New here and have read a lot of the posts. I have a grubee 66cc Skyhawk just on the verge of being broke in. Today I decided to hammer a bit on it and it did really well for awhile. Then I noticed it loosing rpm so I backed off and let it go to half throttle. Ran great. I hit it again and no go. I pulled over to check it out. Looked at the plug all fine nice colour. Piston was good no scaring on the walls. What happened? Upon investigating I found the problem. The rear motor mount sheared off the bolts and was letting the motor tip enough so that the drive chain would rub on the housing. the more throttle the harder it would rub. I guess when I read on a post to replace all those china bolts I should have taken the advise. Oh well off to the auto supply tomorrow.