Is this "Herky Jerky" / TPS? - Suzuki GSX-R Motorcycle Forums Gixxer.com

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post #1 of 13 (permalink) Old 09-10-2018, 05:25 AM Thread Starter
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Is this "Herky Jerky" / TPS?

My 2006 GSXR 600 has approximately 24,000 KMs on the clock, and in the couple thousand KMs I've owned it so far, I've noticed what I think is the "herky jerky" throttle response.

If I am cruising along at say 50 km/h with the throttle at 0 and suddenly snap the throttle on to say 50%+, I notice a definite jerk/lunging motion as the bike begins accelerating. This occurs in any gear, although is more pronounced in the lower gears as they obviously have more "grunt".

The same things occurs the other way, if I am doing say 100 km/h at 6000 RPM with the throttle at anything over about 40%, and I quickly snap off the throttle, the bike again lunges/jerks, almost throwing me forward a little out of my seat.

It makes riding at a fast pace through corners difficult, as even with a gentle throttle roll on at high RPMs/speed, the jerk/lunging motion is uncomfortable at best, and upsets the handling/suspension at worst.

Never having owned a bike that has had this before, I'm not sure if this is the well documented "herky jerky"-ness that has been posted about.

Is what I have described the infamous "herky jerky" throttle? If so, I'll give adjusting the TPS a go and post back results.
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post #2 of 13 (permalink) Old 09-10-2018, 07:29 AM
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by endoftheline View Post
If I am cruising along at say 50 km/h with the throttle at 0 and suddenly snap the throttle on to say 50%+, I notice a definite jerk/lunging motion as the bike begins accelerating. This occurs in any gear, although is more pronounced in the lower gears as they obviously have more "grunt".

The same things occurs the other way, if I am doing say 100 km/h at 6000 RPM with the throttle at anything over about 40%, and I quickly snap off the throttle, the bike again lunges/jerks, almost throwing me forward a little out of my seat.
Quote:
Originally Posted by endoftheline View Post
It makes riding at a fast pace through corners difficult, as even with a gentle throttle roll on at high RPMs/speed, the jerk/lunging motion is uncomfortable at best, and upsets the handling/suspension at worst.
[...]
Is what I have described the infamous "herky jerky" throttle? If so, I'll give adjusting the TPS a go and post back results.
No. While this technically is herky-jerky throttle response, it is not caused by some fueling problem, or other problem with your bike, but by herky-jerky throttle input (by you). Let me elaborate: In first gear, a GSX-R 600 makes about 60Hp with wide-open throttle. Say it makes 40Hp at 50% open throttle. When the throttle is closed, engine and drivetrain losses cause you to decelerate, so in a way it makes negative horsepower, so when you "snap the throttle to 50%" you change the power output of the engine by more than 40Hp in an instant. This is going to cause a proportionate change in acceleration from braking to accelerating, upsetting the chassis as you note, and throwing your body backwards.

The situation is similar, only reverse in the case of suddenly snapping the throttle shut. The only remedy for this is not to do it. I don't know what other bikes you've owned, but the only way to get away with jerky throttle input on the scale you describe, is if the bike has a low power-to-weight ratio, computer-controlled throttle smoothing your inputs, or both. You also mention having problems when you smoothly roll the throttle open. This might be, in part at least, due to a "herky-jerky" throttle, but it may also be that your inputs are just not smooth enough. Finessing a throttle that changes power output by 80 or 100Hp from 0 to 90 can be hard, especially when that power is applied to a load of less than 300kg.

The "herky-jerky" is generally associated with the transition from that portion of throttle opening, where you're decelerating, to that portion where you're accelerating. Depending on gear and speed, the point on the throttle's travel where that happens changes, but your throttle input at that point is especially critical (for reasons that have been explained before and you can look up with a site search). It can also be related to the operation of the throttle when ever you open it from completely closed, or close it completely, in which case a properly set TPS is critical.

Finally and please don't take this as an attack on your riding skills, or personal insult, but your comments may be implying that your riding skill doesn't match the machine you're riding. If this is not the case then all is great, but if it is, it can be dangerous to you and those around you, so that you need to think about this as dispassionately as possible. Consider riding more conservatively until you gain some experience on your bike's behavior and response and on the potential dangers it may pose and accelerating your learning process by reading a couple of books on riding technique, attending a couple of riding school session, etc.
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post #3 of 13 (permalink) Old 09-10-2018, 05:09 PM Thread Starter
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by dpapavas View Post
No. While this technically is herky-jerky throttle response, it is not caused by some fueling problem, or other problem with your bike, but by herky-jerky throttle input (by you). Let me elaborate: In first gear, a GSX-R 600 makes about 60Hp with wide-open throttle. Say it makes 40Hp at 50% open throttle. When the throttle is closed, engine and drivetrain losses cause you to decelerate, so in a way it makes negative horsepower, so when you "snap the throttle to 50%" you change the power output of the engine by more than 40Hp in an instant. This is going to cause a proportionate change in acceleration from braking to accelerating, upsetting the chassis as you note, and throwing your body backwards.

The situation is similar, only reverse in the case of suddenly snapping the throttle shut. The only remedy for this is not to do it. I don't know what other bikes you've owned, but the only way to get away with jerky throttle input on the scale you describe, is if the bike has a low power-to-weight ratio, computer-controlled throttle smoothing your inputs, or both. You also mention having problems when you smoothly roll the throttle open. This might be, in part at least, due to a "herky-jerky" throttle, but it may also be that your inputs are just not smooth enough. Finessing a throttle that changes power output by 80 or 100Hp from 0 to 90 can be hard, especially when that power is applied to a load of less than 300kg.
The bike I had before this was a 1000cc V-Twin sport bike, so if I ever needed to know throttle finesse and control, it was with that bike!

I suppose re-reading what I posted earlier and your response to it, I might have exaggerated the extent to and aggressiveness of how I "snap" on the throttle, but did so to make it clear what caused the "jerky-ness". I don't experience it riding around town as I am not constantly on/off the throttle aggressively. I only really notice it when riding hard through the twisties or on the track.

Quote:
Originally Posted by dpapavas View Post
You also mention having problems when you smoothly roll the throttle open.
This is the part I find most annoying, as when riding hard, especially on the track where throttle control is crucial for cornering stability and correct apexes, even when being extremely smooth on the throttle, there is still definitely a "jerk" when it re-engages from decelerating. Although the smoother I am on the throttle roll on, the less jerky it is (but this is to be expected).

I may just give adjusting the TPS a go anyway to see if it has any effect - if not, I've only wasted my time!

Quote:
Originally Posted by dpapavas View Post
The "herky-jerky" is generally associated with the transition from that portion of throttle opening, where you're decelerating, to that portion where you're accelerating. Depending on gear and speed, the point on the throttle's travel where that happens changes, but your throttle input at that point is especially critical (for reasons that have been explained before and you can look up with a site search). It can also be related to the operation of the throttle when ever you open it from completely closed, or close it completely, in which case a properly set TPS is critical.


Quote:
Originally Posted by dpapavas View Post
Finally and please don't take this as an attack on your riding skills, or personal insult, but your comments may be implying that your riding skill doesn't match the machine you're riding. If this is not the case then all is great, but if it is, it can be dangerous to you and those around you, so that you need to think about this as dispassionately as possible. Consider riding more conservatively until you gain some experience on your bike's behavior and response and on the potential dangers it may pose and accelerating your learning process by reading a couple of books on riding technique, attending a couple of riding school session, etc.
I appreciate the concern but can confidently say it isn't related to my riding skill or ability. I've been riding for over 10 years and have attended a number of advanced rider courses, both on track and off, and regularly attend track days.
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post #4 of 13 (permalink) Old 09-11-2018, 04:46 AM
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by endoftheline View Post
This is the part I find most annoying, as when riding hard, especially on the track where throttle control is crucial for cornering stability and correct apexes, even when being extremely smooth on the throttle, there is still definitely a "jerk" when it re-engages from decelerating. Although the smoother I am on the throttle roll on, the less jerky it is (but this is to be expected).

I may just give adjusting the TPS a go anyway to see if it has any effect - if not, I've only wasted my time!
Ok, you seem to be an experienced rider, so let's assume the problem lies with the machine. There's been a lot of discussion on the herky-jerky, what causes it and how it can be fixed or at least reduced and you'd do well to research the matter, both here on the site and on the Net, before you start adjusting stuff. Besides the waste of time, there's always potential for deterioration.

I consider the problem open, in that I haven't found any conclusive, documented argument on what the case is, but my own theory is this: Besides the obvious causes, having to do with slack chains, work cush drives and other sources of added drivetrain slack, the problem can be caused by a maladjusted TPS, especially if it's set too low. In that case, the throttle passes through the correct setting, where the ECU perceives it as fully closed, before it has actually closed. If the ECU cuts off fuel at that point, it will cause a larger than normal deceleration, but the reverse case might be worse, as the ECU will turn on fuel with the throttle already slightly open.

It is also my theory that the problem has been so widespread mostly due to the fact that it's very easy to adjust the TPS too low due to the fast-idle mechanism. When the engine is not running and the ignition is on, a linkage between the secondary and primary throttle plates keep the latter a bit open, to aid in starting the engine and keep the idle speed high for a specified warmup period. This is essentially the same as if you've had kept the throttle open manually. If you adjust the TPS at that point, which is convenient and reasonable, it will be set too low (since it'll be at the proper setting with an open throttle). So my advice would be: adjust your idle speed as per manual, let the engine reach working temperature and check the TPS setting. If the dash is at the center, leave it be, otherwise research what it takes to adjust it (as it's easy to mess things up, by confusing the TPS with the STPS).
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post #5 of 13 (permalink) Old 09-11-2018, 08:59 PM Thread Starter
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by dpapavas View Post
Ok, you seem to be an experienced rider, so let's assume the problem lies with the machine. There's been a lot of discussion on the herky-jerky, what causes it and how it can be fixed or at least reduced and you'd do well to research the matter, both here on the site and on the Net, before you start adjusting stuff. Besides the waste of time, there's always potential for deterioration.

I consider the problem open, in that I haven't found any conclusive, documented argument on what the case is, but my own theory is this: Besides the obvious causes, having to do with slack chains, work cush drives and other sources of added drivetrain slack, the problem can be caused by a maladjusted TPS, especially if it's set too low. In that case, the throttle passes through the correct setting, where the ECU perceives it as fully closed, before it has actually closed. If the ECU cuts off fuel at that point, it will cause a larger than normal deceleration, but the reverse case might be worse, as the ECU will turn on fuel with the throttle already slightly open.

It is also my theory that the problem has been so widespread mostly due to the fact that it's very easy to adjust the TPS too low due to the fast-idle mechanism. When the engine is not running and the ignition is on, a linkage between the secondary and primary throttle plates keep the latter a bit open, to aid in starting the engine and keep the idle speed high for a specified warmup period. This is essentially the same as if you've had kept the throttle open manually. If you adjust the TPS at that point, which is convenient and reasonable, it will be set too low (since it'll be at the proper setting with an open throttle). So my advice would be: adjust your idle speed as per manual, let the engine reach working temperature and check the TPS setting. If the dash is at the center, leave it be, otherwise research what it takes to adjust it (as it's easy to mess things up, by confusing the TPS with the STPS).

Thanks, really appreciate your detailed and well written response.
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post #6 of 13 (permalink) Old 03-16-2019, 09:44 PM Thread Starter
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Re: Is this "Herky Jerky" / TPS?

A bit of an update on this thread - I finally got around to reading/adjusting the TPS as detailed in this fantastic guide: https://www.gixxer.com/forums/80-06-...ml#post2984331

My TPS line was initially right in the middle, and following the instructions in the above thread, I adjusted it so it was JUST on the high line mark.

A brief ride around town later and already I've noticed things are much, much smoother than they used to be.

Big thanks to @Duff8402 for their write up and instructions.

Hope this information helps someone else in the future!
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post #7 of 13 (permalink) Old 03-17-2019, 10:11 AM
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Re: Is this "Herky Jerky" / TPS?

I had this same problem on one of my bikes. With fuel low take a flash light look in the gas tank at the fuel pump and cycle the kill switch so the fuel pump comes on. While the fuel pump is priming your looking into the tank do you see any gas spraying around inside of the tank?
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post #8 of 13 (permalink) Old 03-19-2019, 05:43 AM
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by endoftheline View Post
My TPS line was initially right in the middle, and following the instructions in the above thread, I adjusted it so it was JUST on the high line mark.
So, it was in the middle with the engine running at proper idle speed and warmed up? And did you set it slightly high under the same conditions?
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post #9 of 13 (permalink) Old 03-19-2019, 01:13 PM
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Re: Is this "Herky Jerky" / TPS?

I think hes still having issues haha sounds like he used TPS to compensate for the issue instead of finding it.
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post #10 of 13 (permalink) Old 03-21-2019, 01:20 AM
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Re: Is this "Herky Jerky" / TPS?

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I think hes still having issues haha sounds like he used TPS to compensate for the issue instead of finding it.
No. Adjusting the TPS to slightly higher than middle may have solved the issue. It's true.
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post #11 of 13 (permalink) Old 03-21-2019, 05:38 AM
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Re: Is this "Herky Jerky" / TPS?

The thing is that, if you check and adjust the TPS with the engine stopped, or when it's not warmed up and in fast-idle mode, then the correct (i.e. OEM-specified) setting will read high and if you set it to the middle, it will actually be low. So one possible explanation for the whole problem, or at least for the cases that seem to get fixed by setting the TPS high, is that somehow the TPS has been set low, either because someone (say a mechanic[*] or a previous owner) has set it with the engine stopped (which is the natural thing to do and which the service manuals, at least the older ones, weren't very specific about), or perhaps because it drifted low. Then the current owner, in trying to fix the resulting fueling problems checks the TPS with the engine stopped again, finds it to be "good" but sets it "high", which is actually the correct setting and finds the problem fixed.

Whether that's actually how this "set it slightly high" rule came about, or whether the OEM setting is actually incorrect, I don't know, which is why I'm asking. It certainly was the case with my K4 though.
[*] I asked the mechanic at my dealership about how he sets it and the response was "with the engine stopped", so it certainly can happen.
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post #12 of 13 (permalink) Old 03-21-2019, 12:26 PM
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Re: Is this "Herky Jerky" / TPS?

Quote:
Originally Posted by endoftheline View Post
A bit of an update on this thread - I finally got around to reading/adjusting the TPS as detailed in this fantastic guide: https://www.gixxer.com/forums/80-06-...ml#post2984331

My TPS line was initially right in the middle, and following the instructions in the above thread, I adjusted it so it was JUST on the high line mark.

A brief ride around town later and already I've noticed things are much, much smoother than they used to be.

Big thanks to @Duff8402 for their write up and instructions.

Hope this information helps someone else in the future!
That's not fixing the issue. My bike runs spot on, and the minute I adjusted it to the high side like this bandaid "fix", it magically started riding like crap and having issues. Adjusting back to specs made the issue go away. Furthermore, if this was truly a fix that Suzuki just didn't know about, it would work for EVERY bike, which is does not.
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post #13 of 13 (permalink) Old 03-22-2019, 05:48 AM
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Re: Is this "Herky Jerky" / TPS?

Well one could argue that a "heky-jerky" type of problem, might result from many different root causes and if one of these is that the OEM couldn't get the TPS setting right, then fixing the setting yourself would cure the problem in those circumstances only. It seems a straightforward enough thing design-wise though, so I too find unlikely.

How exactly did it run "like crap and with issues" Just_Nick? I'm curious because, while I find it understandable how a small offset to lower-than-spec would cause a herky-jekry[*], I would expect a small shift to higher-than-spec, to not have much effect, apart from making the mixture slightly richer.
[*] Because the ECU would think that the throttle was entirely shut, when it wasn't so that it would cut off, or restart fueling when the throttle was part-open causing jerks both ways.
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