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damunk

engine running lean at IDLE

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damunk

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 there ran 13 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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kwijibo_coupe

Correct me if I'm wrong (probably am as I'm still new to bike carbs myself) but don't these have an idle jet and a main jet?

So really the fact you're using 150 main jets shouldn't make a difference to the AFR at idle?

 

I'd say you're maybe maxing out the idle jet now you're using carbs designed for a 600cc engine on a 1600cc engine? That is just a random guess stab in the dark though.

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damunk

sure bogg brothers set it up right for the 1400cc. im only certain they drilled 150 jets,

i just checked some old threads in the "bike carb setup" faq and theres a post of mine saying the 1400cc was idling at 11 AFR. so must have been running rich back then on idle also.

so changing from 1400cc to 1600cc makes that much different on idle?

Edited by damunk

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kwijibo_coupe

Like I say, it's only a guess but I'm pretty sure the main jets don't come in to play until you're up the rev range a bit. 

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damunk

is the bottom screw you can find underneath each carb on the cbr600 f4 the idle screw mixture?

i alwayss thought it was the main jet/fuel mixture

Edited by damunk

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dvderlm

 

 

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dvderlm

14% more air sucked through on 1600 versus 1400.

On a Weber I'd go up 0.05 but Webers don't have tapered needle of bike slide carbs..

 

Bikes idle much higher usually.

You might find the CBR600 choke size limits your high rev ability. That might not matter at all - depends on torque curve and gearbox.

It should pull well at lower to mid ranges.

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damunk

that link to the video you posted is for raising/lowing the idle.

 

im talking about those 4 screws at the bottom. one  under each of the carbs.

 

i thought it was the main jet but was wrong. someone told me it was the screw for idle mixture

 

and on most forums it refers it to just "fuel mixture."

 

14% more air. i think i might turn those screws half a turn anti clockwise.

 

 

 

 

 

 

 

Edited by damunk

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dvderlm

Okay, sorry,  idle speed screw, versus mixture strength screws.

Speed screw will open all 4 flaps same amount at nearly closed position.

Mixture screws let more fuel in.

Some cylinders are more efficient, often those nearest the coolant pump.

 

You've got the AFR gauge to tell you when it is right overall. 

Do you have anything to ensure all cylinders are equal flow?

 

 

 

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damunk

i have nothing to show all cylinders are equal apart from the fact the carbs originally were;;

A) set up by bogg brothers

B) all sparks plug ends are same colour and were same colour on old setup

 

Then have the AEM air fuel ratio gauge to show my reading.

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dvderlm

Spark plugs same colour is good. If turn screws same amount should be fine. 

If one plug was white and it was 17:1 I'd be concerned about a leak.

 

Edited by dvderlm

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caretakerplus

I am NOT familiar with the CRB 600 carbs, but have set up dozens of multi-carb engines using nothing more than a length of plastic hose placed in the ear and the other end held close to the air intake to each carb. The idea being to adjust the THROTTLE opening (NOT the mixture) of each carb to give the same sound in the ear from each one.

I have also used flow meters to do the same job, but generally revert to the plastic tube in the end.

 

The colour of the spark plug insulators is a good indication of mixture strength. 'Colour Tune' is a good aid, but doesn't lend itself too well to recessed spark plugs.

 

If there is a 'balance pipe' between the carburettors, you can run the engine at idle speed, closing down the THROTTLES on all but one cylinder, then set the MIXTURE to give the best idle. Move on to the next carb and repeat this, running the engine on one carb at a time until all carb MIXTURES have been set.

 

It is only once that the mixtures have all been set correctly that you move on to balance the throttle openings, using said plastic pipe.

 

A  VERY slight 'tweak' of the mixture might be required once the engine is running on all carbs.

 

I hope that this is not too basic, and is of some help.

 

Regards.

 

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dvderlm

Could you do the one cylinder at a time mixture adjust by removing three spark plug leads? I'm thinking of twin-carbs where two throttle plates act in unison per carb, one barrel per cylinder.

 

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caretakerplus

This is not something that I would do or recommend - engines don't take kindly to running on one cylinder.

You also have to remember that the exhaust gas leaving the engine has an effect on the incoming charge - Also with three plug leads off, you would be filling the exhaust system with petrol vapour, which could ignite and cause major problems.

 

Regards

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