ORIGINAL: 2walla
I would get the carb straightend out and make sure you have the timing correct before messing with the rings. I am pretty sure with a pro zinger and a can muffler that wasnt too restrictive that mine would turn 7100 with a zinger 18-10.. depending on now restrictive your muffler is you may not be that far off.. Are you sure some of the numbers guys are quoting are from running on glo?? They would turn 500-700RPM faster on glow than on gas.. Does your ignition advance the timing or is it fixed?
Your advise on getting the carb and timing straightened out before dismantling the engine is good solid advise. Start from the outside and work your way in.
There is a big difference between an 18x10 and a 19x7 which is my benchmark prop. 3" in pitch difference is a lot. 10" of pitch is pretty hefty. All of the specs I have quoted are for 92 octane gas and Stihl HP Ultra mixed at 40:1. Most guys tend to overprop but again...it depends on the application. Using an 18x8 would be comparable to the 19x7 since the 3W 19x7 is almost impossible to find in any make/brand now days. Always seems like that "magic prop" is unavailable. I will do a test run with an 18x8 and post my results but it may be a week till I can get to it.
I have two Walbro carbs that I use. The WT-540 and the WT-542.
HEY!!....I see ValleyView has XOAR 19x7's in stock. I think I'll by a couple or maybe three. :>)