engine stall coming off hard acceleration

[christianzx6]

I ran a search and nothing came up, so sorry if this has been asked a few times.

Basically coming off hard acceleration, pulling in the clutch and braking, seems to kill the engine, why would it do this, the bike idles great, runs aight, and accelerates hard enough to bring the front off the ground (its a zx6r 2000 model), but if i back right off, it just dies instantly, hard to notice exactly when, cos im normally focussing on bringing the front down as straight as possible or braking hard for the next corner or something. Im gonna be getting a jet kit and advancer as soon as i have the cash, cos at the moment i think the bikes getting more air than it should under heavy acceleration. I have a full yoshi and a bmc race filter. Carbs are all perfectly balanced, and i've tuned the idle mixtures as best i can for the jets that are in there. I've also got the needles to the richest setting, as it was pulsing really badly (accelerates then slows, accel then slow) with constant throttle, I assumed this to be a needle jet issue, cos it was in the needle rpm range of influence. I checked the fuel lines for kinks, and all the hoses are in good condition.

Important to note that this dosent happen when revving the bike in neutral, only under load.

thanks for any help

[Rossi]

Basically coming off hard acceleration, pulling in the clutch and braking,

You should not be pulling in the clutch mate, engine braking helps greatly in reducing your speed.........in an emergency braking situation I have been known to stall the bugger
I think whaqt you'll find is by having the needles set rich you are flooding the engine

[bonester]

Idle set slightly low?

[christianzx6]

Ok i'll try leaning out the needles, the idle's set to the manual spec (1300 rpm) i have mine about 1400 already. Engine braking i deem to be insignificant, and was taught to emergency brake by taking drive from the rear wheel and using both brakes. I find this works good for me, also worth noting is that engine braking on a 600 aint all that powerful, im assuming cos its a 4 cylinder makes it less suited also?

thanks for the advice, i'll get back to u with results.

[robracer]

2 strokes dont use engine braking that well..... but 4 strokes do & its not related to engine capacity either, so any size bike can use compression braking.

[MiG]

Basically coming off hard acceleration, pulling in the clutch and braking,

You should not be pulling in the clutch mate, engine braking helps greatly in reducing your speed.........in an emergency braking situation I have been known to stall the bugger
I think whaqt you'll find is by having the needles set rich you are flooding the engine

The rear brake can more than compensate for lack of engine braking. Whether it's harder to do or not is another matter.

[Rossi]

Basically coming off hard acceleration, pulling in the clutch and braking,

You should not be pulling in the clutch mate, engine braking helps greatly in reducing your speed.........in an emergency braking situation I have been known to stall the bugger
I think whaqt you'll find is by having the needles set rich you are flooding the engine

The rear brake can more than compensate for lack of engine braking. Whether it's harder to do or not is another matter.

Who's been teaching you guys ??
Under "emergency" braking the back wheel should be off the floor

[RG]

I suspect that it has got something to do with air intake

[christianzx6]

yeah well i dont emergency brake when coming down from a mono... not normally. But as this threads about braking now, i think that the rears good for most braking situations, under extreme braking, the rear will easily slide, and its normally better IMO to use only the front if the rear locks, so that u can release the front then dodge whatever it is ur braking for. Best not to let the rear snake outta control.

RG, what makes u think its an air problem, the intakes are all clear anyway, just so you know, as stated its flowing lots more air than stock (BMC race filter, full yoshi system), but still running stock jets/needles etc. Also this only happens at high(ish) speeds, of 70+kph, where there is significant airflow. Also as the needles were set to richest, i backed them off 1.5 spaces, have yet to test ride cos im working on getting my keyless ignition to work on my alarm system, its proving to be awkward. Trying to use a relay to recreate the conditions of the key ignition, thinking there might be something mroe fancy than a couple of switches and a resistor in there.

[Neilp]

If you have replaced stock exhaust and changed air filters it is time to spend the money and get the bike dynoed and have a jet kit fitted.


Neil

[Gosling1]

Good advice that. You will spend a lot less time tuning it on a dyno, its worth the money.

[mike-s]

+2, agreed. You'll know exactly what the bike is doing, and where it's doing it. None of this "guesswork" malarkey

[christianzx6]

whilst i agree with you, funding at the moment is an issue, and i'd rather tune it myself and get braided lines than pay someone with a dyno to do it.

factory pro has a detailed but straightforward tuning guide, and as a bonus i love to do this stuff myself anyway.

If i had the money i'd buy the kit now, and see if it fixed the problems im having.

I backed the needles off 1.5 spaces and it ran crap, jolting was happening at low speed lower rpm, 4-6. I fanged it a little (probably went up to about 10-11thou) then pulled the clutch in to see if it'd die, it did. So it didnt fix the engine cutout at high speed and it made the midrange unusable. so i took it back to the garage and set the needles back to max richness.

Set the needles back to max:

The bike still sometimes behaves like its starved for fuel, was on the freeway cruising and it started to jolt again, closing the throttle slightly sped the bike up and smoothed it out, but only for a short time (2 seconds max). This is why i think its a too much air, not enough fuel problem. When i closed down the butterfly's, the bike came to life and stopped its bucking.im tempted to restrict airflow and see if it improves performance. The bike runs better at low speeds, the jolting gets annoying, and its gonna trash my chain if it continues, not to mention its probably not great for any part of the bike at all anyway.

im running BP ultimate fuel, so its not a pinging problem, there's also no ignition advance on it (besides what the ignitor puts on).

Could the jolting have anything to do with the diaphragms? it does seem to happen in the needle circuit range (4000-7000 rpm). The reason i ask this is because i cleaned my carbs with carb cleaner on the bike, to try and suck the crap thru (u put ur hand over the venturi and the vacuum pulls the carb cleaner thru it). well anyway, 2 of the diaphragm's have gone sorta wobbly looking, they dont have the strict form of the others, they still seat right, have no tears etc, but have a 'warble' in them. hard to describe, imagine the good ones are ballons which have not been blown up (smooth sleek rubber), and the bad ones have that affect ballons get when they have been blown up and then realeased, sorta a ripple on them. Well thats the effect 2 of my diapragms have, they still good?

Also does anyone think increasing the level of fuel in my floatbowls is a good idea, im leaning towards it because i wont be able to order a jet kit for at least 2 weeks.

and just back on tuning, to those who havent tuned at all, its fun and addictive, maybe they have group sessions i could goto, and come to terms with my tinkering addiction.

[mike-s]

well increasing the fuel level of the float bowls messes with the *just* off idle performance. If it picks up off a closed throttle without much in the way of hessitation or snatchiness, it may be right in that department.

the rolling the throttle off a few degrees and the "2 secs of goodness" indicates to me that you may be too rich somewhere, then again too rich is easy to diagnose as the engine starts operating choppily, too lean is a bit harder as until you hit way too lean, its just going to act a bit funny (in my experience).

If the bikes *REALLY* stuttering and staggering, that indicates a too-rich problem at that point in the circuit.

What you NEED to do is to mark the switchblock next to your throttle with the throttle openings. and put a marker on the right grip accordingly.

WOT -- 3/4 -- 1/2 -- 1/4 -- 1/8 -- 1/16 -- C (losed), this will tell you what circuit your (primarily) dealing with (remember every circuit messes with the settings of those either side of it to some degree). This will remove the guesswork as to which circuit you'll be messing with.

The symptoms your describing do sound like "too much air", but with it only occuring when the throttles roll shut makes me wonder. Have you checked the emulsion tubes for out of roundness? they could be out and would naturally totally throw your tuning out the window (near impossible to fix by tuning around the problem, the bastards have to be replaced).

[christianzx6]

the bike is stuttering and staggering badly, well it was until i richened up thte needles, then it got a lot better at low speed. This is why i think its a lack of fuel flow problem. If you think the stuttering and jolting is a too rich problem, i'll try leaning the needles right out. im pretty sure its the needle circuit, but i'll check the throttle positioning too.

basically i need a jetkit to sort this all out. i just want to get it rideable until i can afford one.