synchronizing weber 40 ida's

[krobb]

Wondering if someone can help? I just rebuilt my weber 40 ida's. Soaked it all in parts cleaner, carb cleaner and compressed air. All passages seemed to be cleared, reassembled it. I'm trying to install and balance them. The problem is that the syncronizer measuring the left carb bank is reading between 6-7 at 1000 rpm. The right carb bank is reading 3.5 - 4 (this is with the linkage detached and the idle screws turned in 1/2 turn on each bank). I can only get the right bank to register the same as the left bank if I turn the idle adjustment screw in about 4 turns!!!
My initial settings are:
idle air correction 1/8 turn out
idle mixture screws 2 turns out
anyone know the reason why this is happening?
any help appreciated,
thanks,
Keith

[JohnJL]

Check all your mixture screws are the same...I found a mismatched one on mine that needed very different settings to get it synced

[JohnJL]

Also, mixture shouldnt be the primary adjustment is setting your balance, you should be adjusting your air screws to get them synced.

Are you seeing those numbers across all the cylinders as an average (is 6-7 on the entire left bank and 3.5-4 on the entire right bank?)

[2.7RACER]

Hi Keith,
You mentioned the left carb is pulling more air than the right side with both idle stop screws turned in 1/2 turn.

I have found the butterflies, even fully backed off at the idle speed stop screw, are not often closed equally.

I suspect your left side butterflies are not fully closed when the idle speed stop screw is backed off.

I would remove the carbs, drain the fuel out, flip both carbs over and compare how the butterflies are closed.

Chances are good the left assembly isn't fully closed, even with the idle speed stop screw backed completely off.

This can be caused by the shaft coupler out of adjustment, or one or more butterfly discs not seating properly in the carb bore.

Some light will pass a closed butterfly disc. The is normal and is as designed.

The key is both sdes need to close equally.

It may be necessary to reset the shaft coupler or reset the butterfly disc.

Caution here............The screws holding the butterfly disc to the shaft are peened over so they will not back out.

If you need to reset a disc, use a screw driver that exactly fits the screw slot. Use caution loosening the screws. Once the disc is reset carefully retighten the screws.

Do not remove the screws holding the disc, loosen just enough to move the disc.

You do not want either screw to fall into the engine.

Further I would check the right side butterfly shaft for excess play.

If the right side carb is pulling air from a shaft leak or other air leak the synchrometer will not read that air.

I don't start with the idle stop screw turned in 1/2 turn unless it is the only way to keep the motor idling.

If the motor will idle with the idle stop screw fully backed off or just turned in slightly that is what I do.

An idle speed stop screw turned in too much will bypass air and fuel around the idle fuel and idle air screws making idle adjustment difficult.

There is more, but this should get you started.

[krobb]

Hi JohnJL, thanks for your suggestions. I will definitely check the mixture screws to see if they are the same. You are correct, all 3 carbs on the left side give readings between 6-7 each. All 3 carbs on the right side give readings between 3.5-4 each. I haven't bothered to sync each carb with the others on the same side. I am assuming that once I get the left to right sync done, the individual syncing shouldn't be too hard (I should know better than to say that!)

Hi 2.7RACER
thanks for your suggestions. I like the idea of swapping carbs which at least can narrow it down to a carb problem or something else. I see what you mean about keeping the idle adjustment screws backed off as much a possible so adjustments can be made to the air correction and the idle mixture screws. When I redbuilt the carbs, I did not notice any play in the throttle shafts. There were no grooves or wear marks at all in any of the throttle housings either. I placed a flashlight under each (closed) throttle valve (in each carb) in a totally darkened room and I was able to see a "ring" of light around the space between the throttle valve and the housing. I replaced all gaskets from the head/manifold up to the velocity stacks so I hope that an air leak is not likely here. I never considered an air leak in the throttle shaft but I am assuming that since the throttle shafts seem tight, there should not be a leak?
Do you know what the synchrometer readings should be (ballpark figure even) on an engine at idle?

Well, these sugesstions should keep me busy and I will post how it all turns out.
Thank you for your time guys.

1968 Porsche 911L 2.0L

[2.7RACER]

Hi krobb,
Another thing to look at is the condition of the O-rings at the idle jet holder and the idle fuel mixture screw.
If in doubt I would replace the O-rings. I was able to find suitable replacements at my local auto parts.
Before re-installing the carbs I would try to get the right and left butterflies as close as possible to each other. This could involve backing off the idle speed screw on the left side as compared to the right side.
Once you have the idle working right, I feel the most important adjustment is to synchronize the left and right carbs at 3000 rpm.
3000 rpm's and above is ultimately the rpm's where you run the car.
This is not to say synchronizing idle to 2500 isn't important, because it affects driveability and mileage.
I actually use 2 synchrometers. It is easier to monitor at all the various rpm's.
Of course make sure both synchrometers read the same.
Good luck and please keep us informed of your progress.