Odd throttle response.

Hoping someone with a deeper knowledge on the tech involved in the throttle system can help figure this out.

I did a track conversion on my V4 last year, which involved taking most things apart, except I did not open the airbox/mess with the TPS or throttle bodies. I did change the throttle housing with the Ducabike race version, although I made sure to not pinch or damage any wiring.

Once everything was all bolted up and taken to the track, I noticed a problem that seemed to be a fueling issue. I have the T800 system, but the map I was using was used for 2+ years before the teardown without this problem. What was happening was the bike revving fine to 4-5 grand or so, then "hanging" for a few moments, surging hard afterward. The effect is very noticable when rolling on gradually, less noticeable with aggressive throttle.

I reflashed the T800 and the problem persisted. The next track day, before I could continue diagnosing it, my thermostat housing blew. While disassembling the airbox and whatnot to fix it, I checked the connections and the throttle system inside and found nothing out of the ordinary. Thinking perhaps the issue was related to the thermostat housing starting to give out, I fixed it, bolted everything back together, and gave it another go.

It's still there, and much more noticable testing it in neutral in my garage. If I start the bike and ever so gradually increase the throttle, RPM will increase and hold as it should smoothly until it gets around 4-5 grand and then it gets very erratic. I can hold the throttle at that specific point and the revs will bounce up and down without any kind of rhythm, like the fueling can't figure itself out. That entire "window" is erratic until the throttle has been rotated a few more degrees, then it surges to 7 grand or so and is stable again, responding as it should to throttle inputs.

I'm going to dummy check things like the air filter and throttle housing next opportunity I get, but figured it would be worth asking if anyone has experienced this issue before. If I can't find anything, I am considering taking it to the dealer for a full ECU reset to factory normals and see if that helps. Not entirely sure why the fuel mapping would suddenly go from fine for 2 years to not fine at all on the same map with nothing changed. That makes me think it isn't a T800 device issue, but it very well could be.

Edit:

I should probably clarify that my bike has the FM Project 3/4 system, sprint filter, and has no exhaust servo valve.

Check the clutch switch. Back in the day that was the first thing I looked at for an all of a sudden and spastic sporadic throttle. That’s assuming the V4 has one LOL

endodoc said:

Check the clutch switch. Back in the day that was the first thing I looked at for an all of a sudden and spastic sporadic throttle. That’s assuming the V4 has one LOL

Click to expand...

That's a good idea, will check that. It definitely has one since it has that cylinder deactivating feature at stops which instantly reactivates them the moment the clutch starts letting out.

Figured it out... kinda.

I was starting to think it was either TPS or MAP sensor problems, but right before ordering a MAP sensor to start troubleshooting that way, I decided to double back and test the T800 fueling aspect even though I hadn't changed anything with it for years.

Flashed the bike back to the original map and viola, despite a mountain of lambda sensor errors, throttle response was buttery smooth and linear. Flashed back to my T800 tune and it was back to being garbage.

Not sure what changed, maybe a firmware update ...... it all up or something. Contacted them to try and figure out if there's a solution, like giving me a different map to try or reverting to an older version.