Well, I'm definitely going to look into that. I'll get back with you on this post when I do.
I got this engine, NIB, at a swap meet for 200 bucks, and it came with a central hobbies pattern header. I use the header with no muffler, and it looks good and sounds even better on my seagull ultimate....
On the top end, it has lots of smoke. I can see the smoke from a long ways away. Mid throttle also has plenty of smoke, but the low end not so much, but it still idle's rough. Like you, I've chased the needle all over the place.
Well, instead of typing, I'm going to go get it out right now and look into it.
Thanks again...