stubborn screws.
Place whatever multitip bit that fits the screw head into the screw, with an extension if necessary. Then give a thwack to that bit/extension with something smaller than a hammer but bigger than a screwdriver handle. Sometimes I find the side of a 3/8 drive socket wrench or it's handle is good. The object is to send a jolt down into the screw head without deforming the screw head.
PS: If you have a partially stripped philips head screw then sometimes that 'thwack' on it's head can be delivered with a 3/8 extension. The blow will not only loosen the screws ninja grip but also deform the metal into the reamed out x ridges. Adding a little possible bite to your screwdriver.
Your results may vary.

I got them loose by vice grips after stripping the heads with the screwdriver ....a lil hard but they all came out. Still cannot believe the night and day difference in the bike after getting it to run right.

I used to curse at screw drivers and Japanese bikes. Then I discovered an impact driver with it's JIS(Japanese Industrial Standard) tips. Talk about a stress reliever in the tool box. Cheap and lasts forever.

You are so right.
Love the impact... LOVE IT! :)

And remember that the screws are pozidriv, not philips. That means that they are shorter holes, so if you only have philips drivers you may need to grind off the tip of the driver to get them to fit without damaging the screw head.

Yeah, I did that when you mentioned that a while back. No grinder but a small file worked with some muscle. That dang hardened tip was a real eye opener. Wrapped some tape on the shaft to identify the altered screw driver.