jonan,
You can soak them in anti-freeze in a crock pot to remove it. Take all the rubber and gaskets off of the engine, place it in a crock pot, cover it with anti-freeze (it must be the green kind and not the environmentally safe stuff), turn the crock pot on low (do not boil the anti-freeze) and let it soak. Check periodically to see if the crud is softening up. Once it starts to soften us an old toothbrush to brush it away.

There are a few warnings that go along with this. NEVER EVER use the crock pot to cook food again. It will be poisoned from the anti-freeze. Same thing with the toothbrush. Also, make sure you do this in an area with plenty of ventilation (not in the house) because the vapors are toxic.

Now with all of that said, why do you want to get the varnish off?? It doesn't hurt anything on the motor, and it's a lot of work to get it off. In fact, I would rather see a used motor with plenty of varnish on it. That way I know that it's been run nice and rich in it's life. A used motor that is all bright and shiny makes me think that it's been run lean and is probably ruin. At least that's they way I look at it. I've got more engines around here than I can shake a stick at and I don't bother to clean any of them. The run just as well dirty as they do clean!!!

Hope this helps

Ken