Jerking at low revs/speeds

[Fieldmouse]

Hello all,

I apologise upfront if I have missed any mention of this topic before, but I have scoured this forum and have not found an answer to my question.

Here goes.
My 14 is a 2007, standard, all except the clip on yoshi muffler which was on the bike when I purchased it.

Bike runs smooth as silk at idle, throttling on, throttling off etc. Problem is, it won't handle well coasting at low speeds, unless I really really really concentrate hard on holding throttle dead still! Making it a burden to ride.

So, fuel filter cleaned, new air filter, new spark plugs. Still the same. I've read up on TPS, throttle body balancing etc. Before I try all of this, I was wondering, does the ECU need to be remapped when a clip on muffler is fitted?

I've also noticed, bike will run fine at low speeds when it's cold, but not when hot. Could this be that when it gets to running temp, the fuel mixture leans out, and there's not enough back pressure due to different muffler.

I will re fit original muffler today and start from there. I know there's probably a multitude of answers to this, and again I apologise if I've missed a thread on this subject. Very frustrating, bike is absolutely beautiful to ride other than at low speed 🤷‍♂️

Thanks in advance everyone.

[KiwiCol]

Gidday Fieldmouse, welcome to the forum.  I see you've been a member for a while, but just not posted.

Now, this jerkiness at low speed & light throttle, chain tension comes to mind as does seized links. 
The ECU does not need a re-map for the Yoshi end can, so not much point in putting the bazooka back on.
Check the clutch switch isn't bridged & is working correctly, the ECU runs a different map at start up (richer) maybe yours is stuck on that 'start' map.

There's a wee 'trick' you can use & hear the maps being swapped.  Once warm, sit on it (at ldle) with clutch in and in gear, as if waiting to go from the lights, now just ever so slightly (before the clutch even takes up) let the clutch lever out n watch the rev counter, it should increase by a couple of hundred revs in anticipation of you taking off.  I believe that's the maps swapping in. Once you see it & hear it, it's quite obvious.

Try the things above, I picking chain myself.

[T 24]

Welcome Fieldmouse. How high or low is your idle speed when engine is hot / cold?

[Fieldmouse]

Hi KiwiCol,
Yep, been a quiet member for a while now, I try not to annoy anyone 😁. Mate, glad you don't reckon it's the exhaust, stuff me, the original is huge and heavy right! I've read how to check for bridged clutch, so I'll try that (how on earth does that affect the performance 😳). Anyway, chain is near new, and lubricated after every ride. Tension?, well I'm guessing too slack would create jerkiness? But cruises nicely in fifth and sixth gear without jerkiness. Do lower speeds create a more sensitive feedback through the chain than higher speeds??
On start up, revs shoot up to around 1800, but within ten seconds, it's settled at 1000rpm, where I've set it with idle screw.
I'll check map setting with clutch as you've stated what to do, and get back to you. Probably won't try that until Saturday. It's forty degrees outside at the moment, and fifty in the shed 🥵🥵🥵. Thanks KiwiCol, or in my best kiwi, Chur bro

[Fieldmouse]

@ Kotka, thank you for the welcome mate.
When engine is cold, it will roughly shoot up to 18-2000 rpm, but quickly settle down to 1000 rpm. When at running temperature, it's set to idle at 1000 rpm.

[Kiwifruit]

Check throttle cable adjustment, can make them jerky to ride slowly.

[BJ]

I have a 2006 (87000kms) which has the same symptoms at low revs. I have a Yoshi slip on. I have brand new chain and sprockets, brand new plugs, brand new genuine air filter, brand new new clutch switch and brand new new side stand switch. I've replaced the air tubes between throttle bodies, injectors cleaned and brand new Suzuki fuel pump and filter. Blanked off PAIRS. Shop set TPS and replaced some other ???sensor and it's running pretty good though a little rough on constant throttle around 3500. Not much else I can do. I think the biggest improver to date has been the new chain and sprockets.
I was reading about a guy who had the same symptoms and he wound his idle down to 800 and he said the jerkiness virtually disappeared. I have also wound my idle down to 800 and have to report that I got the same result. Much smoother below 2000. However I have taken the idle back up to 1000 and am suffering the jerkiness by hauling in the clutch at lower revs.
PLEASE let me know if you find a solution. Good Luck.

[KiwiCol]

Pretty sure the idle should be 1100.   Some knowledgeable chaps run theirs at 1200 - AlphaDave did.

[T 24]

When engine is cold, it will roughly shoot up to 18-2000 rpm, but quickly settle down to 1000 rpm. When at running temperature, it's set to idle at 1000 rpm.

Easy test.  Set your hot idle to 1100 to 1200 rpm. It may help.
I have to use 1300 to 1400 rpm idle speed, otherwise the turbo will stop totally on idle.
Only disadvantage is that sound when connecting first gear from neutral.

[Fieldmouse]

I have a 2006 (87000kms) which has the same symptoms at low revs. I have a Yoshi slip on. I have brand new chain and sprockets, brand new plugs, brand new genuine air filter, brand new new clutch switch and brand new new side stand switch. I've replaced the air tubes between throttle bodies, injectors cleaned and brand new Suzuki fuel pump and filter. Blanked off PAIRS. Shop set TPS and replaced some other ???sensor and it's running pretty good though a little rough on constant throttle around 3500. Not much else I can do. I think the biggest improver to date has been the new chain and sprockets.
I was reading about a guy who had the same symptoms and he wound his idle down to 800 and he said the jerkiness virtually disappeared. I have also wound my idle down to 800 and have to report that I got the same result. Much smoother below 2000. However I have taken the idle back up to 1000 and am suffering the jerkiness by hauling in the clutch at lower revs.
PLEASE let me know if you find a solution. Good Luck.

Wowsers BJ,
What haven't you replaced!!!😳
I don't like my chances now 😂. I certainly will let you know if I work it out. I don't like the idea of raising idle to 1200/1300 as mine clunks like hell when selecting 1st gear too. That's why I usually select 1st gear whilst rolling up to red lights to eliminate the load on the gearbox.

[Irish in Oz]

I think the biggest improver to date has been the new chain and sprockets.

Did you check the rubber cush drive behind the sprocket carrier.

[Eric GSX1400K3]

Replace the vacuum lines including the t piece connectors on all the throttle bodies,  plus remove and blank the pairs valves if that hasnt been done already.  Vacuum hose is really cheap off ebay, same with the connectors.

My K3 had exactly the same, i even replaced the clutch pack, front and rear discs, new tyres, engine oil, checked chain and sprockets, but nothing helped.

Changed  the vac lines  3 weeks ago and its a different bike....nice and smooth down low.

Oh, and the 1800rpm on startup then dropping down is the secondary throttle actuator working correctly, its designed for cold weather starts.  Idle needs to be 1100rpm, in my experience less than that and it increases the chance of stalling on 1st gear take off, too high and the shock load when selecting 1st can get a bit much

[Mick_J]

Had the same thing a couple of years ago and found the IAP or the AP (same unit) sensor was shagged.  These are the air pressure sensors in the vacuum lines Eric mentioned, I swapped them over and the symptoms changed so I replaced one with another I got from a forum member (don't know which was which  after several swaps) and the bike has been perfect since.  I also agree with Eric that tick over should be 1100 rpm for best results.

[DP1400]

I`ll go with Kiwifruit - check your throttle cable free play (and cable routing). If you don`t have the neccessary 2-4mm you`ll have a problem riding the bike smoothly on anything other than an opening throttle. OK, it doesn`t explain the cold/hot running scenario you`ve mentioned, but its always worth checking out the simple stuff before contemplating stripping the bike down.....

[Hooli]

I think this lot have already covered it, in my experience it's one of this & normally in this order -

too much slack in the throttle cables, I have mine as tight as I can without it revving as I turn the bars
chain slack
throttles out of balance
vac pipes from the throttle bodies perished

As to your question on how the clutch switch affects performance. When the clutch is in it switches to a 'starting map' which changes the fueling & ignition advance. If I run mine with the switch bridged it drinks fuel & backfires like a shotgun when I roll off.