Re: need homemade brew for applying decals
Sounds like we may be talking about different things here. Are you applying waterslide decals, or vinyl stickers? I've used the recommended soap solution for "stickers" and had good luck, but I've never had soapy water work well with a true "decal".
If you are using the old fashioned OB motor lacquored water slide decals, then dishsoap is the least of your worries. There are only a few sources for these reproductions and some of them are very thin and tear easily. They don't lend themselves well to compound curves. Before you even start, coat them with a clear acrylic spray like Krylon. Then cut them out of the paper backing because the overspray on the paper will make a mess.
Use warm (not hot) water to soften the glue...I use about 90F water. I prewet the engine part with hot water first, then slide the decal off the paper onto it.
Let it airdry for 1 week minumum before topcoating. Use a clear enamel from a hobby shop and brush it on the decals, extending the coating to about 1/4" beyond the decal. This will best duplicate a factory job. If you chose to clearcoat the whole engine, be sure your topcoat is compatible with both the engine paint and the Krylon on the decals.
The larger the decal, the harder it is to apply. I have applied single decals to a single flat surface and not bothered to precoat the decal. The hardest ones are the old square tank outboards, where the decal wraps around 3 sides of the tank.
