Bike won't idle when hot

I'm trying to get an '81 SR250 ("Exciter" model--don't laugh) running
again, after it sat in the garage for a few years. Now I remember why I
took it off the road--it dies when I come to a stop from running at
highway speed, especially in warmer weather. A bit of blipping the
throttle keeps it going, and it settles down after 20 seconds or so. The
carb's been cleaned, the air pilot screw and idle speed set for good
off-idle, and the bike runs fine otherwise (although starting takes a
few secs of cranking).

Anyone have an idea what I might check to pin this down? I'm trying to
get it running so my wife can get her m/c licence, and no way she's
going to put up with it dying at the stop lights.

 

Welcome to the wonderful world of the SR250!!
It can be a vacuum leak or one of the carb boots is leaking.
There is only one vacuum hose (to the petcock) so that's really easy to
check first.
Tighten the boots down on the carb. I like to run a THIN smear of silicone
on the mating surface of the boots so I get a good seal.
It can also be the flow of fuel.
Check the fuel filter (in the gas tank, attached to the petcock) is clean
and make sure the fuel line isn't kinked.
Then check the fuel level in the float bowl.
For all the SR250 answers you'll ever need, got to SR250.com
There is a set of "online" manuals there. (owners and maintenance)
D8
80 GS850G
8~ SR250s

 

Thanks for the link! I was wondering if it might be an air leak. The
rubber is pretty old and the hoses have hardened. I had a mechanic clean
the carb, but he couldn't find the problem.

I'm finding that some parts for the SR250 are unavailable, but the thing
is simple as a rock and I get a kick out of riding it, so I'm loathe to
part with it. However, I just picked up a new V-Star 1100 yesterday, and
it looks like the little thumper is gonna be neglected unless I can get
my wife to use it.

Coincidentally, I had a GS850G too. Great bike, but I only managed a
couple of good road trips over the years, so I foolishly sold it.

 

OK, so turn the idle RPM up far enough so the bike will idle while it's hot...[/QUOTE]

No, it idles OK, just sitting there--it's when I slow down from speed,
say taking an off-ramp and stopping at an intersection. Then it seems
like the idle circuit is totally closed, and only major blipping will
keep it going.

Hmmm...interesting idea. I'll check the clearances hot. They should be
close, but not touching I guess.

OK, good thought. I'm suspicious of the choke plunger assembly, since
the little boot looks rotten, and wiggling it sometimes affects the
idle.

It's the lampreys that really suck.