So I managed to get the 39 pwk installed last week and start tuning. It had the standard 172 main and 55 pilot jet from ATV Racing. After reading everything I could find about plug chopping/reading and carb adjusting I went out for some test runs. I too have run into the situation were you have to screw the slide stop screw all the way in to make it idle.....I didn't have to cut the spring though. After installing a fresh plug, I did my WFO runs to size the main jet.....the 172 seemed very close. That really surprised me, it seemed huge. The temp was about 55 degrees that day...so I may have to change that for winter.

Do you guys read your plugs down where the insulator meets the case? I always used to look at the ceramic in its entirety, but I guess that isn't accurate? Anyways, it had a nice mixture ring about 3 millimeters tall. I tried setting the air screw next.....with little success. Am I correct in assuming that the airscrew at the front of the carb will richen your mixture when turned IN? Less air means a richer mixture.......or am I backwards. My air screw seems to have very little affect on the overall performance.....even just affecting the idle speed. Is the pilot jet way too big?

Finally, I figured that I would try and set the needle. When running it wide open down the road, the motor (( Internal Combustion Engine ? )) would start to miss....."Blah, Blah" kind of sounds in the upper RPM band. I figured I was too rich so I moved the needle from the center clip to the 2nd one down....seemed to fix that until the temp went back down...now its doing the same thing again?

Hoser, I compared settings to yours and they seem alot different. Mine are all way fatter. I think I saw that you have a similar setup to mine so I thought that they might be alot closer.

This help with plug reading ? http://www.pilotodyssey.com/sparkplug.htm

If your air screw is not responding then you need to make a pilot jet adjustment, if you
turn it 2 turns out and it is still rich go smaller with the pilot jet, your adjusting when
the Engine is up to temp right? Adjusting it when the Engine is cold you probably will
not see much change.

Different Engine configurations requires different jetting, my whole setup is not one to
really compare to since my modifications are different than others, yours, my secret
squirrel stuff seems to have increased my carbs signal, made it strong, increased its
ability to pull fuel from the bowl easier requiring smaller jet sizes to slow the fuel
distribution down, it also mixes with the air better (more power) so is burned better.