What I'm planning to lynz with is sections of coarse "barsteward"* round file, chucked into a drill. You might also be able to use a tap turning in a drill, one of the larger sizes (smaller than your port) with 5 or 6 slots down it would probably work better than one of the smaller ones with 4, since the edges won't catch so much when it's spinning. I'm going to be using the file though to try to get the antireversion |\|\|\ profile to them.

(*Thought the right word would trip the filter)

I have gotten as low as 40 mpg, depending on driving conditions. the weather has been cool, and this last tank was a combination of several short trips around town, and several 20 mile trips in the mountains. I am also running a couple of degrees retarded on timing due to a pinging problem I have had for some time. I am running ngk plugs with a hole drilled for better spark and am wondering if the sharp edges on the plug could be causing the problem. as far as the lynz mod,the bike seems to have good power, even with retarded timing, so I would say at the very least, they didn't hurt anything, and I would recommend giving them a try

in an aluminum head, it was pretty easy to tap them by hand. even if they are not perfectly round, a tap might still work. I would hesitate to use a drill, things could get out of hand if not careful

The plug mod might also be lighting the mixture off sooner, if it's throwing spark right out into the chamber instead of setting off a fizzle. Timing should be set for peak cylinder pressure at the right point, if that means retarding it, do it, it doesn't mean losing power.

I'm meaning a tap smaller than the port used like a burr.

I understand the advantage of getting the spark closer to tdc, and agree that pinging costs power and mileage. most people equate advancing the spark for more power and mileage, but retarding the spark can help you get over the wall, rather than running you into the wall. I never considered the plugs firing the mixture sooner, but that makes sense. I had to modify the trigger wheel to retard the timing since they only make wheels with more advance. thanks again for the info

IF it's got plenty of advance to play with, you could try lifting the dizzy, slipping it back by a tooth, and "advancing" to where you need to be. Stock from the factory, most vehicles are set up with conservative advance, so it won't ping on crappy gas. Hence peak cylinder pressure is some time after TDC and hence the "more advance = more power" thinking. With any vaporisation, ignition and mixture improvements, we might expect earlier peak pressure.

no dizzy, this is a 6 cyl. motorcycle with 6 coils, makes timing changes a little more time consuming, but not impossible, just modify the trigger wheel