Jerky throttle in a low gear + hesitation + severe engine braking

[chopskey]

So this problem seems to randomly pop up and disappear, through the whole temperature range. I have no idea what it is. In a low gear, mainly 1st gear, the bike seems to be kind of sluggish until around 4k+ rpm at which points it starts to behave normally, but the second I close the throttle, it starts to engine brake EXTREMELY severely. Before it reaches the sweet spot though, the acceleration also seems to be sort-of hesitant. This is not the case when the bike is acting normally. I know the difference.

I know that the actual engine braking is already pretty high on the gixxers, but when this happens, the bike starts slowing down as if it's sluggish and like it's about to stall. If I apply throttle even slightly more than really eeeeeeaaasing onto it, the bike jerks forward. This happens even at a moderate speed of 25mph, so no, the clutch does not have to be pulled in. I know this is not normal because a few days ago, it wasn't doing this, and even today, it disappeared for a short ride and then later reappeared again.

Also, this problem does not occur in a higher gear. I think it's the worst in 1st and 2nd, but in 5th gear for instance, even at a speed of 40mph, when I let off the throttle, the engine braking is completely normal, the way it should be. Something is definitely off. What could this be? The TPS? SET valve? Too much oil? And why?

[Samantha750]

Try searching "herky jerky" and see if that is what you are experiencing. Sorta-kinda sounds like it but...
Could also put in dealer mode and see if the TPS needs adjusting. Too much oil should be easy enough for you to see if that's the case.

[chopskey]

Samschou, yeah I read that and it sounds a lot like it, but I didn't read that it was causing this extreme engine braking symptom as well. Maybe I missed that? Also, I did fill a tad too much oil, but the issue didn't appear after the oil & oil filter change. And, if oil were the issue, why would it happen in 1st gear but not 5th? I will try to do the TPS fix and report back, but could anyone explain exactly how this helps? And what the specific technical problem these symptoms are portraying is?

[Samantha750]

Well, TPS stands throttle position sensor. So basically it would give an inaccurate throttle position to the ecu which I'm guessing would result in inaccurate A/F ratios. I would think if you have 30% throttle but the TPS is reporting 8% and then suddenly it reads 30%, it would cause the herky jerky but honestly, this is just a guess on my part. Hopefully someone better schooled in this will come along and say I'm full of it and explain if I'm wrong.

[MacBayne]

you gotta give a little bit more info chopskey. mods to the bike? what does it idle at at rest? provided the thing isn't too much overfilled, oil won't do anything like the symptoms you describe. if it runs shitty below 4k, i instinctively go right to the battery. when the bike is off, test across the terminals and you should get over 13 volts. any lower, your battery is pooched. have you replaced the r/r? they are shitty on this generation. do the tps adjustment anyway, because it can be off on my bikes a couple of times a year.

[rv6john]

Do a search for kickstand/sidestand switch. I was going with you on the TPS but then you threw in the sporadic nature of the problem and that your description of the engine braking is almost like the bike is shutting off. Also, when the bike is not acting up, it runs well.

Lubricate the kickstand and make sure it is pushing the switch all the way. Otherwise you can bypass the switch temporarily (not a good idea to eliminate it) for testing. I think there is a thread on how to clean the switch, else replace it.

[chopskey]

MacBayne, no mods to the bike. The bike idles around 1200-1300rpm if I remember correctly. Recently changed the RR to an upgraded one. Battery is also new (about a month and a half old). I did have battery problems before, but never had issues like this. By battery problems, I mean the old battery would die after about a day. I think a defective RR had something to do with it too, but when the bike died and I measured the voltage on the battery, it would read like 9.7V (obviously the bike didn't start). My point is, even with the shitty old battery, where the bike would straight up die on me, the problems were not like this.

Regardless, I will check that too, but this leads me to suspect as Samschou has said that it's either the TPS, or as rv6john has said that it's the kickstand. Actually, now that that's mentioned, I did notice that the kickstand was acting a little funny, like I would have to use extra force to push it in, and it wasn't smooth, but very rough, just like it wasn't lubricated enough. But, does the kickstand switch have multiple stages of depression? I thought it was either activated or it wasn't. And if it wasn't, the bike would shut off if in gear. Anyone know?

[MacBayne]

do not rule out the battery until you check it with a multimeter, hell, you are putting it in dealer mode so the seat is off anyway. the sidestand switch is a good idea too. if either of those two things are not it (which tps probably isn't, but still worth a check) i would move on to the crank position sensor to see if it is plugged in.

[rv6john]

The kickstand switch is just a single throw, single pole momentary switch. It is normally open (not pressed) and closed when pressed by the kickstand being up. Otherwise the circuit must be closed (kickstand up)for the bike to start or run if the bike is in gear.

I think the problem is that the vibration of the bike, acceleration or deceleration or slight frame twisting(?) can cause the switch to open momentarily or vibrate open and closed. This would cause havoc as the ECU thinks you are putting kickstand up and down every fraction of a second. Same problem with a dirty or defective switch. Just not a good circuit.

Who knows if this is your problem. If you search, you will find a number of threads describing problems very similar to yours.

Good luck, and let us know what you find.

BTW. I don't think the bike will start or even run if the crankshaft sensor is unplugged. I have not read of any crankshaft position sensor failures anytime recently either, but didn't do a search.

[chopskey]

MacBayne, would the bike even start if the crank position sensor wasn't plugged in? Also, if it needed replacing, wouldn't I get a C12 error?

[chopskey]

Rv6john, I'm still not getting how the issue COMPLETELY disappears in 5th gear (I think it's also gone in 4th and 6th, and possible 3rd, but I don't recall exactly at the moment).

[MacBayne]

Originally Posted by chopskey

Rv6john, I'm still not getting how the issue COMPLETELY disappears in 5th gear (I think it's also gone in 4th and 6th, and possible 3rd, but I don't recall exactly at the moment).

if it disappears in 5th gear, i am going back to the CKP, and possibly the gear position sensor. they may not be unplugged, but it looks wonky. your bike has a different spark timing in 1-4, compared to 5-6, for emissions reasons. the thing is that a malfunctioning part of the electrical system will not necessarily throw codes. i went almost 2 years with a bad circuit for my secondary injectors/fuel pump and never got a single code. i thought it was the tps, because it was high in the revs. low revs problems are not normally caused by the tps.

[rv6john]

Originally Posted by chopskey

Rv6john, I'm still not getting how the issue COMPLETELY disappears in 5th gear (I think it's also gone in 4th and 6th, and possible 3rd, but I don't recall exactly at the moment).

I don't know. Different vibration levels? Sun spots? Again, I'm only relating what I've seen the last few years. And this is cheap and easy to check and correct. It could obviously be a lot of other things, but you have to start somewhere.

[chopskey]

MacBayne, I have heard the exact opposite, that the TPS fix addresses similar symptoms in low RPMs.

Regardless, I will start with the kickstand switch, TPS, and battery, and go from there. Also have heard of people resorting to a TRE to 'trick' the bike.

[chopskey]

UPDATE:

I lubed the kickstand, but this didn't solve the problem. Checked battery... normal. Adjusted the TPS... Boom, problem solved. Thanks guys.

[rv6john]

Good to hear you found the fix.

[ATXGixxer]

I'm looking to buy a 09 gsxr 750, guy is being deployed. It has been sitting for 6 months. When I ride the bike it hesitates around 2k rpm. The original 'herky jerky' thread happened near 4k rpm range..any help would be appreciated! Pretty decent asking price trying to see how easy it is to fix. I was thinking maybe some kind of tune up/spark plugs but don't know much mechanically about motorcycles

[MacBayne]

does it have aftermarket exhaust or filter?