Hi, I've had a few hyper 7s still got one in fact but none had the 21 engine. I had that problem with an onrd novarossi engine & had to heat the block with a heat gun, get a nitro heat sensor to check temp but you've gotta get it at running temp 220 F allso try loosing the glow plug a turn till it starts if that doesn't work. Check the high speed needle , it may be way too rich causing a hydro lock but that's only fixable by taking glow plug out & winding engine over to clear it out. It's possible that the needle settings are too rich , my manual settings wouldn't even start the engine. Pinch is a problem with all new engines but heating the block releases the tolerances so it'll wind over. Is the starter box full powered ?? A sluggish box will stop the flywheel as soon as it makes contact. BNEW batteries for starter box & when it does start try refilling engine while it's running for a few tanks, Don't forget to lean the high speed needle 10mins of a clock face, 5 or more usually does it, then fun of tuning low speed & adjusting idle. Too small an idle gap can make an engine too hard to start but you don't sound like that problem . Hope it helps. All hobby shops should have a nitro engine temp gun. Www.speedyrc.com has good deals unfortunately they're QLD but the spot to get your reading from is the glow plug or glow plug area. The old method was drop some spit on the head & if it sizzles off immediately it was too hot 5 seconds was a good heat to sizzle to.
Tony.