Originally Posted by Frost99999

I live in central FL, one of the most humid places on the planet :\

Originally Posted by griz11

Its the timing that is thrown off by going to a higher nitro %. A lot of people try to compensate by using the carb needles but that only goes so far. Head shims, Nitro % and plug heat range determine the timing. Change one and you have to change the others as well to keep the motor happy. The reason a motor will get hot with more nitro % leaving everything else alone is that more nitro advances the timing. Turning the needles to richen it up just puts more oil into the motor and cools if off a bit. The reason for this is that the nitro and the platinum in the glow plug wire cause a chemical reaction when put together under compression. Using the same plug the actual point of ignition will advance because you have more nitro to make the chemical reaction go. Get yourself a good loupe and learn to read the plug. That is the best way to make sure you aren't going to detonate a motor. A couple of things to look for in particular is if the coil is offset to one side after the plug has been run and the general condition of the wire. If the coil is offset you have too much compression, too low a deck height or its right on the verge of detonating. If the wire looks severely pitted then you are closer to detonating one than you want to be. The pits come from the platinum wire getting blown off by the higher than normal pressures developed in the cylinder. A couple of rules of thumb are

1. more shim retards the timing with the same plug and nitro%
2. less shim advances the timing with the same plug and nitro%
3. More nitro% advances the timing if the shims and plug stay the same
4. Less nitro% retards the timing if the shims and plug stay the same
5. Hotter plug advances the timing if the other two variables stay the same
6. Colder plug retards the timing if the other two variables stay the same

Start working with the plug shims and nitro% and you won't be messing with those needles near as much. A deck height gauge is a handy tool to have but you can measure the deck height with a piece of solder and a caliper as well. A motor will overheat if its too advanced or too retarded in timing. When its timed properly the exhaust will have a sharp cracking sound instead of a dull thud when it fires. And if you get out to the track one day and its super humid drop that nitro % and your motor will run better.

Griz