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Author: Subject: running lean on idle
bikecarbfred

posted on 2/3/19 at 11:26 PM Reply With Quote
running lean on idle

cbr600 carbs were set up by bogg brothers on my 1.4 afh setup. they ran rich because was using 150 jets.

so at idle they ran 12-13 AFR and at 2000rpm in stationory position AFR was around 13.0- to 14.0



but using the same carbs on my 1.6 afh conversion setup they run lean on idle

idle was over 17 when engine cold causing exhaust to sometimes make like a spitting noise.

when warm , gets around 15.9 -16.0 ish





in stationary position revving it up to 2000rpm gets it where it should be 14.7, (when engine is warm)



i've done some research and timing shouldn't affect AFR significantly to get dodgy AFR readings.



theres a idle screw that controls where idle position is.. i increased that to around 1500 rpm to get a decent enough AFR to avoid damage.

i took off the brake vacumm hose and re-installed it to make sure it's dead tight. where else can there be air leak.



the jubilee clips around the intake manifold for holding the carbs are pretty crap. they are tight but if you overtighten these jubille clips the nut jumps , making you tighten it to a certain limit. but noticed tihs issue with old set up.



the only thing that is different apart from the engine lol, is that im doing the testing with no bonnet and no induction pipe and ram air filter

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Nickp

posted on 3/3/19 at 08:12 AM Reply With Quote
Have you not tried the idle mixture screws? They should be one underneath each carb. Mine are at 2.5 turns out (ZX6R carbs) and give a perfect 14.7:1.
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bikecarbfred

posted on 3/3/19 at 08:21 AM Reply With Quote
quote:
Originally posted by Nickp
Have you not tried the idle mixture screws? They should be one underneath each carb. Mine are at 2.5 turns out (ZX6R carbs) and give a perfect 14.7:1.


there's only one screw under the carbs. isnt that the main jet screw

think the other screws you have to open the bowl?

CBR600 1999 F4

[Edited on 3/3/19 by bikecarbfred]

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Nickp

posted on 3/3/19 at 08:45 AM Reply With Quote
The screw will be the idle mixture. Turning it out will richen the idle.
You open the bowls to access the main jet to either change it or drill it out as required, this only affects the top end.
You can also change the needle height by removing the carb lid and moving the clip in the grooves. Lowering the needle leans the mid range, raising it richens the mid range.

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bikecarbfred

posted on 3/3/19 at 09:33 AM Reply With Quote
well if that screw is the idle mixture then im sorted.
just turn it half a turn clock wise on each of them.

thought that was main jet or fuel mixture screw.

http://carbjetkits.com/jet-installation.html

[Edited on 3/3/19 by bikecarbfred]

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Nickp

posted on 3/3/19 at 09:37 AM Reply With Quote
quote:
Originally posted by bikecarbfred
well if that screw is the idle mixture then im sorted.
just turn it half a turn clock wise on each of them.


Anticlockwise (out) to riches.

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bikecarbfred

posted on 3/3/19 at 09:41 AM Reply With Quote
quote:
Originally posted by Nickp
quote:
Originally posted by bikecarbfred
well if that screw is the idle mixture then im sorted.
just turn it half a turn clock wise on each of them.


Anticlockwise (out) to riches.



thank you. so this is the fuel mixture screw and will affect idle and middle and top end?

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Nickp

posted on 3/3/19 at 09:45 AM Reply With Quote
quote:
Originally posted by bikecarbfred
quote:
Originally posted by Nickp
quote:
Originally posted by bikecarbfred
well if that screw is the idle mixture then im sorted.
just turn it half a turn clock wise on each of them.


Anticlockwise (out) to riches.



thank you. so this is the fuel mixture screw and will affect idle and middle and top end?


Purely idle. As I said above, needle height does mid range and main jet size does top end.

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bikecarbfred

posted on 3/3/19 at 09:54 AM Reply With Quote
surely this will do it. seems the 1.6 cuz of longer stroke is taking in more air on the idle
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