engine stall coming off hard acceleration

[Gosling1]

.....basically i need a jetkit to sort this all out....

thats *exactly* what you need, and when you get it, the additonal information in the jetting kit should at least give you a baseline to start from. It *may not* give you perfect jetting the first time around......

Its great fun to do things yourself, and I hope you get it sorted. But good jetting can take ages, its way simpler to tune it on the dyno, you can then be out riding and enjoying the benefits of the better exhaust, air-filters etc, instead of ripping the carbies on and off a hundred times.....

[mfzx6r]

My zx6r did that once till I found I had been riding with the choke full on for the last 50k's

[christianzx6]

i did actually try engaging the enrichener circuit whilst riding, it didnt buck real bad, but it wasnt right either, made the throttle less responsive. im not gonna ride around with the enrichener on anyway.

[mike-s]

oh and another thing to mention is i added a jetkit to my old bike. If you can get one, a factory pro jetkit is more recommended than the dynojet ones.

Common feedback i've seen on the net is that the latter run the bike *WAY* too rich. I put a stage one kit with the airbox mods in my gpx, and i was still getting an air/fuel ratio of 10.5>11 :1 at its LEANEST. Ended up buyin oem jets and throwing them in. 3/4 the reason to buy a jet kit is for the aftermarket springs and needle. the jets are merely a formality.

and i'll reiterate again, check your emulsion tubes, if they are out, it *WILL* fuck with your fueling quite badly. they only have to be out by 1/10th of a mm to cause fueling problems.

[christianzx6]

im ordering a jet kit today, do jet kits come with emulsion tubes? also how the hell do i know the original size? there's noway i can measure that accurately externally let alone internally. I think i'll assume they're fine until i've got the jet kit and finished tuning as with that and the ignition advance. Im hoping/praying that the jet kit is going to solve all my fueling problems.

And yeah, i'll be getting a factory jet kit and +4deg advance, as per the advice of people in the dyno thread in this section.

[RG]

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).

Chris, That was exactly what I suspected, only that I don't know how to put it across in words.

[balanse]

Chris the solution to your issue is richer (larger) pilot jets. It's a classic scenario that you describe and well trod by many. Your pilot jetting has gone from factory lean (to pass emmision testing) to factory lean plus aftermarket parts (even leaner at low throttle opening carburation). The bike is unable to deliver enough fuel at low throttle to keep the motor running comfortably.

If you want to solve this then identify your current pilot jet size (usually means you have to open the carbs and have a look) and buy some pilot jets one and two sizes up. Unfortunately the downside of jetting is that it takes trial and error - there is no magic formula, just a bit of repetitive work.

Fit the first size - might fix everything, if not then try the next larger. Your problems WILL resolve as your jetting becomes more accurate.

Admire your DIY attitude too - good stuff.

[rotaboy]

this may be a stupid response but are the carbs balanced properly?

[christianzx6]

the only stupid question is the question not asked, except in this case, when i said 'the carbs are perfectly balanced' in my first post

[rotaboy]

may bad that will teach me for not paying attention properly

[mike-s]

a fair few bikes dont have fixed pilot jets, just a tube that sucks fuel into the carby. You merely have to adjust the tuning of the pilot needle, dynojet specify 3 turns out as a good starting point, i eventually got mine down to 2.5 by friggin with it and finding what worked/diddnt..

seriousll though, just find out the part numbers of the emulsion tubes and just replace the farkers, you'll be no worse off, except about $120-160 poorer ($30-40 EACH ) and its impossible to tell if it makes a difference until you replace them. oh and r.e. measuring them, you need to take the carbies apart, the emulsion tubes sit up under the main jet, so floatbowl off, main jet out, emulsion tube out, etc.

[christianzx6]

yeah i know what the emulsion tubes are, but i have noway of measuring them, i dont have a micrometer that goes internal... hell i dont even have a micrometer. What I do have is a factory pro jet kit and +4 ignition advance rotor headed my way from the good ol US of A and should get here by the end of next week.

I have already tuned the pilot jet needles (aka mixture screws), and it didnt just whack them all to the same, i carefully listened to the engine and looked at the tacho closely until i got max rpm at idle, then did the same thing on the others, twice. What i did was set idle rpm to 1000, making it easy to see slight increases in rpm. Then once i had the max rpm i could get outta that screw, i lowered the idle back to 1000 on all of them, and went along the row. So the pilot jets are tuned. Basically no movement here until the jetkit and advancer arrive, then this thread will become a hive of activity again!

[balanse]

Pilot jet and air screw are not the same and offer different jetting outcomes.
Air screw allows air into the pilot circuit but is only able to alter carburation by the sizing of the pilot jet in the carb.

[christianzx6]

have spent a day and a half working with the jet kit and advancer, and its not only sorted out the flat spots, but has made the bike insane fun to ride. Ended up with 160 1/4 162.5 2/3, richest settings on the needles without using the spacer (5th slot down), 9mm float height and 2.5 turns on the mixture screws.

the bike really goes from 7.5K onwards, but pulls well (the best i could get it) from 2.5-3k. Not a massive jump at 7, like there was when i first got the main jets right, with leaner needle settings.

Front wheel defies gravity in first and second when rolling on, doubt it'd do it in third. Im over the bars trying to keep the wheel down when i gun it, the adrenaline rush is awesome, so much better than my poor old rgv.

Also as an aside, I softened my suspension and reduced the preload on the front forks quite a lot from standard (which is for a 68kg rider). Well im 72-74, so i figured standard would suit me pretty good, but it dosent, too many bumps come through, distracting me when im focusing on my line or looking out for pc plod.

What sort of suspension settings do you guys use for spirited riding, how much front dive is normal under heavy braking, do you want front dive etc? where i reduced the preload, i've noticed the front dives a little more than before, it used to feel like it hardly moved at all. I prefer to feel it dive, but thats because thats what my rgv does, which im used to riding. How much dive is normal? I might just try a few endo's, if it feels like the front is sinking into sand i'll increase the preload. hints suggestions tips?