Hesitation on acceleration only after running for a while.

My '99 ST1100 starts promptly, comes off choke as usual, accelerates 90%
like new. But when riding at freeway speeds after an hour, I took off on a
back road. (time 4am, temp 40F, slight fog) As the road transitions from
turns to straights, and as I slow over blind hills so I don't strike deer, I
notice that the acceleration was terrible and there was hesitation, like
only three of the four cylinders were working. I was worried that the bike
would stall if I stopped it, but it never died. Once past the initial
hesitation, the bike would still leap up to the triple digits speeds without
missing or sputtering. When I returned to the city and was driving the
freeways , I noticed the acceleration problems and hesitation diminished
greatly.

At first I thought that the motorcycle swallowed too much water when I road
home in a driving rain catching all kinds of spray from the vehicles ahead
(temp < 45F). I change the airfilter, and ride around town with no
problems. So I think the bike is safe to ride this morning from Austin to
Dallas and this hesitation thing starts up just north of Waco and goes away
sometime while cruising down the HOV lane in south Dallas.

Is this temperature related? Or is this a result of really getting on the
throttle? For the first hour or so all was OK...

The temps should be in the 70s when I return home on the same path, so I can
check it then. Will turn 40,000 miles on same plugs. Have changed oil and
filters frequently using Amsoil products. Running fuel treatment now.

Carbs icing? Change plugs? Sync carbs? Ignore the problem?

-rh

 

Plugs look good. Did more research on web and the symptoms sound like carb
icing.

http://www3.telus.net/DonsMiniSite/MiniTek_CarbIcing.html

From the St1100.org website:
"Some early (pre 92 - L & M models) ST's suffered from carb icing. This
would typically occur after a period of constant high-ish speed running
(e.g. while cruising at 75 mph for an hour or so) in cold, high humidity
conditions. The symptoms varied from bike to bike, and not all were
affected, but one such manifestation was that the bike would lose power and
misfire.

The solution was to change the carb pistons, needles and needle holders
which, in Britain, Honda UK paid for. My 90 model (registered 91) was
modified about eight weeks after I bought it with 1600 miles on it nearly
four years ago and the cure is total."


The conditions were similar "...while cruising at 75 mph for an hour or so
in cold, high humidity conditions..."

Check on all of that. Only things is I have a '99 not a pre '92. Time to
talk to the dealer.