My Zenith carb adjusting / synching process

[gdub0717]

Question regarding vacuum connections

For the sake of clarity I want to make sure I understand the following statement from this thread:

' I took Jerry's advice and have linked the vacuum ports of each carb to the corresponding port of the other via vacuum tubing - both ported and manifold connections - this smoothed things out considerably on its own.'

1.Does this mean that the intake (passenger side) of the carbs should be tee'd together the run to the distributor?
2.Should I do anything with the drivers side vacuum ports or just leave them capped?

Constructed a sync tool using the clear tubing/ATF method. Also used coolwhip tubs and a vacuum gauge I had on hand (Tee'd with shut offs) going to the top of each carb.

So I am in the final stages of the carb adjustment sync process. I just want to make sure I am getting the best possible performance and running setup.

Thanks for the help!!

 

[HB Chris]

You link the driver side ports. I used the small port at base of carb and used vacuum hose. You can also use the smog/egr port at base of manifolds which is larger. I can't tell if it made a difference though.

 

[61porsche]

1. No, not necessary.

2. Yes, connect. The theory or practice is to smooth out any intake pulses, improve carb vacuum signal for better mixture, and equalize the two banks of cylinders 1,2,3 to 4,5,6 as in practice they rarely see the same mixture strengths due to manifold design. ( Unequal length runners.)

DYI- carb sync tools- make sure they seal even if you have to tape them on. Mind the plastic cap or lack of one for the choke linkage- air can bypass there.

As you get closer to optimum tune, small adjustments make differences. ( If not, something's wrong.) It is not exactly explained well by the repair manual as it was written for trained mechanics with new parts.

I cannot overstate the importance of making sure the ignition, timing, etc. is optimized first. Use a dwell meter, timing light, tach etc. A cheap vacuum guage is your friend to show you how you can get the most vacuum and then try to make both sides the same.

Now with all the contraptions, listen. Listen to the exhaust, look for the smoothest running state. I happen to focus on sprak plug wires at the cap to get them to stay steady and not vibrate or shake. There should be no shake.

Now, I can agree with Chris- if you're engine is in an optimum state, balancing the manifolds might not get you a noticible smoother running engine. It will get you a better signal ( intake charge/ fuel/air/ vacuum) signal. For me it did something positive and it was cheap. I had the hose and didn't have to worry about caps deteriorating/ leaking. As a matter of fact, my manifolds had the egr tube crimped and silver soldered. One was leaking for god only knows how long. Found it with a stupid piece of vacuum hose and fixed it. Another trick is to go back over all the screws, nuts, etc. on the carbs/ manifolds. A small leak here, another there makes a huge difference in Zeniths operation. You'd be surprized how much vacuum you pick up and that means fuel economy too.

Now, lastly. I keep saying that with two or more carbs it's mathematically probable it's one over more. I use the air mixture hole that's next to the main air jets on top to close them with my finger or a pencil with an eraser. That changes the mixture to a richer idle. based on that- gets rough, speeds up, or stays about the same tells me what to go fix. Rich, lean, just right.

Just keep asking. It's a journey until you understand.

 

[deQuincey]

Just keep asking. It's a journey until you understand.

+1
AND JERRY IS THE B E S T TEACHER !!!:lol::lol::lol:

 

[Stevehose]

1. I did because I like overkill but it probably doesn't make a difference. I teed them together and ran a line to the distributor. I also removed idle retard and capped at the distributor.

2. Drivers side are linked, this made a difference for me, I used the egr pipe capped in the middle after checking for connection tightness on the manifolds and ensuring no leaks anywhere. Capped the manifold vacuum ports used for retard. Otherwise thes can be linked if you've capped the old egr fittings.

PS. Consider the Carbmate. No risk of sucking oil into one carb from the monometer. Use with air meters for precise synching.

PPS. Yes, Jerry is the man.

1.Does this mean that the intake (passenger side) of the carbs should be tee'd together the run to the distributor?
2.Should I do anything with the drivers side vacuum ports or just leave them capped?

Constructed a sync tool using the clear tubing/ATF method. Also used coolwhip tubs and a vacuum gauge I had on hand (Tee'd with shut offs) going to the top of each carb.

So I am in the final stages of the carb adjustment sync process. I just want to make sure I am getting the best possible performance and running setup.

Thanks for the help!!

 

[Luis A.]

I also took off the 4 linkage swivels and adjusted the 2 to stock length (50.8mm) and the others to equal length which made it zero out with the main accelerator linkage

Steve, I'm getting ready to adjust my carbs following this procedure and I have a question. What does "...and the others to equal length..." refer to? Which "other" linkages?

Any other changes since you wrote this? It's a phenomenal thread, thanks for your contribution.

 

[Stevehose]

Hmmm, if i recall correctly the 2 black plastic linkage rods have a spec in the blue book at 40mm center to center, the 50.8mm number below must be the outside diameter spec which I must have found somewhere. I recall seeing a pic of a micometer gauge on it but can't find it.

Correct me if I am wrong, aren't there 2 other metal rods, the knurled one being at the rear carb? It's been a while so I don't exactly remember. If so these would be equaled as a starting point.

Things I would do differently or that aren't as important in hindsight:

1. Lose the cheapo Craftsman vac gauges. I am not sure they are accurate enough to use as a comparison, and the flutter makes them pretty useless. Maybe some higher quality dampened gauges would work better.

2. Just tune with the digital tach, Synchronmeter and the Carbmate.

3. Don't cap the retard port on the distributor, leave it open because I think capping it can affect the ability for the advance side to work. Still not to be used-only the advance.

4. There will be a compromise between idle and 3k rpm sync. Hard to get both perfect, I tend to err on perfect at idle and ok to be off a little at 3k, result is smoother idle and transition and not much if any issue at higher rpm's. But see what works for you.

5. Jerry's tip of covering the idle jet hole on the cover to test for rich or lean idleing is a good one.

6. Take the play out of the accelerator pedal linkage, adjust at both the firewall and the rotating plate on the block so that there is no wasted movement before the carb linkage moves. This will give you a nice smooth response and feedback to the foot with no lag etc.

7. Get a good flexible screwdriver for the mixture screws - 3rd degree burn warning.


Keep us posted.

Steve, I'm getting ready to adjust my carbs following this procedure and I have a question. What does "...and the others to equal length..." refer to? Which "other" linkages?

Any other changes since you wrote this? It's a phenomenal thread, thanks for your contribution.