved performance comes from starting the combustion process itself earlier and thus optimizing the point at which the combustion chamber pressure reaches its peak. Another part comes from the fact that the methanol/air mixture burns somewhat more slowly than a gasoline/air mixture for which the engine was designed. So you gas-classers out there take note; 2 or 3 degrees is a better place for you to start.
One thing to be careful of, silly as it seems, is that you offset the key the correct direction. You want the sparkplug to fire earlier in the crank rotation, when the piston is farther down in the cylinder on its way up. That means that, when viewed from the flywheel side, with the starter or starter nut removed, along with the washer, the keyway slot in the flywheel should be closer to top-dead-center than the keyway slot in the crankshaft, as the keyway rotates up toward the coil (Figure 4).
Ok out there, l see you rolling your eyes. But 1 have seen engines come in with the flywheels offset the wrong way. And believe me, retarding the spark 5 degrees or so won't do anything to help your performance.
Anyway, what happens when you move up or down from that 5 degree starting point? Offsetting the flywheel even more helps the engine achieve more complete combustion at higher RPMs. Starting the fire earlier, you know. But more combustion time in the cylinder means more heat absorbed in the block and head too. You'll gain top end but you'll probably need a bigger jet to keep the heat below the 380?390 degree upper limit. If you've blocked off part of the air intake on the fan shroud you may want to open that back up a bit. Most tuners aren't afraid to go up to 7 or 8 degrees, but few venture beyond there.
Unfortunately, that top-end increase comes at the expense of low end. And on track where getting off the slow corners is the difference between winning and losing, that's a poor trade. In cases like that, an experienced tuner reduce the flywheel offset to 4 or even 3 degrees to improve low RPM performance. Since the fuel/air mixture always burns, more or less, at the same speed, if you need the engine to be at its best at lower RPMs too much advance can move the peak combustion pressure back so early in the crank rotation that it actually resists the momentum of the crank and flywheel and hurts performance. Of course, to get the optimal fuel mixture at these lower RPMs, and to help get the heat up into the desired range, you may need a smaller jet if yon reduce the offset in the ignition. Closing off some of those air intakes in the shroud may help get the heat up too.