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twist
06-22-2008, 05:56 PM
Is it me or is it the bike??

Here's the question: when cruising, usually in a lower gear (3rd , 4th), at around 4,000 RPMs - or higher (?) - any sudden movement that causes the throttle to close, even a little, really causes the bike to lurch (sudden deceleration), jerking me forward.

Small bumps in the road can make it happen easily too, sometimes causing me to bounce around trying to settle things down again. It's not extreme, like dangerous, but it is very noticeable (to me).

I was playing with this today trying to recreate the conditions and see if I can control it. It is SO sensitive it really makes me wonder if it's me or some kind of adjustment I need to make.

It doesn't always seem to do it either, maybe it's the temperature, maybe the RPMs, maybe gear selection - maybe it just me.... :giveup:

Anyone notice this? Is this just how modern bikes are - or should I get checked for Parkinsons?

Thanks :rider:

PhilS
06-22-2008, 07:06 PM
Is it me or is it the bike??

Here's the question: when cruising, usually in a lower gear (3rd , 4th), at around 4,000 RPMs - or higher (?) - any sudden movement that causes the throttle to close, even a little, really causes the bike to lurch (sudden deceleration), jerking me forward.

Small bumps in the road can make it happen easily too, sometimes causing me to bounce around trying to settle things down again. It's not extreme, like dangerous, but it is very noticeable (to me).

I was playing with this today trying to recreate the conditions and see if I can control it. It is SO sensitive it really makes me wonder if it's me or some kind of adjustment I need to make.

It doesn't always seem to do it either, maybe it's the temperature, maybe the RPMs, maybe gear selection - maybe it just me.... :giveup:

Anyone notice this? Is this just how modern bikes are - or should I get checked for Parkinsons?

Thanks :rider:

You know, I did not read too thoroughly through the other posts, but have you tried going into dealer mode and seeing if -COO or _COO show up on the odometer to see if the TPS is OK?

Trailduster
06-22-2008, 10:10 PM
Your not alone on this, I'll go up a gear, at 50 im in 6th cruising with one hand on the bar , The more you lug it a little the less you have of the quick throttle response, BUT if im approaching an intersection and or cross traffic, I drop a gear and put it in this mode where it will decelerate quick on letting off the throttle and put both hands on the bars.:sun:

suzukijo
06-22-2008, 10:17 PM
ok, i'll bite.
cruising, at 4k in third.
without going out and riding, i would think thats about 60mph.
i would be only doing that, if i wanted instant acceleration, and instantaneous response from the engine.

that is where you are at.
put it in high gear instead.
downshift if you need to romp.

one peculiar riding habit i have, (among others) is i slip the clutch.
i use the clutch, i find, on every upshift and every downshift, unless i'm trying to catch up, but i still use the clutch even so, no slipping.
i find myself in turns, pulling in the clutch to let the bike 'fall' into the beginning and slip it coming out making a smooth exit.

for me, its just me. its old dirt riding habits.

try this.
if the bike is too sensitive at that low gear, instead of chopping the throttle, pull the clutch in.
for me its a response, not a function.
i dont mean to do it, it simply happens.

my guess, is your putting the bike right at that rpm, that makes is responsive, and ready to go, like your ready to pass cars, or race your buddy, or about to wheelie. sort of like putting a nickel on a knife and saying its difficult to balance it when its on edge like that? laying the knife flat and the nickel flat, its easier to balance. shift to high.

off topic, i find myself shifting to neutral at speeds of 60-70 mph.
snick snick snick snick, its in neutral. that might work for you too? i dont know.

Trailduster
06-22-2008, 10:43 PM
It may be harmless to run down the gears to nuetral at 70 -60 mph, in all my years i've always waited to where im traveling at the speed i would be running in that gear before i click to it even though im on my way to nuetral ,on street bikes anyway, Dirt is a totally different story where you gear down to first on the fly while the rear end is bouncing all over the place, sling it around the tree and blow a roost in the guys face behind you.:lol2:

Brass
06-23-2008, 09:23 AM
Anyone notice this? Is this just how modern bikes are - or should I get checked for Parkinsons?

Thanks :rider:

Twist,

The technical term for what you're describing I believe is dynamic engine braking. It's more pronounced on large displacement bikes or v-twins.
When you close the throttle, the engine is demanding more air/fuel than youíre supplying. This causes the engine to want to slow down to the point where its rpm will match the supply of air and fuel being delivered. There are points in any engines rpm range where this is more pronounced. There is also a point in the rpm range were the rotating mass of engine overpowers the effect. In other words, when the engine is spinning so fast that its inertia lessens the effect. The same things are still happening you just donít notice it in such a pronounce way.

The basics of it are that every motor is affected by it. Bikes however deliver those effects directly to the rider. Some bikes more than others. A 400 lb 600cc bike with a 180lb rider wonít feel it as much because the total mass of the bike and rider easily overpower the effect. Increase the displacement to 1000cc or more and closing the throttle will have the back wheel skipping and chattering.

Slipper clutches were developed to counter the effect.




one peculiar riding habit i have, (among others) is i slip the clutch.
i use the clutch, i find, on every upshift and every downshift, unless i'm trying to catch up, but i still use the clutch even so, no slipping.
i find myself in turns, pulling in the clutch to let the bike 'fall' into the beginning and slip it coming out making a smooth exit.

for me, its just me. its old dirt riding habits.



Joe,

It sounds like you ride your bike like it's a 125 2 stroke. :rider: (oh how I miss the good ol'days)

Have you checked out your clutch and basket for wear? I'm wondering how it's holding up. Your riding style would accelerate wear and find any weakness in there. Not that I would expect any but we are talking about a "new" transmission in the Bandit.

A1A
06-23-2008, 11:46 AM
Thats the 79 Ft. Lbs. of torque at work for you.

achesley
06-24-2008, 08:46 PM
I ended up putting a throttlemieser on mine and find just a little drag help keep the throttle more steady and smoother. Just a little tighter lets you just rest your right hand totally. ;-)

Dink.1170
06-25-2008, 03:56 AM
My Bonnie must be very well setup, I have noticed none of the issues most are reporting. No surging; even with a Micron pipe fitted and no other changes, un-corked BTW, throttle sensitivity is not worse than CV carbs, idle is stable and smooth, the seat is a little hard; my milage is very low (3700kms) though,screen is fine; now that I have lowered the handlebars, the originals were too high and too wide.

Dink

hawk GT
06-25-2008, 04:35 AM
My Bonnie must be very well setup, I have noticed none of the issues most are reporting. No surging; even with a Micron pipe fitted and no other changes, un-corked BTW, throttle sensitivity is not worse than CV carbs, idle is stable and smooth, the seat is a little hard; my milage is very low (3700kms) though,screen is fine; now that I have lowered the handlebars, the originals were too high and too wide.

Dink

The Micron pipe increases flow from the stock pipe, thus decreasing backpressure and in turn decreasing the prominence of engine braking.

hawk GT
06-25-2008, 04:41 AM
Is it me or is it the bike??

Here's the question: when cruising, usually in a lower gear (3rd , 4th), at around 4,000 RPMs - or higher (?) - any sudden movement that causes the throttle to close, even a little, really causes the bike to lurch (sudden deceleration), jerking me forward.

Thanks :rider:

Which bike are we talkin' about? The Bandit or the Shadow? What is the set-up for the bike in question? What is redline for said bike? These question should be asked before an opinion should be given.:zen:

bones
06-25-2008, 08:59 AM
http://www.twtex.com/forums/showthread.php?t=29150

twist
06-25-2008, 09:52 AM
Bones, I've had the cutting out incident as well, (noted in the thread you started) my question about the throttle is different in nature - I have not had a repeat of the 'cutting out' problem since the one I reported (which felt a lot like running out of gas).

I think within all the great replies posted here is the answer to my question, the very high torque of the Bandit, combined with high RPMs (4,000 is high?? - "cruising" in traffic wanting a quick response available btw). And maybe something to lessen the sensitivity of the throttle in general (should every bump in the road be accompanied by a sudden throttle response, slowing or accelerating? I don't think so)

:rider:

vamacher
06-25-2008, 10:41 AM
I have noticed this too. Usually when I am in a lower gear coasting up to a light. If I bump the throttle accidently it will just about yank me off the bike. It reminds me to pay attention and hang on.:eek2:

achesley
06-25-2008, 11:56 AM
Triumph used to come with a little screw to dampen the throttle a bit way back in the 50's. Just for that reason, throttle control on the ruff roads we had then. Now, use a throttle lock for the same reason, Dampening.
Heck, the old Harley with the screw type throttles, it was where you left it. Had one that would vibrate towards open when taking your hand off the grip. Was kinda worn out.;-)
I took a Vista Cruz off my KLR for the reason of when bumping the thing accidently, the throttle would slam shut. Find the end bar friction devices to work better for throttle control.

Huladog
06-25-2008, 01:37 PM
Could be the fuel cut-off inherent in the FI systems, they literally cut all fuel off when you chop the throttle (emissions stuff). Yes, it does feel like your engine died and you've got max engine braking going on since it's like the engine isn't even idling.

I added the TFI from Holeshot and used Dale's secret settings, seems to help a lot but I can still encounter it in 6th running about 3,500 rpm. Below that, no problem. Above that, no problem. Not as drastic fuel cut-off but you can still feel it.

If I weren't so lazy I might tweak the TFI settings bit to get rid of it.

Aloha,
Huladog

sproggy
06-25-2008, 02:20 PM
The Micron pipe increases flow from the stock pipe, thus decreasing backpressure and in turn decreasing the prominence of engine braking.

No it doesn't - the exhaust has nothing to do with engine braking.

Dink.1170
06-25-2008, 03:22 PM
The Micron pipe increases flow from the stock pipe, thus decreasing backpressure and in turn decreasing the prominence of engine braking.

Btw having worked in motorcycle exhaust design and manufacture, I am well aware that a decrease in back pressure will increase the prominence of engine braking, the reduction in backpressure allows the engine to respond faster.

Dink

Jack Giesecke
06-25-2008, 03:33 PM
Twist,

The technical term for what you're describing I believe is dynamic engine braking. It's more pronounced on large displacement bikes or v-twins.


I've always called it "compression breaking" and it's why I don't like 4 stroke twins on the track. Heavy breaking on a big twin requires clutch control OR a slipper clutch to do the work for you. I am a 125 two stroke kinda guy, or 80 or 250. :mrgreen:

hawk GT
06-25-2008, 03:38 PM
No it doesn't - the exhaust has nothing to do with engine braking.

Wrong. Sorry to be so blunt but a blunt reply deserves bluntness in kind.

hawk GT
06-25-2008, 03:39 PM
...

hawk GT
06-25-2008, 03:43 PM
Btw having worked in motorcycle exhaust design and manufacture, I am well aware that a decrease in back pressure will increase the prominence of engine braking, the reduction in backpressure allows the engine to respond faster.

Dink
I only know what I've experienced ( on many bikes that have been turned from stock to pipe/jetkit/aircleaner mod ), so whatever you say chief. The bike slowed down ( engine braking ) slower ( with less torque ) after the mod. Think about it you are cutting the fuel and more air is flowing through the system than before ( less back pressure ), less torque, slower slow down. Good luck.......

suzukijo
06-25-2008, 06:42 PM
interesting topic about ex back pressure causing increased decel drag, or not.

since there seems to be a couple experts here, how bout a link to information if you dont have time to explain it, i dont really know.

off the cuff, i'm with sproggy, how does a small difference in ex back pressure overcome the magnitude of increased resistance from a closed throttle?

a high idle was always a poor mans slipper clutch. how would that overcome the backpressure?

oops just noticed your second post, i didnt know you were a tuner.

Brass
06-26-2008, 11:27 AM
I don't know either, try chopping the throttle on a big inch Harley motor with straight pipes, no back pressure at all there and it will do the same thing as it would with the factory pipes.

It is true that adding back pressure will slow a motor down faster. Almost all transport trucks have an engine brake. But that's adding an extreme amount of back pressure since they use a valve to close the exhaust port completely.

As I understand it (not claiming to be an expert, this is just my understanding of physics) the dynamic braking or compression braking, decel drag or whatever term you use to describe it, happens in the cylinder. Keep in mind the motor is an air pump. It was being supplied fuel that is being burnt and expands creating volume, when that fuel supply is cut, there is also less burnt exhaust gasses (volume) in the cylinder. Now there is less volume in the cylinder but the rotating mass of the motor is trying to keep that piston moving down the bore. This causes a pressure differential (partial vacuum within the cylinder) that tries to keep the piston from traveling all the way down. This is happening on the combustion stroke, when the intake and exhaust valves are closed.
It’s no different than turning a glass upside down in a sink full of water and trying to pull it up, it doesn’t want to rise, but add some air, fuel and a spark….. different outcome, the glass will leave the sink.

Try it out on your lawn mower. Disconnect the spark plug wire and slowly turn the motor over until it’s at top dead center on the combustion stroke. Then quickly turn the motor over just a fraction (less than 180 degrees). It will try to “pull” itself back towards TDC.

Just my opinion.