Mindlos

[A20A1]

:D

On the Weber the Air correction jets are 0.20mm or 0.30mm larger then the corresponding main jets. I think the primary air correction is removable and the secondary isn't. If you look under the top hat you'll see 2 brass jets like the ones in the float bowl... but those are a part of the air jet controller and are not the actual air correction jet.

If you look between the silver metal tube and the spring loaded power valve rod you'll see the secondary air correction jet. My suggestion is to up the size of this jet to at least match the size of the secondary main jet. If the air jet controller is disabled then there should be no additional air correction being added.

I just re-realized that ABC might be all for the primary.

The primary air correction jet is close to the hinge for the float and is removable, that makes it easier to drill a spare one and swap between the two.

If you have a spare top hat it would be best... since you could cover the Air jet controller jets with metal putty and remove some of the potential vacuum leaks... that way when you drill the jets, the size you drill is the actual amount of air correction you get, so then you can use the + 0.20mm and see if you get a better response and less flooding and then hook up the accelerator pump again.


Make sure your power valve isn't stuck open. If you wanted to disable the power valve just to see the effects, I think a vacuum check valve would hold vacuum enough vacuum so the rod doesn’t drop back down when manifold vacuum drops… you could also remove the spring to relieve some tension.

[mindlos]

Alright. I'll get more bits to help measure my primary jet and for redrilling the primary air correction jet. I'm getting some spare carbs for a functional stock and donor. I'll continue on during the weekend when I have everything. The good thing is that the car is totally drivable with the air jet controller wide open. Somehow I dont miss the accelerator pump. Oh, its gonna take a week to get the A/F ratio meter unless I wanna go to a performance shop and pay out of my ass.

You are the man!!

[mindlos]

I replaced my O2 sensor and ran a wire into the cabin. Just to test things, the sensor read about 0.82V - 0.88V on idle and then went full scale 1.0+V with throttle. I will be testin, swappin, and continue rejettin the carb over the weekend since I got a spare and another one coming in. I will also take stock carb readings to find out. I love long weekends, even if it involves some painstakin procedures.

[A20A1]

You've been bitten by the carb bug... :lol

[mindlos]

Here is what stoichiometric is all about.

http://www.mindlos.com/~mandla/stoich.jpg

Here is how it relates to power and economy.

http://www.mindlos.com/~mandla/pwr-vs-econ.gif

Now here is the narrow band sensor voltage output (damn I wish I had wide band!!!)

http://www.mindlos.com/~mandla/sensor_voltage.gif


Pontification to come later (or not if discouraged).

[A20A1]

lol... Don't worry just post it anyways.

[mindlos]

I havent done any more carb modifications yet. The first mod was obviously too rich on the primary. It ran full scale 1V on the primary alone and was relatively leaner with the secondary involved at about 0.92-0.95V. The accelerator pump was not really needed at this jetting. Infact it was so rich on the primary that when I washed the car I found a film on soot on the bumper. Forgot to check my plugs though. This carb ran about 17mpg so no way I'm going down like that. To give a frame of reference, my driving habits land me at about 23mpg on a stock carb with no air jet controller.

On the last tank I basically ran a stock carb with all air jet controller ports plugged. The primary alone ran at about 0.77V and when the mechanical secondary got involved there was an momentary lean condition at about 0.15V then jumped back up to 0.82V. So it seems the secondary is jetted slighly richer than the primary. These dont matter much. Cruising without throttle is about 0.4-0.6V and when stopped and iddling I'm getting about 0.88V. Never goes lean because there is no engine management like EGR and other air correction that would lean out the mixture when no throttle is involved, which would make emissions and mileage much better.

If you consider the stoich sensor range inflection of 0.25-0.75V you can see that we are just a little rich but not by that much. And the reason for that is the air jet controller is not involved at all. But I still think it is not at the 12.6 max power ratio. That is going to be hard to get considering I dont have a wide band sensor without the steep inflection. My target would be to get a voltage of 0.88V and its just a gut feeling from looking at the graph and also considering the max rpm voltage I got when I was tuning the idle mixture screw.

[mindlos]

Well, I decided to make some assumptions and do some calculations to validate all this tinkering.
Assumption 1 the stock carb is jetted to run stoich ratio (14.7:1). Using 14.7:X = 12.6:1, I can calculate the percentage extra fuel needed to get 12.6:1. The value comes out to 14.7/12.6 = 1.17_ (17% more).

Now to get that much more fuel flow you would need to increase the hole's x-sectional area size by that much. Actually that is assumption 2. Since area has a square relationship to radius, the square root of 1.17 is 1.08. That means the radius/diameter must be 8 % bigger. That helps us determined the diameter of the bit needed to peform the redrilling.

So we can come up with this table:

1.00mm -> 1.08mm
1.05mm -> 1.13mm
1.10mm -> 1.19mm
1.15mm -> 1.24mm
...
1.60mm -> 1.72mm

I have 1.08mm and 1.18mm bits to try on the primary just in case the primary is not 1mm. I also got a 1.7mm bit for the secondary.