ST1100 - SOLVE THE MYSTERY

Coming across the New York Thruway (I90) Friday, Frost started to act like the carbs were icing (RPMS drop, seems to be running out of gas). I dropped into a lower gear, eased off on the side and kept rolling along with a wide open throttle - figured I'd get as close to an off ramp as I could before she died. We went this way about 4-5 miles then all of a sudden she was back to her normal, happily running self. Noted conditions -

1. Temps were at least in the 70Fs and humidity was very low.
2. About 1/3 a tank of gas on the gauge.
3. Running characteristics were similiar to what happens when the carbs ice.
4. There is no vacuum fuel shutoff involved.
5. After the problem, the bike ran fine except the next day it did not want to idle at low speeds (acted like it was running out of gas). However, this morning it idles fine.

Thanks.

Failing fuel pump? Sometimes they are intermittent and tend to act up more with a partial tank of gas than when the tank is full. The theory being that when only partially submerged the pump tends to run hotter.

I like both of those answers....:bow1:

Crappy gas does not seem to fit. Fuel filter clogged should not "go away".

Any 'letric issues?

Hey Phil !

Nice having supper with you Thursday night !

Your bike prolly just got sad it was leaving New England :

If your bike returns to normal after a couple of tanks of gas, I'd probably write it off to bad gas. Have pulled the plugs to look at them ?

KAREN - I never completely close the fuel cap (poor grip after dual STT resections) but I will check it.

JEFF - The fuel pump is high on my list of usual suspects. Somewhere in the back of my mind I thought there was a relay also involved with the fuel pump.

PAT - Didn't seem to be electrical. It acted just like you were running out of gas (like when the carbs ice up). I kept the throttle wide open and it would still run along with greatly reduced power. Normally electrical seems to be off/on and this was sort of like it finally caught it's breath.

CHRIS - You're probably right. Could have been some of that chocolate cake got stuck in the fuel line ;-) ... The bad gas thing kind of crossed my mind also. Glad you and Dan could come up, my friend! BTW, I took 118 down and then 25C (instead of 25A) - both really great roads if they hadn't paved them with frost cobblestones!

I'm going to add one more possible suspect: Plugged fuel filter. I think mine was fuel breather plugged, but I changed the fuel filter at the same time...Once Once it was definitely the plugged line...

I'd like to explore the chocolate cake theory a little further before I discard it

RICK - Yes, please let me know what you come up with. If it would just fail solid, it'd be a little easier to fix it (I think). I've ridden a 1,000 miles since the incident without a hint of a problem.

TOM - It was killer chocolate cake at the Common Man in Lincoln, NH. If it wouldn't clog up the fuel lines, it would definitely clog up the waist lines ... ;-)

Fuel pump, it's fixable, too, if yur not afraid of disassembling a "no servicable parts" component.

Wish I would'a been less timid when my 88 Wing gave up on the way to Anna Marie Island a few years ago. (Same pump, known concern on the 1500s.)

But George, you can fix anything - including good grub! ;-)

"Microwave" noodles and Asiago Cheese with a can of tuna added, on the penny stove last night, Red Rock Canyon S.P. Oklahoma.

GEORGE - Sounds pretty good to me! Like I said ... ;-)

When my old Kawasaki got wet it would short out (or otherwise kill) the spark to 2 of the cylinders - a 4 cylinder bike suddenly goes down to 2 cylinders - kinda like when you are running out of gas (Some carbs still have gas in the bowls and 1 or more are empty).

I'd check the plug wires and ignition coils - not because they are wet - but if shorting out or not working properly that could cause the problem

My tardy $.02 worth - vapor lock.

Another possibility.... Could also be water in the gas, which could be intermittent. Never fill up at a station when the tanker is parked there (stirs up the stuff on the bottom of the tanks). But a wee bit of methyl hydrate (gas line antifreeze) will fix a water issue. I'm kinda leaning towards a dirty fuel filter too, but that probably wouldn't clear itself for long.

Well, I just solved (?) my similar problem. Turned out to be the fuel filter. I didn?t look at it sooner because it wasn?t that old and my problem was so intermittent. I cut the filter open and could not find any debris at all. The filter paper was discolored, maybe some kind of varnish or ?? I had 1psi of ?back-pressure? just trying to move fuel through the filter with the output hose hanging loose. The new filter shows no back-pressure now. Since the fuel pressure is so low on the 1100s it looks like a very small amount of restriction in the filter can be a problem.
On the bright side, I?ve learned a lot about the fuel delivery system and interlocks.

Rick

RICK - Hmm, the filter was causing your intermittent problem then?

Uncle Phil said:

RICK - Hmm, the filter was causing your intermittent problem then?

Click to expand...

Yep, I went 1000 miles between the first stall and the next one. Lately it got to be every few days.
Tried hard to duplicate with several passes from 0 to 100+ shifting at redline and several passes 0-100 mph with short-shifts to hold the throttle wide open as long as I could. Could not duplicate until I rode on the freeway for 20 + miles at a fairly high speed. I wired up a voltmeter and fuel pressure gauge to watch while the problem occurred. Gauges stayed normal this last weekend while it stalled twice. That?s when I checked the filter.

Rick

Good to know Rick.

Congrats on finding it and I think I might just change my fuel filter soon... 76k on my '01 now.

Thanks!
Mark