Air Jets

 

​Air jets.  What do they do?

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They meter air that's fed into the inner passages of the carbs.  Said air intermixes with similarly metered fuel from the float bowl.

How do they relate to the Pilot Circuit?

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daveo wrote:

How do they relate to the Pilot Circuit?

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They don't.
They are main air jets and nothing to do with the pilot circuit.
They adjust the air supply to the needle jet tube .
They perform the same function as my air correctors and fine tune the fuel mix on the transition from the pilot jet to the jet needle.
This is the area of the fuel slope that leans off and causes the off idle hesitiation / bogging when fitting pods or velocity stacks.
 

I will add there is an air jet on the pilot (slow) jet circuit that does have the same type of effect on that circuit. But is appears the jet you have posted about is as Zed indicated associated with the main jet/needle jet/jet needle circuit.

Air is pulled into the circuit associated with it and it allows air to be premixed with the fuel pulled up into that circuit. It sort of helps it (fuel/air mix) to become frothy and as it enters the carb throat it mixes with more air being pulled into the carb. Will add that the air jets not only have an effect on the volume of air but also on the velocity of it to some extent.

zed1015 wrote:

daveo wrote:

How do they relate to the Pilot Circuit?

🤓




 

They don't.
They are main air jets and nothing to do with the pilot circuit.
They adjust the air supply to the needle jet tube .
They perform the same function as my air correctors and fine tune the fuel mix on the transition from the pilot jet to the jet needle.
This is the area of the fuel slope that leans off and causes the off idle hesitiation / bogging when fitting pods or velocity stacks.

 

Is it common to install one or more different size air jets in a set of carbs to compensate for fuel mixture variations between cylinders?



 

daveo wrote:

zed1015 wrote:

daveo wrote:

How do they relate to the Pilot Circuit?

🤓







 

They don't.
They are main air jets and nothing to do with the pilot circuit.
They adjust the air supply to the needle jet tube .
They perform the same function as my air correctors and fine tune the fuel mix on the transition from the pilot jet to the jet needle.
This is the area of the fuel slope that leans off and causes the off idle hesitiation / bogging when fitting pods or velocity stacks.




 

Is it common to install one or more different size air jets in a set of carbs to compensate for fuel mixture variations between cylinders?






 

No!
The air jets perform a specific function and there should be no significant variations in A/F ratios between cylinders under normal circumstances to compensate for.
Apart from fine tuning the pilot mix on the fuel/air screws each carb should be jetted the same.
Any mixture strength differences on the same jetting will be as a result of faults such as intake air leaks or excessive component wear ( jet needles, choke plunger seals etc ) which should be addressed separately.
 

zed1015 wrote:

daveo wrote:

zed1015 wrote:

daveo wrote:

How do they relate to the Pilot Circuit?

🤓








 

They don't.
They are main air jets and nothing to do with the pilot circuit.
They adjust the air supply to the needle jet tube .
They perform the same function as my air correctors and fine tune the fuel mix on the transition from the pilot jet to the jet needle.
This is the area of the fuel slope that leans off and causes the off idle hesitiation / bogging when fitting pods or velocity stacks.





 

Is it common to install one or more different size air jets in a set of carbs to compensate for fuel mixture variations between cylinders?







 

No!
The air jets perform a specific function and there should be no significant variations in A/F ratios between cylinders under normal circumstances to compensate for.
Apart from fine tuning the pilot mix on the fuel/air screws each carb should be jetted the same.
Any mixture strength differences on the same jetting will be as a result of faults such as intake air leaks or excessive component wear which should be addressed separately.


 

It's been persistently rich on #1 and lean on #4 (but not excessively so), which was also the case on my old motor.
This carb set was purchased lightly used in 2015, and it's only had periodic low-tech carb-spray cleanings since then.

Hmmmm...


I do have to say she does run great...not quite perfect, but almost.   LOL!!!


I owe Rob another beer...

Are you reading plugs after high speed chops or just when coming to a normal stop.
No matter how hard you have ridden the readings from a normal stop will only show running conditions at idle which are usually rectified on the pilot screws.

 

The latter is my method since I live in the middle of a large city, and long stretches of road are 20 minutes away.  Besides that, I have no experience doing plug chops or how to go about it...yet.


It's firmly stuck in my mind that the pilot fuel screws on RS34 carbs have an adjustment range limited to 1/8 - 1/2 turns out from lightly seated.

That is what the Mikuni instruction manual specifies, so I keep the pilot fuel screws all set around 1/4 +/- turn out.

That I assume is correct if the orifice size itself was designed to limit how much fuel can pass through it, meaning any further than that the screws are backed out doesn't make any difference.

If I'm incorrect about that, then the Mikuni instructions are wrong...and how on earth could that possibly be.

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If the readings are just taken after a normal stop then you should only need to tune the mixture screws to correct your current readings for the pilot mix.
The Fuel type are very sensitive, a small adjustment can have a large effect and you can often go from normal running to fluffing plugs in traffic within a 1/4 turn.
There is also the likelyhood that even at the same setting like for like the screws are not all metering the same amount of fuel.
This can be due to previous over tightening and distortion of the seat or simply machining tolerance variations of the fuel screw tips.
I would start with the persistant rich number 1 and close it 1/8th a turn to lean it off and see how that looks after a few miles and adjust as necessary then once you are happy with that plug move to the lean one and follow the same procedure except start by opening the fuel screw a fraction to richen.
 

Yes sir!  Just a touch either way...

I just want to ride.  Lol!



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PSI compression-warm engine


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