1990 Evinrude 9.9hp - Won't rev up

I'm looking at buying a 1990 Evinrude 9.9hp engine. The guy who is selling it says it won't rev up. It will start just fine and idle fine, but when you try and throttle up it just kinda sits there and bogs down. He says it needs a new throttle cam. He isn't willing to fix it because he doesn't have the tools to remove the flywheel or the time to do it. He's selling it for $400. This model has an electric starter on it.

Does this sound like a throttle cam issue? How hard is that to replace? I'm pretty mechanical and I've built automobile engines before, but I've never tinkered with an outboard boat engine.

Should I stay away from this thing or risk $400 for a motor that might only need a minor repair?

Thanks!

Carb may just need rebuilding. You should be able to manually throttle it and observe. Check the compression...if it's over 100 PSI it may be worth the money.

What exactly does the throttle cam do?

Throttle cam opens the throttle when cable is engaged.