TZR250 3MA

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3MA Carbs

3MA (general)

3MA Carbs are a well discussed item on forums.
Lets see if we can resolve some mysteries.

Here you have the route that the air stream has to travel.
From solenoid unit to the emulsion tube.

And here is the airjet solenoids control map.
Measured by TPS and RPM

Here a image from the oem airjet solenoid unit
(you see two rows off jets, one row is for one carb)
Top shows us the connections for the tubes that goes to the carbs

How does they works:
Middle airjet is always open, the other two are controlled by the solenoids.
When activated, they open a airstream to the airjets.
(They are controlled by a mass signal coming from the CDI)

Example setup: (used for our calculations)
-airjet 1 is 100 (middle, always open)
-airjet 2 is 50 (left)
-airjet 3 is 150 (right)

Let just start with a example:
Point (1)

Engine is running 4000rpm (1/4 till 1/2 throttle)
On the chart you see that solenoid 2 and 3 are open.
What does this mean:
-airjet 100 (1) is open (always)
-airjet  50 (2) is open
-airjet 150 (3) is open

A total airjet off 300 is open. (leaning the carbs max)

You accelerate with the 3MA:
Point (2)

Engine is running 8000rpm (1/2 till full throttle)
On the Chart you see that solenoid 2 is closed and 3 is open.
What does this mean:
-airjet 100 (1) is open
-airjet 50 (2) is closed
-airjet 150 (3) is open

A total airjet off 250 is open (leaning the carbs midium)

You accelerate to max rpm:
Point (3)

Engine is running 12000rpm (1/2 till full throttle)
what does this mean:
-airjet 100 (1) is open
-airjet 50 (2) is open
-airjet 150 (3) is closed

A total airjet off 150 is open (leaning the carbs min)

Now we know how the jets are controlled and what they open. But how do they control the carbs?
That is all happening in the emulsion tube.


We go to our three examples (point 1, 2 and 3)
(fuel is (example) 1000 particles)

Point 1
A airstream off 300 goes trough the hose going from the airjet solenoids to the carb body.
There it is lead internal to the emulsion tube where or 300 air particles are mixed with fuel particles.
The more air particles we have, the leaner the carb will be.
1000/300= 3,33 (is in our example max lean)

Point 2
A airstrem of 250 will give us;
1000/250= 4 (in our example mid lean)

Point 3
A airstream of 150 will give us:
1000/150= 6,66 (in our example min lean)

Du to engine designe: (Fuel building problem)
The 3MA has trouble in the low and mid section
You can see that Yamaha is leaning the carbs enormous in the lower rpm range.
(lower Graphic on the dyno sheet, oem controlled airjets)
They probably have done that to overcome the fuel building problem when driving on low RPM's

When you have a stock 3MA and only use it for cruising down the road, best is to leaf it stock.
This is the best setup you can have, as yamaha really put some effort in setting it up right before selling it to the crowed.

To simplify the carbs, a common Mod is to remove the variable airjet system.
Serval options are here: link and link

When the variable airjet system is removed and a fixed airjet is placed, the carbs wont be leaned in the lower rpm range.
This results most off the time in a worse (rich) low to mid rpm range.
For a track bike not a big problem, as you already are in the higher rpm.
For a road bike this is less ideal.

The only variable you have to setup your carbs with a fixed airjet are

-Size off the fixed airjet
-Size off the needle jet
-Size off the Needle
-Size off the main jet

But for controlling the low till mid rpm, most is done by the
-Needle jet
-Needle

Now we are coming to the expensive part off the 3MA carbs.
Needle and Needle jet are the ones you can play with, but expensive to buy.


The 3MA has used different Needle jets and needles through the years wich can be used.
A well known Combination is the use off the Q4 (from the 30mm carbs off the 3MA3) needlejets in the (32mm carbs off the 3MA1

 

Needle jets:
-3MA1 has the Q8's or the Q9's
-3MA3 has the Q4's

-3MA3 uses the 30mm's
-3MA1 uses the 32mm's

Needles:
-3MA1 on the left (6L02-63-2)
-3MA3 on the right (6ZL-10)

Bowl Differences

Last but least.

I wont be placing exact carbs setup's as its impossible to do. (every 3MA has his own setup to work best)
Just giving indications (also these indications can not be used one on one you need to workout what's best for your bike)
(with indication range I mean +50 till - 50 example: 300 is in the range 250 till 300 300 to 350mains)

1) Placing performance exhausts on a complete stock bike (working variable airjet system and snorkels placed), your carbs needs rejetting.The stock 190 mains will not work.
(a indication is around the 250 range)

2) Using performance exhausts on a 3MA witch has the snorkels removed but with working variable airjet system, your carbs need rejetting
(a indication is around the 400 range)

3) Using performance exhausts on a 3MA with removed snorkels and a fixed airjet (120 till 130), your carbs need rejetting
(a indication is around the 300 range)

4) When using a fixed airjet (120 till 130) on a complete stock bike(exhaust rings in place, snorkels mounted), your carbs need rejetting
(a indication is around the 200)

5) When using a fixed airjet (120 till 130) on a derestricted 3MA (exhaust rings removed, snorkels removed), your carbs need rejetting
(a indication is around the 300 range)

 

And the last note/tip

You see that in the higher rpm airjet 2 is opening to.
Best is to open a small airjet, not a big one as you will be leaning the carbs big in the high rpm range.

How do you know which airjet is 2
Put the bike on contact (engine not running) and give full throttle, you hear one solenoid clicking.
That is solenoid 2 and it needs the small jet.

 
 
 
 
 
 
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