I pulled the engine out of a Poulan 42 that run good and found the needles set to; High 1/2 turn and low 2 1/2 turns. I now have it in a plane and end up with about the same setting. But the high side doesn't seem to make much difference till it's screwed way out or almost all the way in. I have cleaned it and put in a new diaphram and pump kit. Checked and set outlet needle height. Also they are the same design. Not the usual long taper on the high side. Can I replace the high needle with something else and gain some adjustability? thanks

this is what happens when the low is set first if the high is not open far enough in the first place...The low needle is open too far...open both 2 turns, adjust the high first....The low will be open too far, lean it out until the transition is gone, then open a little at a time until the transition comes back....

I worked with it some more and kept coming up with the same thing. Also the midrange seemed to miss some. So I retarded the timing some and it still held the same top rpm. Also the carb needles now adjust a lot more like they should. The timing should have been about 28 to 30 unless I made a mistake. Retarded it at the field so I am guessing I took about 2 to 3 degrees out of it. Runs a lot better in the lower and mid rpm and seems to hold it's settings now. Also idles a lot better. Went from a 20x8 Zinger to a APC 20x10W and it runs smoother and lowered the idle by 300 rpm. Engine still needs some time on it though. But it looks promising now.

How do you change the timing, I assume you loosen the screws holding the coil and try to slide it, but there isn't much slop in the screws?

It's been converted to ignition.