2008 650S unwanted WOT

[NotInclined]

First time poster here, looking for the accumulated wisdom of the collective.

Here's my tale of woe. The "throttle" on my -08 SV650 stuck wide open towards the end of a straight at last weekend's event. This was during the first lap of the third session of the day. I managed to come to a somewhat controlled stop, and shut off the engine. The handle would open and snap shut just fine, so the throttle cables weren't stuck of impinged, yet the engine would howl and bounce off the rev limiter. I moved the bike to the paddock under its own power between sessions, afraid I was going to burn the clutch while doing it. After letting the bike cool a minute I tried re-starting the bike with the same results - WOT. I came back to the bike after another 15 min and - lo and behold - it ran just fine.

The bike doesn't have any gauges, that's how I bought it. The gauges were pretty crudely removed, leaving a tangle of wires under the tank. The only "work" done on the bike to track down issues was moving some of loose wires ending below the throttle body toward the back of the bike. Anyway, I decided to take my chances on a recurrence and ran the bike the rest of the day, four sessions, without incident.

A couple days later I had a chance to look under the airbox. I had mounted a new-to-me K&N air filter a few days before the track outing so that had recently been cleaned and free of debris. In and around the throttle body assembly, I found
- both cables from the throttle handle in good shape, very little slack
- nothing to obstruct the spring mechanism on the clutch side of the bike that is actuated by the cables from the throttle handle and which rotates the spindle that opens / closes the front throttle butterfly
- nothing to obstruct the movement of the rod situated on the opposite of the front cylinder throttle body which moves back and forth to open the rear cylinder butterfly in unison with the front one
- nothing to obstruct the rotation of the spring unit that rotates the spindle for the rear butterfly
- no signs of any debris inside the throttle bodies that could have caused them to stick wide open.

Having not found anything, I sprayed some MAF cleaner on all rotating parts, wiped off some dust on the outside of the throttle bodies, and buttoned up everything. While doing that, I made sure no wires or hoses could obstruct any moving part, and that the rubber boots around the throttle body openings are properly tightened.

Seeing that all parts are mechanically actuated and the cables, spring mechanism thingies and rods that move these parts are working as planned really didn't provide any answers. Thinking back, while the engine was screaming WFO, the throttle handle would still snap back just fine without any corresponding change in RPM. I tried opening the throttle and letting go of the handle while holding in place the rod that controls the movement of the rear butterfly. The handle would not snap back or move at all, i.e. if the rod or the spring mechanism movement were obstructed, the throttle handle wouldn't have snapped back freely.

Somehow the engine kept being fed gobs and air fuel, regardless of the position of the throttle handle that, I've now confirmed, appropriately controls the opening and closing of the butterflies. I just don't know how. I also checked the condition of the rubber boots and couldn't find any obvious drying or cracking.

I did find several threads on this forum re: TPS settings causing late opening of the butterflies. Would a loose TPS potentially cause an unplanned and uncontrolled (by the rider) opening of the butterflies? Which then would correct itself without any mechanic intervention? I haven't had a chance to specifically look at the TPS to determine whether the torx screw holding it in place is loose. Even if it were, would that cause the WOT condition? How would I fix it? As I mentioned earlier, the bike doesn't have a gauge cluster so I can't determine the current idle RPM setting from the dash.

I'd welcome any ideas, solutions, even wisecracks at this point.

[Seeker]

Could the butterflies be sticking when hot? If I recall, the ECU only controls the secondary butterflies which are the upper ones and that's only to stop the engine dying if blipped.

What happens if you unplug the TPS - I know you would normally get an FI warning light but I don't know if it will run without?

[NotInclined]

Originally Posted by Seeker

Could the butterflies be sticking when hot? If I recall, the ECU only controls the secondary butterflies which are the upper ones and that's only to stop the engine dying if blipped.

What happens if you unplug the TPS - I know you would normally get an FI warning light but I don't know if it will run without?

When this incident happened, I was on my first or second lap out so the engine wasn't that hot yet.

I have now verified that the TPS is securely attached, couldn't rotate it around the screw, and could only tighten the screw by about 1/16 of a turn. I didn't try unplugging it, though.