88 Honda Shadow VT600C long warmup time

I've got a 88 Honda shadow. Seems that the first run of the season it
always takes a real long time for the bike to warm up to the point
where I can crack the throttle.

I started it up yesteray for the first time this season and it had to
warm up for about 30 minutes before I could ride it. Before its warmed
up it will stall if you try to give it gas.

For as long as I have owned the bike the first warm up has always taken
a long time but seems to be getting worse as the years go by.

Any ideas what might be going on? I only ride the bike a few times a
year. Its only got about 4,000 miles on it.

Any hints of what to check are greatly appreciated.

The carburetors are gummed up. This happens with depressing regularity
to bikes that are left standing for a long period of time, especially
in warm weather, when all the fuel will evaporate from the carb bowls,
leaving behind a bunch of varnish.

Before you pull them off and disassemble the carbs for a proper cleaning,
try these possible fixes in this order:

1) Berryman's B12 in the tank.

2) Yamaha carb cleaner in the float bowls, use ONLY per the directions,
DO NOT PUT IT IN THE TANK!

I've had success with both methods, depending on how much crud there is.
You may also need to flush the tank or at least drain out the old
gasoline.