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I've a ZXR 400 l4. I recently changed the air filter to a K&N one, the old was completely shot and disintegrating into the air box. I took the carbs off and completely stripped and cleaned them. I set the float to 11mm but this chocked the bike and made it miss fire at high revs, about 8k. I've now changed the heights to 13mm but I've still lost a load of power. It doesn't seem to misfire but losses power at 10k revs and struggles at 100mph.
Do I need to increase the float bowl heights more? When I stripped it they were set at about 12-13mm.

you have increased top end airflow, switch to larger main jets.

simple, thank you. do you have any recomendations?

i would go up 2 step sizes (i.e. if you have #100's, go to #105's) and see if that makes a difference.

you can pre-test this by seeing if opening the choke when riding hard makes the bike pull better, if so you are lean at the top end and need bigger jets.

cheers. im a bit of a novice, its my first carb strip and tune. my understanding is the main jet is in 2 pieces and all i need to change is the top bit that picks up the fuel and sits inside the float bowl?? also what would shimming the neddle do? i was reading through some other posts and that came up. cheers once again.

6K1RKYJ9 wrote:cheers. im a bit of a novice, its my first carb strip and tune. my understanding is the main jet is in 2 pieces and all i need to change is the top bit that picks up the fuel and sits inside the float bowl?? also what would shimming the neddle do? i was reading through some other posts and that came up. cheers once again.

thats correct, the lower part of the jet is the emulsion tube - you cant change this unless you are going to lathe them yourself.

shimming the needle richens the mid-range, so 1/2 - 3/4 throttle, bigger main jets will richen top end, so 3/4 throttle onwards. you need 0.5mm M3 washers...ebay, get hundreds for pennies.

first get the pilots sorted and balance the carbs before anything else, then get on the bike and your looking for throttle position, not rpm! remember that. you need to see if you need more or less gas at 1/2-3/4 throttle, if so go back and shim the needle jet upwards with 1-3 shims - go back out and test, see if it needs more or less shimming. then when your pilots and midrange are sorted see if you need bigger mains (your midrange might have sorted it out a little by now), if so put in bigger jets and go from there...tuning is about feel if doing it on the roads. or you can pay for a dyno guy to do it, but expect ~£200 for them to sort it.

Sorry to be a complete noob again. I think my pilots are sweet, it starts most times first crack and idles fine, sometimes needs a little choke. She seems to pull fine in mid range. i think i get what you mean by throtle position and i think i could do with a shim on the needle. i assume when you say needle jet its the needle inbetween the slider and the diaphram? ill you tube how to ballance them i think i can manage that. do you know of a good seller on ebay for main jets? thanks.

Yeah, the needle that sits in the throttle slide, try http://www.motorcycleproducts.co.uk/cat ... 8_423.html for main jets and there is a guide on here on how to balance your carbs

I upgraded to 102.5 but they are longer then the 95's, the threads are the same it's the part that sits outside of the emulsion tube is longer. Is that normal?

perfectly fine

I'm having a complete mate with this. K&N filter with the 102.5's in, no shims yet. She starts fine, idles fine, responds ok and revs up fine. However when riding, in gear clutch out, I have no power and no acceleration and she drops off but doesn't stall. When I pull the clutch and free wheel she will rev up but not in gear. What am I doing wrong?

102.5's might be too much then, did you do the choke test like i asked before, i.e. when accelerating, pull in the choke and see if it pulls harder or not?

yep done that and it did make an improvement.

OK she mustn't of liked me yesterday, maybe the jets needed "broken in", a bit of crap stuck some where, water who knows. took her a run and shes pulling like a train when at full temperature, i didn't go too fast as had no leathers on. i had to open the choke up when accelerating through the mid range but that wasn't at full temp. ill take it out again and see if its sorted it out top end. still a little hick-up mid range.

Oh i forgot to mention there's a Micron system on her too, probably a massively important bit of info.

few shims on the needles then.