Carb. modification k10

[cooperke]

Hi, did anyone performed this modification?

http://4lug.bydemons.com/index.php?view=items&cid=1&id=3&option=com_quickfaq&Itemid=6

(Y)
Thanks cooperke

 

[curtis]

Nope never seen that before...

 

[cooperke]

I did this morning and it works like it says!!!


cooperke

 

[Makrakin08]

what sort of gains? is it alot faster?

 

[cooperke]

It has better acceleration. don't now yet how many fuel it will eat. i'll post it later.

cooperke

 

[Makrakin08]

minted might try this when i get home

 

[boyracergt]

arent micra hitachis dcz or something like that it says ea81 or ea82? but if it works might have to try this

 

[cooperke]

Yes, they are (dcz 306....). But they work the same way.

cooperke

 

[imp124]

is this mod reccommended?

 

[boyracergt]

tried this out on my spare carb and on micra carbs its actually easier then in that article. it looks like it could be a good improvement as it opens up the secondary chamber at over 1/3 throttle so no diffrence at crusing but should give more air and fuel at full and half throttle. next is to try it on the car if it works il post up a how to but heres a rough guide its really easier just a bit fiddly when the carbs on the car.

picture of the throttle on unmoded carb

and after the mod

i decided after the screws holding the acutator wouldnt budge it would be easier if i left it on so basiclly all i did was remove the hose as in pics below
before:

after, you should be able to see the hose i took off

then i cable tied the two levers together on the window side of the carb and this was enough to hold it and it seemed to be secure enough so im going to do it this way on the car also means to put it back to standard all you do is cut cable tie and put hose back on

note: remeber to block the vaccum pipe on the carb or it wont run.

 

[imp124]

can i ask why there are two butterfly valves on the carb then, also what does the vac pipe you have taken off do.

is there a noticeable power increase over 1/3 throttle?

cheers

steve

 

[cooperke]

Carburetor - Multiple carburetor barrels
While low performance carburetors may have only one barrel, most carburetors have more than one venturi, or "barrel", most commonly a two barrel, with 4 barrels being common in higher performance larger displacement engines, to accommodate the higher air flow rate with larger engine displacement. Multi-barrel carburetors can have non-identical primary and secondary barrel{s} of different sizes and calibrated to deliver different air/fuel mixtures; they can be actuated by the linkage or by engine vacuum in "progressive" fashion, so that the secondary barrels do not begin to open until the primaries are almost completely open. This is a desirable characteristic which maximizes airflow through the primary barrel(s) at most engine speeds, thereby maximizing the pressure "signal" from the venturis, but reduces the restriction in airflow at high speeds by adding cross-sectional area for greater airflow. These advantages may not be important in high-performance applications where part throttle operation is irrelevant, and the primaries and secondaries may all open at once, for simplicity and reliability
Hope this is usefull.

cooperke

 

[imp124]

sorry i only have every really worked on bike carbs so this is fairly new to me, so does the second valve open anyway at some point at high RPM as the vaccum increases as i assume this would normally open it?

sorry to be a pain!

steve

 

[cooperke]

The carburator has 2 barrels, but only the primary barrel will open under acceleration. It is not until the gas peddle is fully depressed and a certain amount of vacuum is created in the intake manifold that the 2nd barrel will open up.

cooperke

with the mod. the second barrel will open when the 1ste is 1/3 open. so you will have better acceleration when you push the pedal ( more air and fuel enters the chamber).

cooperke

What does the Weber carb.?

 

[Veseli]

The carburator has 2 barrels, but only the primary barrel will open under acceleration. It is not until the gas peddle is fully depressed and a certain amount of vacuum is created in the intake manifold that the 2nd barrel will open up.

This is not quite true. During acceleration the primary throttle plate opens completely as the pedal is being pressed. This produces low pressure in the intake manifold and opens the secondary throttle plate.

I'll try to explain this. When the engine accelerates the air suction increases (because the pistons go down more and more rapidly), but the air flow through the intake elements is too slow to satisfy the engine demands. Actually the air flow can't change instantly and because of that there is a difference in speed of air flow in every part of the intake. So the speed of air flow through the filter case opening to the atmosphere is much lower than the speed of air flow in front of intake valves, consequently the pressure in the manifold is lower than the atmospheric pressure (the faster the air flow is, the lower is the pressure - law of physics). When the acceleration is over and the engine speed is constant or have reached the maximum, the air flow through the intake stabilizes and it isn't different throughout the intake anymore.

The conclusion is that the secondary throttle plate opens while accelerating and then closes when the desired speed is achieved, thus improving the acceleration, but also lowering the fuel consumption. It is true that when the pedal is depressed, the secondary throttle plate opens and this is why the engines with this type of carburetor need some time to slow down.

The actual gains and losses with this modification are:
1. When the pedal is pressed over 1/3 the secondary throttle opens instantly and there is no lag that would be produced by vacuum elements. This means the acceleration is better.
2. When the pedal is depressed both throttle plates close at once and engine slows down faster. This also slightly improves fuel economy.
3. Because the second throttle is not closing on high revs the top speed rises a little, but the fuel consumption rises quite a lot. You'll probably get around 20MPG, and that is why you shouldn't do it.

I apologize for my not so good English, but it is not my first language.

 

[superls]

your english is fine mate, and what you wrote makes alot of sence and is the reason i havent done the mod, plus i like the kick of the second flap opening in 1st and second gear, lol.

 

[daveeeeee]

What does the Weber carb.?

weber carbs run three different "circuits" if you like, to put it in very very simple terms if set up right the idle jet is used up to around 2800rpm, 3000rpm + is governed by the main jet. there is also the accelerator pump jet which delivers extra fuel on acceleration. that is an extremely simple explanation.

 

[superls]

the standard hitachi also has one of them pumps.