Ok guys this is my second conversion engine a 31cc ryobi to go into a 1/4 spacewalker any thoughts on this plane/combination? but the real question my motor seams to have a heck of a vibration near 3/4 throttle seemingly smooth on the bottom great idle and on top runs out strong. I have faced the flywheel aff and have balenced it in my prop balancer as well as the prop. I know that this is a hard thing to ask as I cant be specific about how much vibration but is this the nature of the beast at this throttle setting or should I keep looking for a cause thanks a bunch for any and all comments

looks like a case of plane structure resonance. (or maybe even rich burble)
Engine unbalance will work out over the whole rpm range. Hardly probable with a Ryobi.

Try the prop in different positions on engine. Have you also checked the prop tip to see if its running true. If you have a non-wood prop...try a wooden prop. also is the engine running rich at the worst viabration. All things to check. Good turn-out I hope. Capt,n

thanks for the help guys. I do have a master airscrew prop and do like the romance of wood so maby give that a go. But if it was an imbalance it would show through the entire rpm range and not just rear at the 3/4 throttle setting? Makes sense so could be a tuning issue? ok enough rambling to the shop thanks again guys any other ideas. Will this be a good motor on the spacewalker?

It should work out fine. Hope you can tame vibes down. Maybe on airplane...it will seem better???? Capt,n

thanks capn the wood prop seems to calm it down a bit and I belive that I may be causing a resonance though the radial moun that I made going to try to stiffen the mount up tomight and tey to get it mounted later or tomarrow again thanks for the help and encouragement

Just wanted to update you guys I have found that my radial mount that I had made was allowing a resonance (as was mentioned) made a new mount last night and ran two 16oz tanks out seems great. I am a bit worried that it will be heavy but just fly faster and smile right??

If the tail seems to viabrate....make sure to use some kind of braces like from near top of vertical stab to horizontal stab. Good Going Capt,n