tune up and dizzy springs

If the butterfly valve on the carb doesn't come all the way back to the idle position when you throttle back completely on the lever then you need to fix this first before you can expect your timing to return to it's base at idle. You might need a stronger return spring to pull back the throttle on the carb or your cable may need to be adjusted if it's not binding. So let's fix this first and I'll bet your timing issue will be fixed too. If not, we'll continue from there.

Any springs you buy from Summit are not going to be a direct replacement and you are going to spend lots of time trying to get your timing curve right if you go that route. Right now I don't know of a source to tell you to try for the springs. I bought a shaft for my distributor about 2 years ago and it came with springs and weights. So I have an extra set.

How are you checking your timing advance? Are you using a timing light? When you say "it doesn't come back to idle easily" are you refering to the timing advance or the engine speed? To check your distributor for advancing and retarding of the timing you need to use a timing light. The ones with the varible strobe delay (knob on the back) are best to use for this. If your carb doesn't return to idle easily you might need a new accelerator return spring. Are the springs you are looking at with Summit for a prestolite distributor? If not, don't waist your money, they won't be right. Marine distributors use heavier weights and springs than their automotive counterparts. How do your plugs look? If your don't know what they should look like get help here. If they are tan to light brown in color (the electrodes) and gap is good (.035") they are okay. If your engine isn't running good (poor performance, bad gas mileage,....) ignition is allways where to start. If you've tuned it all up and things still aren't right,..move on to the carb. The PCV valve dosen't need to be changed very often. If you shake it and it rattles, it's okay. Hope this helps! Write back if you have specific questions. I'll try to help.