tri power question?

Question

are tri powers or dual quads hard to tune. and how does one go about it?

Answer 1

I own a shop, and do a lot of drag racing. I have owned all kinds of tri-power set-ups before. Tune them with a vacuum gage and a tach. You will want to get the idle speed to around 800-850 rpm's. Turn the idle mixture screw on one side of the front carb (#1) until it reaches the best vacuum reading, reset the idle, and move to carb #2. Turn the same screw on #2 until you reach best vacuum reading, and reset idle speed. Repeat this process until you have all three on the same side adjusted. Now, got to the other side of the carbs, and do the same process. When you get the best reading out of all of them on both sides of the carbs, you are now ready to tune them. Start on one side of the first carb, and turn the idle mixture screw in (clockwise) until the idle speed begins to fall off, and turn it (counter clockwise) the other way until it begins to run smooth, and go another 1/4-1/2 a turn more. Now, repeat this process with the other idle mixture screw on the #1 carburetor. Move to the #2 carburetor, repeat the process, and then the #3 carburetor. If for some reason you can't get the idle speed down to do this, then suspect a vacuum leak somewhere. With a hiperformance cam that requires a fast idle speed, you may have to use an analizer in the exhaust, or a special spark plug that allows you to see the flame to set up the carbs. I have lowered the ignition timing enough to bring the idle speed down to where I could do this process, and then raised it again once I got the carbs working. You can get one of the spark plugs from either www.summitracing.com, or www.jegs.com for setting the carburetors. They work very good, and unless you have bungs in the headers for O-2 sensors, you will have no place to use an analizer, so the special spark plugs is the way to go. You will really need two of them (one for each side) in order to do the job without stopping and changing the plug to the other side while you adjust that side.
Glad to help out, Good Luck!!!

Answer 2

I never had to tune dual quads, but I have had many tri-powers.
Fords and a Triumph, of all things.
The tri-power center carb is the only one with a choke and the only one with an idle circuit. The outer throttle plates close almost completely at idle.
The outer carbs are staggered to begin to come open about half throttle on the center carb and all three carbs reach full throttle at the same time. The outer carbs flow slightly more than the center carb and the jets are slightly richer than the center carb. The spark plugs are the clue to whether the jets need changing. When all eight are the same color grey then you don't change anything. The factory tri-powers are dual plane with the left outer carbs venturi on the same plane as the right center carb venturi. Sometimes you have to jet the planes separately.

Answer 3

I'm with mister ss. Every Chevrolet I've ever had in the mid to early 70's had a single Holley with vacuum secondaries. They were quite fool proof.

I had a 4 speed 65 Chevelle 350hp. 327 that ran 13.89 with 3.73's @ 102 mph. It had a 580 cfm. Holley with a slightly weaker spring in the secondary vacuum canister, a re-curved distributor and small 7 inch slicks. Not too hot you may say but it was a bone stock street driver.

The second was a 69 Chevelle 375hp. 396 automatic with 373's It had a 780 Holley and was no quicker in time but ran 105 mph. It needed gears and better tires.

427 blocks were cheap those days so it was time for a deck job, .030 over TRW pistons, nice fine hone job, rod reconditioning, balanced, and a valve job on the original iron heads. I didn't have the cash for a set of closed chamber aluminum heads. I dumped the motor in the same 69 Chevelle and what a ride that turned out to be. With 4.11's and a set of M&H Racemasters it went 12.83 @ 114 mph. Again it was a streetable car but a dangerious weapon. Carburation -- 780 Holley with vacuum secondaries.

For street use mechanical Holley's are a waste of gas and on an automatic car. They will not work at all. Street cars need velosity and that's what vacuum secondaries give you.

Answer 4

Tri-powers never made sense to me- try divideing 6 into 8 and ending up with a whole number without decimal points. On the other hand,Ive found dual quads on v-8s a pleasure to test and tune. My favorite is the super cobra-jet 429 in the '70 mustang! 2nd favorite was a custom 455 tunnel ramed '70 GTO!

Answer 5

Sbc Tri Power

Answer 6

Dual quads work fine for a street application, providing the primary venturi's are not to large of diameter for the engine vacume at off idle to cause activation of the main fuel circuit(booster venturi's). For the street stick with an inline dual plane manifold to avoid both intake/exhaust reversion pulses. Avoid crossrams/tunnelrams for street usage. Both primary circuits on the dual quads have the same adjustment features/procedures as a single quad. For best performance stick with vacume operated secondaries. A real problem may present itself in two rich of an idle, IF the carbs in question were not intended for a dual quad application. If this happens the primary idle feed restriction needs to be "restricted" so as to lean out the air/fuel ratio at idle.
Tri power has the advantage of ONE CENTRALIZED two barrel for idle/low speed operation. Sence all tri power induction systrms come in dual plane manifold design, meaning one barrel for each series of four cylinders, the induction pulse(vacume) is relativly high giving snappy low end performance. Once again, for street stay with vacume secondaries if at all possable. The center two barrel has the same fuel/air idle adjustment needles as most any other carburetors do also. If you have a tripower set up with vacume operated secondary holley's for mopar six packs, the outboard two secondary carbs are NOT complete drones as with the 67 thru 69 corvette holley tri power set up. Mopar engineering called for their vacume operated outboard secondary two barrel carbs to have air/fuel adjustment needles fitted for idle quality. These air/fuel idle needles are located UNDER the fuel bowls & installed in front of the air valve base plate.
Last note; tri power suffers when in high rpm operation due to the fact that the air valves are spaced to far apart. Fuel fall out due to one carburetors incoming air/fuel charge meeting another carburetors air/fuel charge causes EXCESSIVE turbulence. This causes the fuel to drop out of the intake manifolds air stream & form on the floor of the manifolds runners. This problem becomes more serious at over 6000rpm as the lean air charge causes the pistons to "super heat" & melt down.
The cylinders most affected are cylinders numbers one & two.

Answer 7

thats what I hear, I have never had either or had to tune one up that did, they say if you have the right linkage there not too bad but I have never really seen a good running tri-power yet, give me one good 4bbl. and it will smoke a tri-power on the same engine.