Symptoms: When moving at speed (happened anywhere between 15-50 mph), sudden (VERY) loss of power, with no response to throttle. Bike slows, of course, but engine somewhat curiously appears to remain "on." No odd behavior of dash lights. After a few seconds, power and throttle response return. Occurred about 6-7 times in ~60 miles of riding, but "clumped" into three instances, where it happened once or twice a few seconds apart. (27-mile each way commute, with a little midday driving in between.)
My first guesses were: Fuel delivery problem. Suddenness of onset and resumption of normal response suggests electrical cause. Or maybe water in gas? That pernicious fuel-pump connector under the tank? Of course also suspect fuel filter/hoses/pump. Absence of funkiness with dash lights (and a much less catastrophic-feeling failure) suggests it's not a recurrence of my previously jiggly kill switch.
Testing today found a faulty throttle position switch, but not in a way that could obviously cause the observed behavior. The switch tests in the "open" condition. That is, on a normal switch (or so says the one on my parts bike), the outboard pin and the center pin should be closed when the throttle is closed, and open when the throttle is open. (The center and inboard connector should be closed at WOT.) The presumed-faulty switch tests open regardless of throttle position.
So, this shouldn't cause what I'm seeing ... or could it? We know some people remove this switch, which would leave the bike in the position I found in testing: circuit permanently open. If, however, the switch's internals are loose, such that the contacting bits could jiggle into a closed position, it seems to me it could cause what I experienced. Can anyone confirm an occurrence of this? Is anyone familiar with the internals of this switch? I'll pull it apart tomorrow; just ran out of daylight today.
Today's diagnostics also included:
- Check battery terminal connections: fine
- Check ground to frame: fine
- Check spark plug & fuel injector connections: snug
- Computer connector: snug, contacts clean
- Pull & inspect spark plugs: fine
- FPR vacuum hose: lookin crusty, replace next week
- Crankcase vent hose: also crusty; order & replace
- Check & reseat tank connector: Looks fine
- Check for spark: Fine on all three zylinders
- Check fuel pressure: 36-37psi (stationary, of course)
- Drain tank; no evidence of water or crud in gas (vibration damper newish; < 10k miles)
In progress, to be finished on return of daylight:
- Replace fuel filter
- Replace in-tank fuel hoses with appropriate new OEM hoses
- Replace fuel supply hose (tank to fuel rail)
- Check that tank vent pipe is clear
On receipt of parts order:
- Replace crankcase vent hose
- Replace FPR vacuum hose
- Replace fuel return hoses
(Edited to add other diagnostics performed.)
My first guesses were: Fuel delivery problem. Suddenness of onset and resumption of normal response suggests electrical cause. Or maybe water in gas? That pernicious fuel-pump connector under the tank? Of course also suspect fuel filter/hoses/pump. Absence of funkiness with dash lights (and a much less catastrophic-feeling failure) suggests it's not a recurrence of my previously jiggly kill switch.
Testing today found a faulty throttle position switch, but not in a way that could obviously cause the observed behavior. The switch tests in the "open" condition. That is, on a normal switch (or so says the one on my parts bike), the outboard pin and the center pin should be closed when the throttle is closed, and open when the throttle is open. (The center and inboard connector should be closed at WOT.) The presumed-faulty switch tests open regardless of throttle position.
So, this shouldn't cause what I'm seeing ... or could it? We know some people remove this switch, which would leave the bike in the position I found in testing: circuit permanently open. If, however, the switch's internals are loose, such that the contacting bits could jiggle into a closed position, it seems to me it could cause what I experienced. Can anyone confirm an occurrence of this? Is anyone familiar with the internals of this switch? I'll pull it apart tomorrow; just ran out of daylight today.
Today's diagnostics also included:
- Check battery terminal connections: fine
- Check ground to frame: fine
- Check spark plug & fuel injector connections: snug
- Computer connector: snug, contacts clean
- Pull & inspect spark plugs: fine
- FPR vacuum hose: lookin crusty, replace next week
- Crankcase vent hose: also crusty; order & replace
- Check & reseat tank connector: Looks fine
- Check for spark: Fine on all three zylinders
- Check fuel pressure: 36-37psi (stationary, of course)
- Drain tank; no evidence of water or crud in gas (vibration damper newish; < 10k miles)
In progress, to be finished on return of daylight:
- Replace fuel filter
- Replace in-tank fuel hoses with appropriate new OEM hoses
- Replace fuel supply hose (tank to fuel rail)
- Check that tank vent pipe is clear
On receipt of parts order:
- Replace crankcase vent hose
- Replace FPR vacuum hose
- Replace fuel return hoses
(Edited to add other diagnostics performed.)