My '81 van has sat since 2003,I did try to start it a few times every couple of months,but there were years it didn't get done,a few times it went about 16 months before I threw a battery in it and ran it off a gas can,but it always started up,though the carb did show signs of deterioration as far as the accelerator pump...
I was lucky it didn't seize,seeing we have damp foggy weather here often,and condensation can build up in cylinders quickly...being in a van probably sheltered the engine better than most other vehicles..
My diesel Suburban has sat since 2004 pretty much,and it had nearly a full tank of a mix of kerosene,diesel,and lord knows what other stuff the former owner used for fuel in it...I try to start that every 4 months at least,but didn't get too for longer periods during last winter when it was completely buried under a drift...over 8 feet !..
I was not up to shoveling it out and putting a battery in it,knowing dam well its chances of starting were practically nil in sub zero temps...it started up fine come spring though...
You should put a little oil like Marvel Mystery Oil in the cylinders if possible,if there is any surface rust on them and you just toss in a battery & gas it up and try whipping it over,could do some harm--a valve might have decided to stick shut after sitting,and it could bend a push rod ,the pistons could scuff up the cylinders if the have rust and are "dry"...I took the chance neither of my engines were in that condition,but I could have lost that gamble too..
Dont fill the cylinders up too much or you'll risk hydrolocking it..a teaspoon per cylinder is plenty..
I think the 307 in my van being rather tired and the valve stem seals allowed enough oil to build up in the cylinders each time I ran it to keep it "free"...diesels are usually more forgiving than gas engines when it comes to seizing up from sitting idle too,the fuel is a light oil,not a solvent,so the cylinders stay oily longer...
I like to ensure the engine is free by turning it over with a socket on the balancer bolt,and if no unusual resistance is noted it is OK to crank it over...I leave the coil wire off and crank it until there is oil pressure showing too (on a gauge or the light goes off)...this wont hurt anything and prevents dry starts..
If your lucky the fuel system will have survived--but if any gas was left in it longer than a few months,I'd not be surprised if you have problems ,like the fuel pump crapping out or not wanting to come on,leaky or collapsed rubber hoses,etc..good luck there..
