If the engine will run nicely once it's started, then the problem with starting usually isn't due to an internal problem, though it may be a bit low on compression that gets better once the engine's had a chance to warm up.

To properly-set the carburetor...any carburetor, we start with a too-rich idle mixture, richen the high-speed needle, and start the engine at part throttle. We then get the full-throttle mixture properly-set. Only then do we retard the throttle and work on the idle mixture.

What fuel are you using? If the engine's starting to wear out, going to a higher-oil content fuel may help.

As far as parts are concerned, we'd not know where you might be able to locate any. The engine's been out of production since 1998, and parts for it are generally not available. You may be able to locate parts through an internet RC swap-shop site, or auction site. Perhaps checking the model magazines for ads from hobby retailers who collect parts for engine collectors may help.