www.zxrworld.co.uk

HI all
Im new here having just having bought a tidy 92(import) ZXR400 L1 ...really liking the bike despite it being a big step down it terms of grunt from my VTR, much nicer handling though and more suited to my shortass height

Anyhows bike has a K&n filter and Full Beet TI headers and can (road legal i guess as its not loud) it has supposedly been 'setup' up on a dyno by previous owner but it doesnt feel like it to me!...it revs well enough but feels like its lean in midrange as doesnt like larger throttle openings less than 10k with a flatspot between 8-10k....also once your up into proper power (above 10.5k) it takes awhile to pull again when you change up at 14k despite it staying in powerband on rev counter!.....i could live with flatspot as you can drive around that but once up in power its annoying to have it go flat for a second after changing up despite revs being above 10k.

Going to pull plugs and check colour and also carbs off to see what jets/float heights etc it had in there but wondered if any of you guys could give me a pointer on what sort jets etc i should start with with these mods to bike ?

Ive previously fitted a dynojet stage1 to my VTR which fixed a similar issue after fitting freeflow airfilter and race microns so was thinking of doing same on ZXR but at price of them it would be nice to avoid it if i can, just up main jets or something to smooth it out and sharpen things up.

Any input welcome

Cheers
Ian

OK stripped carbs off bike tonight and found it has what looks like stock jetting although they are odd sizes!.... inner jets are 90 and outer jets are 88!...also carbs look like 30mm not 32mm I was exepecting, any ideas guys ?

Is ti worth getting some 32mm carbs and rubbers ?

Cheers
Ian

i dont know dude,but i hope some one round here can help you soon

zxr500man wrote:i dont know dude,but i hope some one round here can help you soon

Me too!

Ive just stripped the needles out to see if they are the stepped ZX4 needles ive read about but they arent, also found a couple of shims on them so does look like its been apart at some point, was beginning to wonder if the so called "setup on dyno" i was told had actually happened!....so far evidence points to a quick temp fuelling fix by shimming needles but leaving jets small, certainly doesnt seem to be getting enough fuel in to me, maybe it was done before k&n went in and hasnt been rejetted to suite!...i know my more or less stock ZX4 pulled a lot nicer through the revs many years ago.

Im wondering wether to bother playing with jetting on these 31mm carbs and if so how far up to go....was thinking of getting a pack of 92.5 and 95 and trying a few different options, maybe stay staggered and up 88's to 92.5 and 90's upto 95's .....anyone any input pleaaaasssse

Cheers
Ian

I would junk the 30mm carbs get some 32mm ones and head to a dyno its the only way to get the fueling good.As with out an air/fuel meter your just guessing.I have a set of 32mm carbs here if you need them.

Robbie wrote:I would junk the 30mm carbs get some 32mm ones and head to a dyno its the only way to get the fueling good.As with out an air/fuel meter your just guessing.I have a set of 32mm carbs here if you need them.

I was thinking about that but wondered how good the 31mm carbs will be if jetted correctly , im not after wringing every last hp out of the bike just making it more tractable and getting it to run right, I would be suprised if there is a huge difference between the two sizes of carb unless you have info on this ? ....bigger isnt always better i find as i know on my previous RVF400 it ran best on the RVF smaller carbs than larger VFR400 carbs, i beleive it was possible to get more outright power on larger carbs with a lot of dyno time, but driveability wise the smaller carbs were much easier to sort....of course I know the ZXR is a totally different setup but would of thought if factory fitted the 31mm carbs they should be able to get a decent tune with them....or have you heard otherwise from your comments ?

I do have an good wideband airflow meter from my car tuning experience so should be able to get a reasonable idea of whats going on and then fine tune on dyno if required.

Im going to try upping main jets i mention above but if i dont have any joy i will be in touch about your 32mm carbs, do you have the mounting rubbers for them as well ?

Cheers
IAn

the 30mm carbs will work fine, and its easier to get a smooth midrange with them, but the topend will be down by a touch.

with your setup, there's two ways forward really,

1) keep the KnN, shim the needles up a touch, fit ~#102 mains and remove the snorkel from the airbox**

this is basically how my L4 import (with 30mm carbs) was setup ( i had #105 mains and a micron exhaust, it was a bit rich at the top, but even richer when i fitted the beet which fueled better than the micron and preferred slightly smaller jet sizes

2) bin the KnN, fit a stock filter, shim the needles up a touch, fit #95-#98 mains and keep the snorkel in place.


**the KnN only pulls air from its sides, the intake snorkel presses up against the filter's plastic front face.. this restricts the airflow. For this reason i dont like them on L models as ultimately the fueling is smoother with the snorkel in place.

get the main jet size sorted first then worry about correcting the midrange 8-10k flatspot

dynojet needles may help.. but they are designed for the 32 mm carb bodies.

zimm wrote:the 30mm carbs will work fine, and its easier to get a smooth midrange with them, but the topend will be down by a touch.

with your setup, there's two ways forward really,

1) keep the KnN, shim the needles up a touch, fit ~#102 mains and remove the snorkel from the airbox**

this is basically how my L4 import (with 30mm carbs) was setup ( i had #105 mains and a micron exhaust, it was a bit rich at the top, but even richer when i fitted the beet which fueled better than the micron and preferred slightly smaller jet sizes

2) bin the KnN, fit a stock filter, shim the needles up a touch, fit #95-#98 mains and keep the snorkel in place.


**the KnN only pulls air from its sides, the intake snorkel presses up against the filter's plastic front face.. this restricts the airflow. For this reason i dont like them on L models as ultimately the fueling is smoother with the snorkel in place.

get the main jet size sorted first then worry about correcting the midrange 8-10k flatspot

dynojet needles may help.. but they are designed for the 32 mm carb bodies.

Thanks for the info Zimm

So you think I should go straight up to 102 mains from the 88/90's that are in there at the moment ?... needles already have approx 1mm of shimming under them, was thinking of removing these once bigger jets are fitted to see how it performs, maybe not a good idea ?
Also i was wondering about the k&n and snorkel, as you say snork presses onto filter body but couldnt see how this would be any more restricive than a stock filter as its probably larger surface area of filter on k&n due to it being deeper ? was thinking snorkel entry size might be a restriction though.

I ordered the 92.5 and 95 mains earlier today as was trying to get something here so I can have a play about with at weekend, guess i will try those first and see how it goes and report back, next question being wether to stay with the stagged jets or just go same across all 4 ?

All input welcome

Cheers
Ian

how much the needles need shimming kinda depends on which needles they are .. (there's several types been fitted as OE for different model years/markets - the longest i've seen were N770, which are a good 2mm or so longer than some others) but the needles shouldnt really be affecting the topend as the slides are all the way up by then anyway...

so i'd probably decide on what you want to do about the intake (KnN/snorkel/OE etc) then find a main jet that works with what you've chosen and gives you crisp running from 10k to redline, then iron out the midrange with needle heights (or different needles)


stick the same jets in across all 4, once its all sweet you could try staggering the jets again by going up one size on #2 and #3.

btw, dont expect it to feel as nice up top as your old ZX400G.. different cams, airbox etc .. both my ZX-4's blew the proverbial doors off my zxr's.... even my ex girlfriends 60,000 mile shitter would keep up with my racebike and dyno'd at only 4bhp less and my L4 never stood a chance against it on open roads

OK jets came today so ive had a play with what i had here, put the 95's in all 4 carbs, left 2 shims on needles and the k&n and snorkel fitted, refitted it all and balanced carbs up so now ready to testride just need it to stop pouring down and I can go for a blast!, inital impression from a very quick blast up and down estate in 1st with wot pulls from 3k to about 9k (before room runs out!) and it seems no worse.... so i guess thats a start.

Needles i checked and are marked what looks like N77Q or could be N77O i guess, bad to make out, does this mean anything to you zimm ?

Cheers
Ian

Finally got chance to take it out for a good run today with 70miles of various roads, feels a better everywhere in the revs with good smooth power from 6k up.....still a little flatter than i would like but I am trying to remember what a well setup 400 goes like so maybe expecting too much ....think i can still improve things though and havent had chance to rig the A/F meter up yet to check fueling numbers but think maybe still a little lean, I just tried it after removing snorkle and would hardly pull above 8k! hence thinking still a little lean, making it very lean with snorkle removed, or am i barking up worng tree ?

Not sure what to try next, I guess its either go back to stock air filter or try bigger jets....will try and rig the wideband a/f meter up and go for a run to see exactly what fuelling is doing if i can.

Cheers
Ian

Ok thinkim going to try a stock filter next, anyone got one they can sell me ?....ive put a wanted add in classifed and will keep an eye on ebay etc but wondered if anyone on here has one

Cheers
Ian

sounds like its moved in the right direction.

does still sound lean up top, (your logic re the snorkel removal affecting the mixture is correct)

I'd still be looking to increase the jet size in line with my previous post, and perhaps raise the needles another shim

N770 are quite long (lean) needles.

zimm wrote:sounds like its moved in the right direction.

does still sound lean up top, (your logic re the snorkel removal affecting the mixture is correct)

I'd still be looking to increase the jet size in line with my previous post, and perhaps raise the needles another shim

N770 are quite long (lean) needles.

Was thinking of getting some 98's in there although i was wondering if i put in a stock filter with snorkel will it be richer or leaner than the k&n with snorkel ?

Ive chance of a cheap dynojet kit and wondered if it was worth the hassle? as its designed for 32mm carbs etc, or just stick with what i have and some more fine tuning which doesnt seem far off now.

Cheers
Ian

thetyrant wrote: i was wondering if i put in a stock filter with snorkel will it be richer or leaner than the k&n with snorkel ?

I would expect with the snorkel fitted for it to be leaner with the OE filter

#98's sound about right with this setup, maybe even #100's

are your replacement jets keihin or dynojet ?