Is the engine broken in? How many gallons through it? Here's the deal with most of these engines-we all,or most of us will run the lsn to lean opening the idle. In my experience it will seem like the engine is close in tune when in fact it is sucking fuel harder to keep the fat idle going. With that said on my 5 port I run byrons 30% with a os-p3 plug. The p3 plug is what you should be using right know with 20% The way things sit right now I would not remove a shim yet until you are sure the engine is broken in. Then I would put in a os-p3 plug,set the needles back to flush. Then turn the hsn in 1/2 turn-lsn 1 full turn and start from there. Also make sure your air filter is in top condition. and no air leaks. I went through all of this and more with my mg-66. With the help of some people on here I was able to tune it right and went from 7-9 minutes run time to over 12 min. Just remember to have engine up to temp before you try tuning,and make very small adjustments. And 99% of the adjustments will be to the lsn/idle. You will touch the hsn once? One last thing ,use temp gun only after engine is broke in and is running like a raped ape! Then that temp is only for reference. What I'm trying to explain here is that with the engine out of tune you will suck fuel like crazy. When I actually fattened up the lsn and reset idle,boom everything came together.