I'm guessing the last guy who messed with the fuel mixture didn't realize that the WOT switch was busted (stuck always on). So he/she turned the K-jet fuel mixture WAY lean (counter-clockwise). It was so far down that it took basically one whole clockwise turn to get the duty cycle to show something besides 95%!
Anyway, yesterday I realized that I have an o-scope that I could use on this to REALLY see what's going on (DUH!). So I busted it out and made the measurements, it's cakewalk with this setup. Then I hooked both the cheapo dwell meter up and my o-scope and shot the video so you could see what I was seeing once I had it dialed in.
These are o-scope shots of the experiments from the manual:
So what WAS the problem getting the allen wrench into the mixture screw?
The problem was that I had a cheap set of allen wrenches. I was using a large set that I bought at harbor freight long ago, they are made of the black material. Trying to use the wrench in that screw top ended up rounding out the allen wrench. I went to a friend's house who had another 3mm allen, but it was black and had a ball end. I told him I was looking for a flat-ended one and he took it to his grinder and removed the ball. He let me borrow that one and it got rounded out too but I was able to enrich the mixture a little before it became unusable. I have a set of silver metal allen wrenches but they are on a ring and the long end is attached to the ring so I am unable to use those for this application but they seemed much higher quality and less likely to become rounded.
I was toying with the idea of using JB weld to shore up the insides of the screw top so that I could use the allen wrenches that I had, when I decided to purchase some good silver allen wrenches as a last-ditch effort. I looked around in town but nearly everything I found locally is made of the black material. Last week I ordered this set of silver metal Bondhus allen wrenches from amazon. They are MONEY and work very well for this application. No slipping, no rounding, no issues. Last night I tried it out and was able to turn the screw and dial in the mixture.
When you grind an allen wrench you destroy the hardening making the wrench much softer and easier to round off. Instead of a "set" all you needed was 1 tee handle 3 mm allen wrench. Glad to hear you got it sorted out. Make sure you use a good plug that won't come loose in the hole over the mixture screw.