[Zynice]

Can get feeler gauages from autozone or other similiar type stores for really cheap. Just make sure you get the correct size (0.005). Though its roughly the same size as a normal piece of paper. Wouldnt recommend a piece of paper for it but in a pinch can get give you a close guestimate. You mentioned it would idle but die off after a certain rpm. That sounds more like a fuel issue to me personally. Maybe a clogged injector or something with the fuel system. Can check to see if there is no kinks in any of the lines. But as you mentioned you took it to a mechanic and they said it would need a rebuild (assuming top end). Dont know many sources for dlx stock parts personally. If you want to go the big bore route could use MotoCult. Seen videos floating around online about them being used and people being happy about the results.