Carb Setup

[carsounds_dan]

hi,
basically i have a zxr400 with a full micro system, i dont think that the carbs have been setup for it though.
so can anybody give me any advice on carbs? jets? and all that sort of stuff? im going to have the engine out over winter, to change the camchain, tensioner and head-gasket as theyre all about due... so might as well make the most of it and do some fine tuning.
cheers
dan
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[Blau Zedong]

The local dyno is your friend.
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[bish777]

buy a few sets of jets the next few sizes up from stock and play with it.
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GSXR1100J

[TUG]

i'm thinking of doin this, bish, have you done this without a dyno?
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Haz ER-5, innit!

[bish777]

Its easy enough to do without a dyno, but it does take time and patience.

Its a black art of reading spark plugs, plug chopping and your inbuilt seat of the pants arse dyno.

You need to get the engine to this point.

1) nice mid to light brown plug at all rpm, as tested by plug chops.

2) no stuttering flat spots in power delivery

3) (in fours at least, with CV carbs) Should accept full throttle at low engine speeds and accellerate cleanly in any gear.


rough idea is to go up 2-3 jet sizes for a race exhaust, 4 for pod filters, 1-2 for a loud can on a stock system.

Fine tuning is done by adjusting the needle. Find the jet were the bike is happiest and finetune the delivery by adjusting the needle, this is how u rid the delivery of flatspots in the bottom/mid range.
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GSXR1100J

[TUG]

the problem i find with the colour of plugs is i have to drain my coolant to get to them, would a colourtune set not be better? when i had my micron can on i had it brown without dyno or anything, but since i changed the can i've reset it all over again.
i'd love to fine tune it so i get the best results and believe me i have the patients.
so what would you suggest, colour tune kit or go to long rode and get to max rpm and kit the kill switch?
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Haz ER-5, innit!

[bish777]

I have a gunson gastesterwhich is basically a very simple emissions tester that measures carbon monoxide output and this allows you adjust the mixture fairly accurately. Colourtunes only really allow the setting of the idle mixture-on seperate main and idle circuit carbs like fitted to most carbs means they arent terribly useful.

What you need to do is take the bike for a nice run to get it fully warm.

If you open the throttle, and the engine bogs down and/or shuts off entirely your mainjet is too small. If it stutters up into the midrange but pulls strongly at higher RPM your needle is set too lean and needs to be raised, or perhaps a slightly larger mainjet as well.

If the bike idles roughly, and doesnt want to rev cleanly, makes wet belching noises and/or throws out alot of black smoke (and possibly flames) out of the pipe then your set too rich.

Get up to 40 mph, put it in top and fully open the throttle. It should begine to accellerate without hesistation or stumbling ( i know it will be slow on a 400). If it does stumble it is probably lean and needs a larger mainjet.

Take it to the redline in every gear if you can and feel for any flat or rough spots. A 400 will be a little peaky but you should have any noticable flat spots. You can find out if the flat spots are lean or rich with plug chops (hit the kill switch at that RPM)
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GSXR1100J

[TUG]

with you saying that, my bike has an exup valve that gives me extreme midrange, at the moment i dont have it in, and where theres no midrange power my bike has a band at 10,000rpm.
the gas tester you have, is it easy to use? will this help me accuratly set the carbs up easier than taking it for a spin? also, my 6th gear is unusable, i'm hoping that this winter i can drop the engine out and fix my gears and selector and use a cg125 for hack, we'll see. thanks for the info so far you've cleared alot for me.
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Haz ER-5, innit!

[bish777]

The gastester helps you set your idle, and then allows you to check you have gotten in the right region with your mainjet and needle settings. Youll still need to take it out for a spin to make sure you have the best clip position.

Youll have fun tuning out flatspots without the EXUP valve as the cams are profiled to work in unison with it.
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GSXR1100J

[TUG]

damit.
looks like i'll have to live with the flat spot. am guna turn in my idle mixture aswell as my bike runs tooo cool.
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Haz ER-5, innit!