512BB Timing and Carb Setting

Ok, on to carb setting.

I ordered a STE SK Synchrometer and color tune today. I re-read the Haynes and Braden manual on setting webber carburetors along with JRV's Daytona writeup.

I believe the distributor to be in good condition since the timing and advance appear to be dead on. Will install new plugs. Here is what I believe is the proceedure:

1) Set air bleed of each carb to get equal reading on all 3 throats.

2) Adjust idle screw to get all four carbs to read same air flow. Pick middle flow rate carb and adjust others up and down using idle setting.

3) Use colortune and set idle mixtures.

4) Reset timing

5) Go back and do it again.

Did I get it right?

A couple of questions?

First where do I start with the air bleed screws. The Haynes manual recommends all the way in? Also as I turn "out" the screw it lets more air bypass the throttle plate so the air flow goes down? I' not sure of this one?

Second, once the throats of an individual carb are flowing the same amount of air I have to make sure all four carbs match. I do this by adjusting the idle screws of the carbs that are higher and lower. OK, fine. But what insures that as I adjust the idle screw that the throttle will be in correct allignment with the idle jet hole so that the progressing phase comes on smoothly? Is there a reference to start from that insures this or do I have my logic wrong?

At this point I am more interested in understanding "how this works" than a regimented proceedure.

Any help without giving away trade secrets appreciated.

Drew Altemara

Drew,

I'd leave the air bleeds alone until you've balanced the 2 primary ports and 2 secondary ports.

4 Webers is slightly different procedurally than 6 webers.

OK, you got me? What are the 2 primary ports and the two secondary ports? Now I'm really in the dark.

Drew

sorry.

Two of the carbs lead and the other two follow by way of the linkage arrangement. The two carbs that are hard linked are the primarary, the two carbs that operate off those by spring loaded linkage pieces with the setting screw are the secondary...if you are familiar with carbed 308's Boxer carbs are linked in the same basic manner.

Because of this arrangement the Two Cylinders on the Idle speed adjustment screw side of the Carbs are set first to each other, cross bank, then the two secondary carbs are balanced to them. So in the first phase, Air Readings are only taken off 4 cylinders not all 12, and only the 4 on the linkage endof each carb.

We together on this so far?

Got the first part, primary and secondary.

Had to read the second part a couple of times but I believe I understand.

You set up one cylinder of each carb cross bank, and those cylinders are the ones with the idle speed adjustment screws which I believe are the foward throat of the LR and the forward throat of the RR.

Then move to the secondary and set what would be the rear throat of the LF and the rear throat of the RF. Correct?

To do the above am I using the idle adjustment screws or the air bypass adjustment?

Just answered my own question on prior post. Idle adjustment screw.

Interresting discussions guys. This is my first post here so here goes.

I recently purchased a near complete set of new 40DCNF45/45/46/48 carbs for my 308. Well of course I had to tear them apart to confirm how they were setup. All the interchangeable stuff was as advertised. I still would like to find a new lever arm to convert one of the /45's to a /47 (left rear) carb. Anybody have a new one of these lever arms (has ball stud and a fork with an adjuster screw and spring fitted)?

Some observations:

1. The idle mixture screws were all 2-2.5 turns open. I set them all to 2.5 turns open.

2. One balance screw in each carb was closed. The other was open between 2-4 flats, then locked. This seems to imply that they may have been flowed on a bench during manufacture to ensure interbarrel balance.

3. The float levels were set to between 47-49 mm. Spec for this series of carb is 50 mm, so I reset them to that. Float droop for all was much less then spec for these carbs. The GT-4 WSM cites a stroke of 10.5 mm while my Haynes Weber manual specifies a stroke of 8.5 mm. I reset them to 8.5 mm as the sin here is to allow too much droop where they may hang up and not shut down the fuel flow when necessary.

Does anyone have a trick to negate the sloppy threads on the push rod end fittings? When I adjust these things the desired amount by twisting the rod ends, the adustment changes when I lock them with the lock nut. One thought is to try some teflon tape, swage the end fittings down a touch, or replace them.

Welcome aboard.

>>Anybody have a new one of these lever arms (has ball stud and a fork with an adjuster screw and spring fitted)? <<

I'll look around.

On the linkage...the lock nuts actually don't need to be very tight, after 20-30 years they will feel tighter than the gates of hell to the next guy {}.....

Is this your question?
All linkage is/should be adjusted after the carbs are set &amp; finished imo. Both nuts are loosened and the rod turned to get a nice but not real tight fit (yes it sometimes requires more than one try), then nuts tightened and the minute final adjustment made with the ball capture screws that locks with the cotter keys. It's important to check the rod lenghts at half &amp; full throttle (engine Not running) also to insure they are the same lenght and provide equal travel. Also, after adjustment but before final tighten one must gently pull throttle cable while very carefully obseving both lead carbs to insure both lead levers start moving at the exact same time. Once one has carefully viewed every different portion of operations you will see any tiny tweeks you need to make and how to go about them.

HTH's