Air correction

Rickard M · 12-28-2007, 12:15 PM

Today I made a basic set up on my "new" Weber IDT with a garage vac,

This worked very well, but I noticed a problem that leads me to my question...
One barell flowed more than the two other on one carb. One "damper" (is that the right word for it?) didn't close 100% (it looked good, but when I put out the light in the room and held a flashlight by the venturi I could see that it wasn't as tight as the others) And of course it was one of the dampers that share the same axle piece with one more. I could almost get it perfect using the idle air correction screws. fully in on this and fully out on the other two. Is that OK to do it like that?? Is it bad to run with some screws so much out?

Thank's in advance
//Rickard

nabilious · 12-31-2007, 07:26 PM

You don't wanna use those screws for that big of an adustment. Just my opinion, I would try to adjust the butterfly if possible.
Nabil

Mo_Gearhead · 01-01-2008, 05:22 AM

OK, so I can understand this ...you have made a home-made 'flow bench' from a vacuum cleaner that allows you to pull air through the carbs.

You put your air flow meter on the individual 'stacks' and begin adjusting the mixture screws to balance the air flow???

To what purpose??

Are you tuning the vacuum cleaner???

Please educate this ignorant individual (me) on how 'tuning' the Webers to a artificial air flow is going to assist them when installed on a running, air-pulsing, gas flowing, etc. REAL engine????

304065 · 01-01-2008, 06:22 AM

Mo,

There's nothing wrong with getting the throttle plates set in the ballpark with a flow bench and then using the fine adjustment once it's on the car. The range of adjustment of the air corrector screws isn't so great that it could compensate if one of the butterflies was set at an angle different to the other two.

The factory manual sorta shows this, it shows the coupler between the long throttle shaft and the short one. If one barrel is flowing more than the other two, and the ONE is the one with the short shaft (I hope that translates into Swedish OK) then that's where you start, and the flow bench will probably work ok.

Mo_Gearhead · 01-01-2008, 07:04 AM

Yes, I understand the butterfly 'alignment' setting, ...but fiddling with the air/idle/mixture adjustment screws on a flow bench?

Useless IMO.

304065 · 01-01-2008, 08:23 AM

Yes, I concur that fiddling with the mixture screws on a flow bench is a useless exercise, insofar as there's no fuel.

I do this from time to time with my MFI throttle bodies to get them to all flow less than 3Kg/hr of air BEFORE going to the three hour process of mounting them on the engine. If you can't get them all the same on the bench, you certainly don't have a chance on the car, and fiddling with the air correction screws can tell you whether they are functioning properly, or whether the holes have carboned up or some buffoon (such as one with an early tachometer as his avatar) has bent the screws by tightening them too much.

Touching the idle stop screw other than to baseline the flow of one side against the other before it goes on the car likewise is an adjustment that would be repeated many, many times on the car and so not something I would bother with.

On with the show.

Rickard M · 07:12 AM

Thanks for the replies! Yes of course, I just wanted to see that as mush as possible was alright before I bolted them on the car. I wanted all barrels to be the same to start with and this was an easy way of doing it

I just adjusted the "AC" screws (on the nice picture that Jon posted above) The "bad" one that I discovered (I couldn't notice it just by looing at it) were on the long throttle shaft so I could not adjust it any better without make the other one worse. I couldn't get them all the same (almost, I think I were a half unit off on my Synchrometer) without having that screw in and the other two out.