[Tom Vaught]

Originally Posted by Teej

(I’m definitely going to take Dick up on his offer to swap it out, I just haven’t been able to catch up with him. )

Really right now you are chasing your tail on the center carb being rich.

As was said by others, get a proper center carb on the engine first and make sure all of the circuits are performing properly with just that carb. End carbs blocked off.

Then add the end carbs, there should be no lean spot when the end carbs start to open as you have two accelerator pumps that should be adding fuel as soon as you move the end carb lever on the driver's side. (I am assuming mechanical linkage here.)

Tom V.

[Teej]

Just wanted to post to this thread to say thank you for all the help/ideas/suggestions that everybody had in helping me with the carb issue.

The good news is that I am back and running on all three and my air/fuel ratio issue is no more. It idles at about 14.4 and at cruise is really close to 14.0. WOT is still a little lean at 13.7 but I think I can drop that down just a bit with jets in the outer carbs.

The bad news is that to solve this very frustrating problem, I ended up going with a completely different carburetor and so I don't know WHY I was having those issues. I like solving problems, but I also like understanding they reason behind it. It seemed like we tried everything, but never found "the thing" that caused it.

I have to throw out a very big Thank You! to Mr. Boneske specifically. He came to my rescue and provided me with the carb that allowed everything to fall into line. He's been very patient with all my questions and went out of his way to help me. He is a super nice guy and I can confidently suggest giving him a call if you are dealing with tri-powers. Much gratitude goes out his way, along with all the helpful people of this forum. (And yes, the forum providers as well, for hosting this site.)

Thanks again.

[Tom Vaught]

Originally Posted by Teej

Just wanted to post to this thread to say thank you for all the help/ideas/suggestions that everybody had in helping me with the carb issue.

The good news is that I am back and running on all three and my air/fuel ratio issue is no more. It idles at about 14.4 and at cruise is really close to 14.0. WOT is still a little lean at 13.7 but I think I can drop that down just a bit with jets in the outer carbs.

The bad news is that to solve this very frustrating problem, I ended up going with a completely different carburetor and so I don't know WHY I was having those issues. I like solving problems, but I also like understanding they reason behind it. It seemed like we tried everything, but never found "the thing" that caused it.

I have to throw out a very big Thank You! to Mr. Boneske specifically. He came to my rescue and provided me with the carb that allowed everything to fall into line. He's been very patient with all my questions and went out of his way to help me. He is a super nice guy and I can confidently suggest giving him a call if you are dealing with tri-powers. Much gratitude goes out his way, along with all the helpful people of this forum. (And yes, the forum providers as well, for hosting this site.)

Thanks again.

X2 on being a great contribution to the Tri-power guys.

Tom V.

[War eagle]

[QUOTE=carbking;5454357]Tuning on the tripower with the small ends is basically the same as tuning on the tripower with large ends, except easier, as the small ends throttle plates are easier to get to seal.

Suggestion:




Now tune the engine. Eliminate so many extra unknowns. I still believe you are going to find the power valve in the center carb open all the time. Being able to run on 57 jets in the center and still rich tells me fuel is coming from the power valve. Why is it open??? Don't know. Perhaps wrong venturi cluster gasket not allowing vacuum to actuating valve? Perhaps incompatible cluster? Swapping parts is risky. Didn't find this spec in your thread, but idle mixture control screws should be out maybe 1 to 1 1/4 turns.

QUOTE]

I am having this problem and very rich idle. Plugs foul. End carbs off and sealed manifold. I keep going back to the power valve and since no one mentioned that at least 2 different lengths of power valve and power piston exist, maybe this is some of the trouble. I was set to order a new piston and valve but stopped to measure the one in my center carb. Glad I did.
Power piston 2.378 OAL .. Aftermarket 2.300
Power valve .632 OAL .. Aftermarket .700 (includes stem on both)

Mixing any of these could have some bad results. After all the years have passed and numerous rebuilds, one cannot simply assume that the parts you find on the carb are correct. Do you experts know what correct lengths are for the center carb(7024175), 1964 manual trans are? Please post length of power piston and valve.

Also on the 1964 center carb gasket, I think I should have 2 holes for the throttle plates and just the 4 attaching holes? Kits have 1 oval hole or 2 holes with a bunch of slots etc. Where can I get the correct gasket? Need a couple.

[Jack Gifford]

It's possible to determine at what vacuum the power valve opens/closes. Working with the carb top casting (with the power valve actuator and spring in place), I made a small plate with a piece of tubing pressed into it that would bolt over the vacuum passage to the actuator (I think the plate needed to also block off a nearby passage?). Connecting a Mity-Vac along with a vacuum gauge to the tubing, you can observe the level of vacuum that moves the actuator. Then you can change springs until you get it where you want it. [Or- you can make it externally adjustable as I did]

[Dick Boneske]

As stated above, there are two power valve actuators. The large 2GC carbs use an actuator 2.300" long. The small center carbs use a LONGER rod measuring 2.378" long.

To change the vacuum required to open the power valve, I use a gram scale. Most of the stock power valve actuating rods require about 220 grams of pressure to overcome the spring. If you remove 8 turns of the spring, this is reduced to about 160 grams, which accommodates "mildly lumpy" aftermarket camshafts. For cams more radical than the RAIV, I set the spring pressure to about 120 grams. It is fairly simple to wind the spring off the small end of the rod a few turns at a time and check pressure with a gram scale. When you get the desired force, cut the spring and bend the end so it hugs the shaft.

All the power valves (the part that screws into the float bowl) require about 75 grams to open the valve. The 160 or 120 grams referred to above will open the power valve at reduced vacuum or no vaccum (WOT).

As most of you know, camshafts more radical than stock also require modification of the idle circuit. This includes the brass venturi tubes, idle bypass restrictors, throttle base idle adj. screw holes. The following information is for OEM Pontiac Tripower center carbs only. Single two barrel and non-Pontiac Rochester two barrels vary widely from the numbers below. Most stock brass venturi tubes are .030" to .035". Enlarging them to .038 to .040" makes quite a difference in idle air flow. The idle bypass restrictors are usually .046" stock. Enlarging them to .048"-.052" makes quite a difference in idle mixture. The holes in the throttle base are typically .068"-.070". You may have to open these to .073" to allow enough range of adjustment with your non-stock cam. Remember, once you enlarge these passages, there's no going back to stock unless you have spare parts.

[War eagle]

I am going to make up the plate Jack mentioned if for nothing else to make sure the power piston actually moves. I have traced the passage for the pwr piston and found it open and gaskets correct.
Thanks for confirming length Dick. The longer power piston then, is paired with the shorter power valve in the center carb. The shorter pwr piston, with the longer power valve. I have actually found incorrect mixing of the two in a chevy carb.
A private email made me rethink the rich idle with the power valve open. The only time the pwr piston works is with the loss of vacuum and then opens the power valve to supply the cluster more fuel. This action must be initiated by increasing the air flow signal thru the venturi. So even if the power valve is open, just like the jets at the bottom of the bowl, AT IDLE no extra fuel will be flowing thru the idle circuit. There is a good explanation of this action in the 1964 Pontiac Tempest Shop Manual. So I guess I need to keep looking for the rich condition I seem to be having.

[Tom Vaught]

Originally Posted by War eagle

So even if the power valve is open, just like the jets at the bottom of the bowl, AT IDLE no extra fuel will be flowing thru the idle circuit. There is a good explanation of this action in the 1964 Pontiac Tempest Shop Manual. So I guess I need to keep looking for the rich condition I seem to be having.

Same deal applies to Holley carbs, People blame the power valve for idle issues and it is impossible for the idle to be affected by the PVCRs due to the idle circuit being on a different circuit vs the main circuit/ PV circuit and not being active at that idle mode.

Tom V.