Very basic multiple carb sync. tech

[tommy]

The victim... dual 97s as purchased. It ran OK but it needed attention.
I know I know The copper fuel line will be replaced!!!

This will be boring to many but if it helps a few that are just getting started, I'll be pleased. The steps will be the same if you are syncing 2, 4, 6 or 8 carbs. You'll just repeat the same steps a lot more.




The first thing to do is to loosen the link between the carbs so that each carb can be adjusted independently.



I use this Holley synchronizer. Others swear by the Uni-syn. It's all in what you get used to. This one is as simple as it gets. If you learn on a Uni-syn, that's what you'll be true to.



Rear carb reads just over 8. (red line between the numbers) The red line is actually the edge of a moveable vane or flapper. As the air volume increases the vane moves farther up the scale.



The front carb. Hmmmm. No measurable air flow at idle. It's idleing fine but only through the rear carb. There was no way of knowing that without the gauge.



Time to adjust the idle speed screws. I adjusted the front until the gauge started to show some air flow. Of course the engine is racing now. So I backed off the rear carb screw. A little more in the front. A little less in the rear. I'm not worried about idle speed at this time. I'm just trying to get the same gauge reading on both carbs. Once both carbs are flowing the same amount, you can lock down the link tying them together. The engine still may be idleing too high.



Now both carbs are reading just below 8...synchronized.

If it's still idleing too fast, back off one of the idle speed adjusting screws a few turns to disable it and adjust the idle speed of both carbs with the other carb's idle speed screw. With the link now hooked back up one carb speed screw will move both carb butterflys. You can also play with the idle mixture screws now. If the idle picks up with the mixture screw adjustment, back it down with the one working idle speed screw. When it's purring like a kitten and both carbs are still flowing the same cfm, bring the loose idle speed screw back up until it starts to make contact. You're done! The world is in harmony.

Before when I nailed it, the rear butterflys would hit their stops at WOT and not allow the front butterflys to open all the way so synchronizing can affect all out performance.

Pretty simple huh?

[BloodyKnuckles]

Thanks for taking the time to enlighten us. I did this exact process to my 3 1-barrels and made a tremendous difference. It is very simple and will make a world of difference.

Thanks again,


BloodyKnuckles

[BloodyKnuckles]

Damn, that's a big pic. Sorry


BloodyKnuckles

[oldcarmike]

Thanks. I've never had to synch up carbs (yet) but I've always wanted to know how. It's great seeing tech stuff "life sized" . I'd rather have a big picture than a grainy puny on.

[Automotive Stud]

Originally Posted by tommy

If it's still idleing too fast, back off one of the idle speed adjusting screws a few turns to disable it and adjust the idle speed of both carbs with the other carb's idle speed screw.

Could you clarify this a little for a moron like me?

When I did my 2 twos I left the idle speed screw out of one of the carbs, and loose on the other, so both carbs were totally closed, then set up the link, and adjusted the idle speed with one carb pulling open both. I don't think I could ever get a manifold like mine perfectly balanced, with the carbs so far back.

[tommy]

Originally Posted by Automotive Stud

Could you clarify this a little for a moron like me?

When I did my 2 twos I left the idle speed screw out of one of the carbs, and loose on the other, so both carbs were totally closed, then set up the link, and adjusted the idle speed with one carb pulling open both. I don't think I could ever get a manifold like mine perfectly balanced, with the carbs so far back.

That's the best you can do without out a gauge. It may be very close but if there is something that you can't see, the gauge will tell you how much air is actually passing through each carb. That's the same theory as running the mixture screws all the way in and then back them off 1 1/2 turns. That's a good place to start but you want to dial in each one.

As far as your intake, the carb doesn't know where it is mounted. It was engineered to add a specific amount of fuel based on the amount of air that passes through it. More air, more fuel. Less air, less fuel. The carb has no idea how many other carbs are doing the same thing on the same manifold. All it can do is add 'X" amount of fuel based on the speed of the air that is passing through it. The fuel to air ratio is set before the mixture passes over the butterflys and enters that or any other intake. That mixture doesn't change because it travels farther unless there is a vacuum leak that adds air to the intake that the carburetor can't sense. People have been running those manifolds successfully for 50 years. There may be better manifolds for racing applications, but it should be fine for the street. IMHO

[Automotive Stud]

Thanks Tommy, this is a great tech I didn't even know I needed! I dug through my tool box and found this beauty. Front carb pegged the gauge, rear carb was reading 8. I reinstalled the idle speed screw in the one carb, and I tweaked them so they were both reading just about 14 and the idle speed was the same. I just turned one screw in while turning the other out. Worked like a charm. Can I use this to adjust the mixture screws also?

[tommy]

Originally Posted by Automotive Stud

Thanks Tommy, this is a great tech I didn't even know I needed! I dug through my tool box and found this beauty. Front carb pegged the gauge, rear carb was reading 8. I reinstalled the idle speed screw in the one carb, and I tweaked them so they were both reading just about 14 and the idle speed was the same. I just turned one screw in while turning the other out. Worked like a charm. Can I use this to adjust the mixture screws also?

That's very cool!!! I've never seen one like it.

Does it just cover the carb throat like the one I showed or is there a hose to another plate that covers the carb throat?

I think most people adjust the mixture screws using a vacuum gauge. Play with the screws to get the highest vacuum reading with it plugged into the intake.

[Automotive Stud]

Originally Posted by tommy

That's very cool!!! I've never seen one like it.

Does it just cover the carb throat like the one I showed or is there a hose to another plate that covers the carb throat?

I think most people adjust the mixture screws using a vacuum gauge. Play with the screws to get the highest vacuum reading with it plugged into the intake.

Here's another shot. It sits into the top of the carb. There's also a rubber elbow in the box for doing side draft carbs. My dad had bought it and barely used it. I never knew how you were actually supposed to use it!

[Flathead Youngin']

cool, thanks tommy.....i'll be doing that soon...hopefully....

i bought the uni version.....i stuck it on my carb and it killed the motor..i adjusted it a few times to where it didn't kill the motor.....it has never read a thing on the little guage on the side.......either i'm doing something wrong or the import junk is playing with my head

[Petejoe]

Originally Posted by Flathead Youngin'

cool, thanks tommy.....i'll be doing that soon...hopefully....

i bought the uni version.....i stuck it on my carb and it killed the motor..i adjusted it a few times to where it didn't kill the motor.....it has never read a thing on the little guage on the side.......either i'm doing something wrong or the import junk is playing with my head

Youngin. The unisys can be adjusted by turning the round plate which opens the amount of air which can pass through without killing the motor.
I played with mine for a while threw it in the cabinent figuring it was junk than got it back out and started studying it. Duh...

[wrenchbender54]

Originally Posted by Flathead Youngin'

cool, thanks tommy.....i'll be doing that soon...hopefully....

i bought the uni version.....i stuck it on my carb and it killed the motor..i adjusted it a few times to where it didn't kill the motor.....it has never read a thing on the little guage on the side.......either i'm doing something wrong or the import junk is playing with my head

Same here. I put the Uni-syn on my 6 with the center cone backed out all of the way, then started turning it down until the bubble jumped. By then it was running like total shit, and then died. I threw it in the tool box and got out the vacuum gauge. I adjusted both carbs little by little until I had max. vacuum. Maybe I'll have to get it back out and piss with it some more.

WB54

[carbking]

Originally Posted by Flathead Youngin'

cool, thanks tommy.....i'll be doing that soon...hopefully....

i bought the uni version.....i stuck it on my carb and it killed the motor..i adjusted it a few times to where it didn't kill the motor.....it has never read a thing on the little guage on the side.......either i'm doing something wrong or the import junk is playing with my head

Call me at 573-392-7378 (9-4 Mon-Wed central time). Will be happy to explain it to you.

Jon.

[tommy]

I wish I could help but the Uni-syn kicked my ass 30 years ago. I fiddled with it for a week. I broke down and bought the one you see above and never looked back. I still have the Uni-syn in the bottom drawer of my tool box. Good luck.

[BobbedT]

Tommy, great Tech, I've never seen one of those before - where would I get one from?

Can you also post some pics of the whole car as it looks very KOOL from what I can see of it

cheers

Bob

[PEDDRO]

Originally Posted by BobbedT

Tommy, great Tech, I've never seen one of those before - where would I get one from?

Flatoz has the Unisyn units. PM him and he'll be able to help you.....(he's in Eastern Europe at the moment but will be back in the next couple of weeks).

[tommy]

Originally Posted by BobbedT

Tommy, great Tech, I've never seen one of those before - where would I get one from?

Can you also post some pics of the whole car as it looks very KOOL from what I can see of it

cheers

Bob

I couldn't find it on the Holley site, but it was still available a couple of years ago.

[arkracing]

Tommy -

is there a part number on the Holley Syncronizer?

[GTS225]

I get the feeling that your all suggesting that multiple vacuum guages are not an acceptable method of synchronizing multi-carb setups. I should really be going to a flow meter, not a vacuum meter. Am I correct?

Roger

[wrenchbender54]

Originally Posted by GTS225

I get the feeling that your all suggesting that multiple vacuum guages are not an acceptable method of synchronizing multi-carb setups. I should really be going to a flow meter, not a vacuum meter. Am I correct?

Roger

Not multiple vacuum gauges, just one. You can also use a tach. and adjust to max RPM. It's the same basic principal.