I have a coleman Generator 1850. It stalls when i

If the engine stumbles and falls with black exhaust smoke it is choked down and is incorrectly adjusted, do it without the air filter on.

goto COLEMAN POWERMATE 1850 SPEC/eHOW.COM

Try taking the carb off and clean using carb cleaner and blow thru all orfices with compressed air. I did this and now it runs like a charm!

your main jet is plugged shut off fuel, remove bowl from carb(bottom of bowl) clean out small holes on screw with stranded wire .2 holes on side on in middle. be sure to put fiber washer back between main jet and bowl and use fresh gas jor

When you drained the carb chamber by working with closed line, the floater in the carb chamber has fallen down. After two months later you let the fuel in again, the floater remain in down position and could not shut the input needle valve.

You may try to knock sharply (but not very hard) the carb cover when full, before opening carb cover in order to check the floater and valve. 

The lack of DC output COULD possibly prevent the stopping. There are likely fuse(s) between the low voltage winding and a rectifier to generate the DC. SOMETIMES these are even inside the generator cover.

Need more info,

Does it turn over??

Does it have spark??

Does it have fresh petrol??

is there an oilprotection on the gen. disconnect the cable and try again

Regular unleaded gas. 10W40 or mfg. suggested oil is fine.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/craig_3fa289bf857b1a3c

google it! use the specific search terms, Coleman power pulse 1850 - it worked for me!