Main Air Jets

[mick41zxr]

Ok mods may want to move this
Fo CV carbs the main air circuit has a pressed in main air jet.
This can be removed & made interchangeable as per FCR's
Keihin 393 series jets in #50 through to #200 can be used, photo of removed air jet and a 393 series jet below.

jets.JPG

[mick41zxr]

Location of Main Air Jet shown below,

carb1a.JPG

Pull the existing pressed in main air jets out with an ezy out & tap the hole m5 x 0.8.
Remember to hold the carbs upside down when when drilling & tapping to prevent swarf from blocking the carb.

carb2.JPG

Interchangeable Main Air Jet can now be used.

carb3.JPG

Regards,
MB

[Davw]

I have mine blocked completely - what is the advantage of running a small jet in the main air corrector?

[Robbie]

been looking at this Dave.It seems that you can iron out the flat spot in the lower rev range by running slightly open air correctors and a bigger main.would take a lot of messing on dyno.But I know that Ray had good results with the dynojet stage 7 kit wich is the brass bit for blocking the air corrector but with small hole.So this idea would let you fine tune it a bit better.Anybody had much experiance trying this?

[Fatspanner #44]

If your revs are down where the flat spot is then you are going too slow

[mick41zxr]

Robbie was chasing some of the brass correctors so I posted these pics show show another way around it.
Some of the brass correctors from kit manufacturers block the main air circuit, some are drilled to reduce the main air circuit.
The function of the main air jet is to feed the emulsion tubes.

cvp_velocity_tube.jpg

Emulsion tubes are fed by the main jet. Emulsion tubes, as the name suggests, mix air & fuel to assist atomisation as the air/fuel mixture is drawn through the needle jet into to the carb venturi.

Carb3.JPG

What the effect is fuel is drawn through the needle jet as a foam mixture as opposed to blobs of fuel.
Generally the larger the main air jet, the larger the main jet required to compensate for the fuel displaced the extra air.
If the air/fuel curve is too rich in the mid range (while carb is running on needle circuit) you can reduce the size of the main air jet, correspondingly you can run a smaller main jet, this will lean out the carb while maintaining correct jetting for top end. This can be useful if the mid range or needle circuit is too rich & a leaner needle is not available or cannot be lowered into the carb.
The main air jet is most effective from peak torque to redline, but like all thing carburettion every jet/clip/turn will effect other areas of the carb. so at all times you have to make compromises. But with a bit of work you can get jetting pretty good.
Will try to post some dyno graphs to show the effect.
Regards,
MB

[mick41zxr]

Ok here are some graphs of same ZXR with different combinations of Main & Main Air jets,
Run #3 has 120 Main Jet & 60 Main Air Jet
Run #4 has 140 Main Jet & 88 Main Air Jet
Run #10 has 150 Main Jet & 110 Main Air Jet

Dyno.jpg

Regards,
MB

[stuzx4r]

hi, i have the air jets linked to a solanoid, this allows the jets to be open at lower revs and closed at high revs (best of both worlds).
the solonoid is triggered from the CDI box.
End result 76 bhp with no dip in the mid range .

the kit was installed by dynopro in runcorn. 01928 576663

[zimm]

hi, i have the air jets linked to a solanoid, this allows the jets to be open at lower revs and closed at high revs (best of both worlds).
the solonoid is triggered from the CDI box.
End result 76 bhp with no dip in the mid range .

the kit was installed by dynopro in runcorn. 01928 576663

sneaky baskets .. i recall talking to chris about that as a possibility a year or so ago.. interesting that they've done it now.

[Robbie]

How much was this kit?
bet it was bloody expensive

[stuzx4r]

the kit was not that expensive, the biggest cost involved was changing from the standard cdi to a programmable one (with feeds off it to trigger the solenoid), as I was about to upgrading the cdi anyway it made sense to take the next step.

it did take chris a fair amount of dyno time to get the jetting and solenoid trigger timing spot on, but what a difference now its all done.

to get a true price you would need to phone them as mine was done "experimentaly"

[Robbie]

Do you have a dyno print out that you could post up??
cheers

[stuzx4r]

i do have a dyno sheet, how do i get it on to here though? not very good with compters!

thanks.

[stuzx4r]

Copy of dyno.JPG

i think this may have got it,