Thread: tri carb linkage movement

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I'm setting up the linkage on tri carbs, and I'm getting a little confused. It appears to me that the center carb, is connected in a one to one ratio with the first, and the first is in a one to one ratio with the third. Thus, the first and third carbs never open completely up. They only open, as far as the movement of the center carb, when making the connection with the first. I hope this makes sense. I thought the first and third carbs opened progressively, or faster or quicker than the center, once they were engaged. So, by the time the center carb opens its last half distance of linkage travel, the other two are completely opened - thus all three are wide open at full throttle. Help. Thanks

On my setup, the center carb linkage controls the front and back carbs. The center opens about halfway and then opens the remaining two. The further you get your foot into it, the more open all three become. Front and rear are in sync with each other, while the center one only taps into the front and rear at a given point. On my system that point is adjustable.

It can be adjusted to open all three in sync or to never open the front and back and just run off of the center alone. Runs a little rich that way but can be done.

Another thing I guess I need to mention is that my linkage was home built not purchased, as several modifications needed to be made, and the store bought linkage wasn't up to the job. I think I still have the a progressive linkage setup in shrink wrap, Offenhauser I believe.

i make my own. this set up is adjustable and uses stock linkage

Thanks for the help. I can see I have some playing around to do to get them in sync... thanks

A picture's worth a bunch of words, maybe even a thousand or so. It would appear to be about a three to one ratio between the linkage connection on the secondaries and the primary / center carb. Is that about right? At what speed or rpm do the secondaries open, it appears about at one half throttle.... thanks much

Looking at the picture you provided, I noticed the vacumm hook up on the back of the manifold, what type of thing is that? I guess its obviously a rubber grommet, but did the metal piece come with it? Is this the only vacumm you have? thanks

From the looks of it he put a hole there that goes into the lifter valley and the metal piece is a PVC valve (I suspect the hose swings around and connects to a 90 degree fitting in the base of the center carb). This was likely done so that holes did not have to be drilled into the vintage valve covers.

As far as linkage goes there are a couple of different options if you build your own. The first picture (an old picture of my FE Tri-power set up) works basically like the one shine shows. Personally like to have the lower linkage adjustable also. If the linkage is too long or short it can cause one or both of the end carbs to hang slightly open causing real idle tuning problems.

The second picture is what I’m running on my Hemi. It’s fashioned pretty much after the original 390/406 Ford Tri-Power setups.

i hate holes in the valve covers. i use moon covers most of the time. i've done the pcv this way on everything for years. never a problem. if i dont run the filler tube i use a moon breather in the front of the valve cover. contrary to belief the pcv does not pull a vac in the crankcase. it's only a smog device. without a large vent you will have a leaker.

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