Setting up a Tri-Power Progressive Linkage
I get asked this a bit so have decided to do a simple tech on the basics of setting up the tri power progressive linkage.
This will just deal with setting up the linkage, as there are other issues depending on the type of carbs you use and the type of motor its going on that would need to be dealt with individually. Such as jets size, power valves etc.
Firstly, this is on a Y block intake that I set up for a customer. The carbs are Holley 94 variants. But the basics will hold true for most setups. The pictures will tell most of the story.
The first thing is to separate the carb base’s so you can see the butterfly’s. Of course, make sure that you keep the tops and screws of the carbs separate so you don’t mix them up.
You want to start with the butterfly’s closed. Then you add the centre carb arm, making sure that it is in an upright position and that the butterfly’s are firmly closed. You will need to hold them closed as without the resistance of the rest of the carb they will open freely, and even a slight opening will affect getting the set up to work down the track.
Repeat this for all carb arms.
You then want to start to add on the linkage’s starting with the longest one that connects the two end carbs.
Then add the progressive linkage arm that allows you to set when the two end carbs come into action. While doing this you want to set a starting point for the opening on the centre carb as to when you will start to bring in the two end carbs. I usually start with about 1/3 to a ¬Ω opening and then fine tune later.
Once this is done, I pull it all off the intake and then put the carbs back together and then bolt it all back onto the intake.
Two things that usually need to be done for tri power setups is
1. Rejetting the carbs. As usually I am playing with 97/94 carbs for these, and most are going on OHV motors, so I jet up the 94/97 carbs. Most 97’s had 45 jets in them so I usually go up 2-3 so 47-48 in the centre carb and come down 2-3 on the end two carbs. 94’s had 48-51 stock jets, so I do that same for them, up on the center and down on the end two.
2. I also close off the air fuel circuit on the end two carbs by screwing in the air-fuel mixture screws.
These two things are for a starting point. Depending on the cubic inch of you motor you may need to alter and play. Also a unisyn is really needed to make sure you getting the right vacuum on the end two carbs.
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