Carb set up (pilot mixture for hybrid motor)

[markzxr400l3]

hi all

I had it running quite well but there was a wiring problem so I got a new loom. While I was at it I set about the carbs as I felt they were running a bit rich at low rpms.

Long story short, been at it all day, thoroughly p1ssed off, manuals no good to me cause the bike is a frankenstien.

Can anyone help. Ive got an L model (L3 i think) so the pilot screw should be about 1 and a half turns out (right?) so I did this but the bike cut out at idle and wouldnt pick up properly (too rich?).

Then I realised I have no idea where the carbs came from (it came with three sets) so could be H, L or anything. I further realised that I have put zx4 cams and top end on it. Also I doubt this is the orignial engine so I'm possibly trying to set up a set of L carbs with a H engine with zx4 Cams. Oh and just to top it off, Its got a k&n air filter and a carbon can (just in case it was getting too easy).

My last attempt was 2 and a quarter turns on the pilot screws and it got about a hundred yards, cut out and would only start on full choke (way too lean?).

I think my main question is which way is lean and which way rich? I am assuming in is rich and out is lean? If thats the case I'm guessing about 1 and three quarters but is the bike really that sensitive?

All help/therapy appreciated.

[steve87]

start from fully turned in. screw out 1.5 turns. the further out you turn it, the icher it will be as more fuel will go through. get the engine running nice and hot, clean your plugs up ( maybe wire brush then end of them) AND THEN REV THE ENGINE, IF WHEN YOU OPEN THE THROTTLE, THE revs start to fall ( when you cloe the throttle quickly)) but sit at 2000 revs, fore falling back to 1300 revs, its too weak.
or take it to a dyno place. they will do thos all

[RedexRobB]

this sounds like one for zimm, standard settings are 2 and a 1/4 turns out from fully in. Might wanna check the main jets in the carbs for the size. standard is #88, #90, #90 and #88 iirc. Cam profiles i think are different on the ZX4 so thats bound to mess with fueling. You need not bother with the K&N the standard filter is just as good too.

[zimm]

what airbox are you using ? ZX4 ? H ? or L ?..

afaik pilot jet sizes and settings are the same across the board (2.5 turns out.. ish)

if you are using zx4 cams you really need zx4 needles or dynojet ones, they are both stepped rather than a smooth taper like zxr ones, and preferably zx4 emulsion tubes as the cross-drilling varies and better suits the needles (and airbox characteristics). This should work fine with an H model airbox with either pipercross or OE air filter. Main jet size depends on the exhaust used, .. ~#95-98 if stock upto maybe #102-#105 with a full system and noisy can.

not sure how an L airbox would change the airflow, but lets assume its a bit more restrictive as the L model jetting is more conservative.

have you removed the intake snorkel from the airbox ? if not the KnN will be flowing worse than OE. My L4 had 32mm carbs, #105 mains dynojet needles, KnN and the snorkel removed + full micron system.

our ZX4 has H carbs (32mm) #98 mains, ZX4 needles, H airbox, ZX4 cams.. its a bit rich in both the midrange and topend.

[markzxr400l3]

Cheers guys,

I'm at just over 2 and a half turns out now and its a little lean (characteristic is slight 'hanging' of revs). I'm going to set em at 2 and a half and balance them up.

Confession time!! When the bike cut out I started to strip it down and found that the fuel switch was off. What an idiot!!
I think I've got a short fuel switch (i.e. the switch sits too deep in the recess) so I cant turn it without stripping it down. I'd obviously forgot to set it to 'on' before taking it out for a test.

What a donkey!

Zimm, your a genius mate, and your knowledge is vast. I got a set of zx4 carbs that might be a little gunked in the float bowls, I presume I can just pop the tops off em and drop em in diaphram, tube and needle as a whole unit. All sounds good.

Bike is running okay now. I will take the advice and remove the snorkel as I've got an L airbox on it at the mo with a k&n. Ive got a H airbox lying around, does that fit okay under the L tank? be nice to make sure its breathing as best it can.

I will invest in some dyno time come next spring I think and just get it spot on.

Cheers all, I know where I'm going now.

[zimm]

the slides dont swap from ZX4 to H/L carbs, they look like they should but dont open fully (dont go all the way up)

just swap the needles and the emulsion tubes from the ZX4 carbs to the ones you are using.. and measure the width of the throat of the carb at the cylinder head side.. you want some that are 32mm. some L's arent, they are 30(ish) which is the same as the original ZX4 carbs*. Inlet stubs should also be 32's to match the carbs.

time on a dyno will get it spot on, but this is what worked when putting 32mm carbs (from an H1) on our zx4.. tried several sets of needles and emulsion tubes (H1, H2, L4, Dynojet, ZX4) trying to get smooth power delivery, (aswell as H and ZX4 airboxes) and it always came back to the zx4 needles and emulsion tubes combined with the H airbox, ZX4 airbox made the topend rush feel awesome, but only because the midrange was less. No idea if H airbox will fit under an L tank .. probably not. L box should be ok though, and at least the bellmouth design is better.

bear in mind that ZX4 cams are essentially non-adjustable SP cams, and you'll have an idea which way to lean with setup.

*which arent a straight bolt on as the bracket for the cables is different... n stuff.

[markzxr400l3]

Thanks Zimm,

Finally got round to taking your advice today with the two sets of carbs and it really makes a difference. Not quite there yet though and wondering if you have just a little more advice.

I put the emulsion tubes and needles from the 30mm ZX4 carbs in the H carb bodies, set the idle screws at about 2 turns and installed, I balanced the carbs and let her rip. (BTW is there any way of balancing the carbs with the air filter on? - seems to me that if you balance them while the mix is lean - no airbox - this gives a false setup??)

To start with when warmed up the revs would hang when coming down and any touch of the throttle just made the engine die, to cure this I now have the idle mixture screws about 3 and a quarter turns out which seems way rich to me but seemed to have solved the problem. I was just wondering if changing the pilot jets might help?

Other than that its smooth and crisp all the way up the scale but I can still make the engine cut out if I grab a big handfull of throttle from idle, the further out the idle screws the better this gets but at 3 and a quarter out I'm so far off stock already warning bells are ringing. I havent got her on the road yet as its wet (and my bike is clean LOL) so I cant say for sure how it runs in real life.

Dont get me wrong, its way better than I had it (thanks mate) but its just not quite there yet.

Any final tips?

Mark

[RedexRobB]

Not really any way to balance the carbs without the airbox since you wont be able to get to the balancing screws with it on. It should be fine since its the same way as the manual, all the balancing is doing is telling you the vacuum on each cylinder so they are all a the same runing speed, airbox on or off shouldnt affect it since the reading on the dials doesnt matter.

If the revs are hanging, then theres an air leak somewhere, check the airbox is fitted properly and also check the inlet rubbers, they are very prone to leaking on the ZXR. You can check them by spraying some carb cleaner round the inlets while the engine is running, if the revs change while you do this then theres more then likely a leak.

If you can sort that then you may even sort the engine dying on a the throttle.

HTH

RobB

[markzxr400l3]

Cheers,

I think its sorted. I had to turn the pilot screws out to 3 and a half but its now smooooooth all the way through the range and idles fine (although I left it for about 20 mins and it died eventually - but my rectifier isnt fitted at the mo as it self destructed so that cut out may just be low electrickery juice).

I have the #95 mains in but I've got a set of #102s that I might try to see if the top end gets any better. At the moment off the throttle in first the front is going pretty light so I reckon thats pretty good for a 400, certainly has more kick than my old FZR 400.

BTW careful out there guys (& girls), its icy as feck!! a coupe of my mates have binned it in the last couple of days.

Cheers.

[zxr500man]

Hi Mark,

I am in the process of putting zx4 cams in my zxr 400 h,

So its just the needles from the zx4 and the rubbers, with a h air box?

Also i noticed the zx4 needles have n77 engraved and my h ones have n36, but the both look identical ?

Thanks for any tips.

[markzxr400l3]

Sorry ZXR500man. I've been away a while (playing at being a lunatic on a GSXR750). Genuinely cant remember now - at that stuff was three years ago now. Sorry Dude. I do remember the cams are definately worth the hassle, it went like a bomb after 10k revs.