I've looked everywhere with varying results on how much to thin Nitrocellulose Lacquers for sraying.

I think I read somewhere that the sanding sealer coats should be 25% solids and 75% thinners and that colour and clear coats should be 50% of each.

Can anybody offer me advice on the subject from their own experience?

Thanks in advance, Phil

First post and i`m bringing a very old post back to life!
I find thinning to be down to preference. I`m doing sanding sealer roughly 90% sealer and 10% thinners, 3 or 4 good wet coats..and yes, i can get it fairly flat like this.
Top coats i use this little formula...Standard suction gun pot, 1 inch of paint, then add thinners to the 3 inch mark. For the final paint coat i thin further so i have a mostly thinners mix and stick it on....if done well you should get a nice smooth finish...or it can all go wrong and you get a finish full of runs!