ST1100 altitude problem?

Most of the time I ride my ST1100 close to sea level but this weekend I
crossed Stevens Pass (only 4100'). In both directions the bike sputtered and
lost power but it was worse on the return trip. In both cases the problem
immediately went away as soon as I crested the pass. 4100' doesn't seem like
all that much to affect the carbs so I'm guessing that maybe the added
incline disturbed the fuel flow enough to starve the carbs. Anybody familiar
with this problem and is there a fix? I'd hate to have it happen while
packing my wife with me.

JD

 

|| Jack Hunt <> posted in rec.motorcycles.tech:
||
||| On Tue, 07 Sep 2004 13:59:54 GMT, "JD" <>
||| wrote:
|||
|||| I'd hate to have it happen while packing my wife with me.
|||
||| Most people just let her ride on the back. What sort of luggage
||| are you packing her into? Will she fit in the side bag?
||
|| Considering that your wife probably *would* fit inside one of the big
|| Givi bags, I don't think you should talk, Jack.
||

Mine wouldn't fit. She's a 5'10" personification of Jessica Rabbit. I hope
to get her on her own bike someday or hope like hell she never gets a ride
on the back of an OldWing.

JD

 

Thanks, that makes a lot of sense,

JD

|| Sounds like you may be having trouble with the vacuum fuel valve, a
|| not entirely uncommon problem with the ST1100. It's located just
|| forward of the seat under the left side of the false fuel tank
|| cover. It's activated by a vacuum line to cylinder #3. When the
|| vacuum diaphragm starts getting flaky in these valves you start
|| loosing power whenever you apply full or almost full throttle. When
|| you go up in altitude you tend to use more throttle to make up for
|| the reduction in power. This in-turn reduces the intake vacuum and
|| if your vacuum petcock is getting marginal, it doesn't open fully.
|| As soon as you crest the hill and start down the other side, you
|| start using a lot less throttle, the intake vacuum comes back up and
|| your petcock opens more fully making the problem temporarily go
|| away.
||
|| You can test this by by-passing the valve (just study the plumbing a
|| little first) and test riding the bike. If this alleviates the
|| problem, it is indeed your vacuum petcock causing the trouble. K&L
|| makes a rebuild kit for this valve for about $20 and that fixed the
|| same problem on my ST1100. Don't forget to check the condition of
|| the vacuum line between the valve and the #3 intake tract too.
||
|| Good luck.
||
|| --
|| -WJB
||
||
|| ||| Most of the time I ride my ST1100 close to sea level but this
||| weekend I crossed Stevens Pass (only 4100'). In both directions the
||| bike sputtered and lost power but it was worse on the return trip.
||| In both cases the problem immediately went away as soon as I
||| crested the pass. 4100' doesn't seem like all that much to affect
||| the carbs so I'm guessing that maybe the added incline disturbed
||| the fuel flow enough to starve the carbs. Anybody familiar with
||| this problem and is there a fix? I'd hate to have it happen while
||| packing my wife with me.
|||
||| JD