Tri-power questions - Pontiac GTO Forum
User Tag List

 2Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 12 (permalink) Old 06-17-2018, 03:58 PM Thread Starter
 
RunninLeMans's Avatar
 
Join Date: Apr 2014
Location: Maine
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Tri-power questions

I'm in the middle of getting my tri-power setup running and have a few questions. The motor is a '67 326, bored 0.060" over, Lunati Voodoo 213/219 cam, some sweet head work, about 9:1 compression, makes about 320 hp/375 ft-lbs according to the builder.

My end carbs look like they're weeping fuel from the accelerator pump squirts at just above idle. I do have a gage on the fuel supply and it runs about 6 psig, which I understand is about right. Also, I have the end carbs off right now because the butterflies were not seating completely and they were leaking vacuum. Would that bit of vacuum cause the carbs to weep?

I took the end carbs off and plated over the holes so I could get the center carb right. The car actually runs sweet on just the center carb, smoother and stronger at 1/2 and 3/4 throttle than the Edelbrock 500 cfm I had on there before. But I had to back out the idle screws almost four turns to get it to idle, and the idle still seems 'choppier' than it did with the Edelbrock. I rebuilt these three carbs myself and I blew out the idle circuits (and all the other circuits) when I had them apart. Plugs are new and looked bright and clean after a three-mile test run. Is this an unusual idle screw setting?

I had a little excitement on the first startup - the center carb float was stuck and fuel came squirting out the bowl vent all over the dizzy and wires. Everything must be sound, it didn't go up in flames!

Thanks for any feedback.
RunninLeMans is offline  
Sponsored Links
Advertisement
 
post #2 of 12 (permalink) Old 06-17-2018, 05:29 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,448
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Sounds like a fun running 326 and should be very peppy in a '64 body.

First, end carbs. Are you using the correct tri-power bases that do not have the idle mixture circuits or are you using standard carbs in place of the tri-power end carbs? Did you install throttle shaft bushings or new throttle shafts to make sure there is no play or air being pulled through the shafts?

Seating the throttle plates shut can become a problem during a rebuild. If they are just a hair off, the will not close completely and allow air/fuel to be drawn through. This is not just a problem that has just cropped up, but was a problem since they came out. Pontiac actually put a black coating of some type of sealer on the throttle blades to help seal them better. Many people when rebuilding them would clean this off thinking it was some kind of build up on the plates - and then have sealing problems.

I read an article that stated the best way to ensure that the throttle plates close perfectly tight with no air gaps, is to set them down on a light box and look down the bores checking for any light shining through. This would be best done BEFORE you completely tighten down the 2 small screws that hold the throttle blades to the shaft. Do one bald at a time and test it a bunch of times to make sure it seats and does not bind Once you are sure the blade is where it needs to be, then tighten the screws up. Then do the other throttle blade. Once you are satisfied that there is no light shining through and they close completely, stake the throttle plate screws so they do not back out. Although this is for a Holley carb, the principals for the throttle blades are the same: https://www.jegs.com/InstallationIns...-26-93-100.pdf

Next, there should be no leakage of gas from the end carbs just above idle IF the throttle plates are completely shut AND your float isn't set too high. The 6 pounds of fuel pressure may also be a problem as this was recently discussed. Factory Pontiac fuel pumps ran 2 pounds of pressure up to about 1800 RPM and then increases to around 6 pounds beyond that. It was recommended that a tri-power only needs 3 pounds of fuel pressure - but I feel this is too low with some cars having a bigger cam/jetted carbs and will suck the bowls dry on a good long full throttle blast. So you may need to add a fuel pressure regulator and set it at 5 pounds and see if that is enough. You could actually drop it until you feel the car "nose over" as it loses power on a full throttle run. Then just bump the pressure up another pound. There are also needle and seat assemblies that work better than others due to their design and will hold more pressure than some others that will not.

Your idle screw setting is fine. The general rule I have always gone by is to gently seat the idle mixture screws in and then back off 2 1/2 turns on each. Then back one side out until it runs smooth, run it in until it runs rough, then back out again until it runs smooth and leave it. Then repeat for the other side. I would not be too concerned about the choppy idle as it is most likely the cam specs over the carb settings and you will find a bigger cam needs more fuel to balance out the additional air it is taking in as compared to the factory cam. You cam looks mild, but with the smaller cubes, it is actually a big cam. Timing/idle RPM's can also play a role in choppy idle so you may want to play around with this to maximize the engine's performance.
PontiacJim is offline  
post #3 of 12 (permalink) Old 06-17-2018, 05:51 PM Thread Starter
 
RunninLeMans's Avatar
 
Join Date: Apr 2014
Location: Maine
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Thanks, Jim. They are true tri-power ends carbs, no choke, no thread on the blocked power valve hole and no drilling for idle screws. Timing is 36 after 2500 rpm, 18 initial and vacuum adds 18 back in so it's ~36 at idle with vacuum hooked up. Dizzy has had the treatment - been shimmed, bronze bushing installed and has one light/one medium spring.

I did the flashlight test after I pulled them, back carb is tight but front carb has some light around the blades, so I'm heading out to re-fit as best I can.

I usually install a big 4" vacuum gage that I own and adjust idle screws to highest vacuum, but there's no extra threaded ports in the stock manifold for this. I might have to modify one of my blocking plates so I can try that.
RunninLeMans is offline  
 
post #4 of 12 (permalink) Old 06-17-2018, 06:05 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,448
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Quote:
Originally Posted by RunninLeMans View Post
Thanks, Jim. They are true tri-power ends carbs, no choke, no thread on the blocked power valve hole and no drilling for idle screws. Timing is 36 after 2500 rpm, 18 initial and vacuum adds 18 back in so it's ~36 at idle with vacuum hooked up. Dizzy has had the treatment - been shimmed, bronze bushing installed and has one light/one medium spring.

I did the flashlight test after I pulled them, back carb is tight but front carb has some light around the blades, so I'm heading out to re-fit as best I can.

I usually install a big 4" vacuum gage that I own and adjust idle screws to highest vacuum, but there's no extra threaded ports in the stock manifold for this. I might have to modify one of my blocking plates so I can try that.
OK, sounds like you are on top of it. I would think you could run a vacuum line or a temporary "T" where the distributor vacuum advance line connects?
PontiacJim is offline  
post #5 of 12 (permalink) Old 06-17-2018, 06:58 PM
 
Join Date: Jan 2017
Posts: 161
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Just curious about this. Your putting a tripower on a 326 that's been bored .60 over, isn't that a bit too much fuel for that motor?? Don't the tripowers flow about 780 cfm?? Thanks.
Nicholas is online now  
post #6 of 12 (permalink) Old 06-17-2018, 07:54 PM Thread Starter
 
RunninLeMans's Avatar
 
Join Date: Apr 2014
Location: Maine
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Nicholas - yea, it's overkill, I'm doing it for the fun and the challenge of getting it running right, and because the tri-power setup is just so cool. I left the center carb jets alone, but swapped the 66 jets for 63 in the end carbs to lean them out a little, smaller than what would have been used on a 389 in 1964. I also have the linkage to play with, and may not end up with the ends carbs wide open at full throttle. We'll see if it bogs down or turns the plugs black.

Having said that, my actual 337 cubic inches with the cam and head work is not as far from the air consumption of the '64 389 as the simple displacement ratios of the two motors.

I just came in from tweaking, used the tach on my timing light to get the idle set, and adjusted one of the butterflies on the front carb. The accelerator pump rods were on the hairy edge of holding the butterflies open on both carbs, so I adjusted them so they pull closed. The light test still shows tiny specks here and there, but pretty adman close for metal-to-metal. Tomorrow will re-assemble and see what happens.

Jim - I notice one of the end carb bases has a plugged threaded hole below the butterflies that looks like it sees common manifold vacuum. I might try to use that somehow....
tiretread likes this.

Last edited by RunninLeMans; 06-17-2018 at 07:59 PM. Reason: update
RunninLeMans is offline  
post #7 of 12 (permalink) Old 06-17-2018, 08:44 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,448
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Quote:
Originally Posted by Nicholas View Post
Just curious about this. Your putting a tripower on a 326 that's been bored .60 over, isn't that a bit too much fuel for that motor?? Don't the tripowers flow about 780 cfm?? Thanks.

The 1956 316CI Pontiac engine offered a 285HP dual 4-Bbl carb (450CFM's each) - smaller than 326CI. In 1957, the tri-power was introduced on the 347CI engine - not too far off from the 337CI that 326 is now pushing.

The Pontiac tri-power had vacuum actuated outboard carbs for a slower and smoother opening as needed. Problem was that they could stick open as the vacuum canisters also closed the end carbs. Mechanical linkage was safer and had a spring return for positive closing.

Mopar uses vacuum to open its outboard carbs on the Six Pack set-up. The 340CI (again, not too far off from the 326/.060" 337 cubes) used the 3 Holley carbs rated at 930CFM's. The higher the engine revs, the more air it needs. So even though you might use one of those carb calculators, those are general rule and based on RPM's as well as other factors. Start building up the engine, and carb requirements change.
RunninLeMans likes this.
PontiacJim is offline  
post #8 of 12 (permalink) Old 06-18-2018, 07:55 AM
 
Join Date: Jan 2017
Posts: 161
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Yes, seeing a tripower on any Pontiac engine is impressive. Had one on my '67 GTO. If I recall correctly, in '56, Chevy offered a power pack 265 cu.in. engine, rated at 225 hp with dual 4 barrels. I think they each flowed about 450. Guess all that fuel worked fine back then.
Nicholas is online now  
post #9 of 12 (permalink) Old 06-18-2018, 06:09 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,448
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 347 Post(s)
Garage
Quote:
Originally Posted by Nicholas View Post
Yes, seeing a tripower on any Pontiac engine is impressive. Had one on my '67 GTO. If I recall correctly, in '56, Chevy offered a power pack 265 cu.in. engine, rated at 225 hp with dual 4 barrels. I think they each flowed about 450. Guess all that fuel worked fine back then.
Yep, many of the mid fifties cars had multiple carbs, The Chrysler Hemi with 2 x 4, the Caddy had the 2 x 4 and then a tri-power, Olds had the J-2 tri-power, Packard had a 2 x 4 on the Caribbean, etc.. These were not muscle cars by any means. These were luxury cars with the horsepower to move them - just as many of the earlier luxury cars did.

Some will say the 1955 Chrysler C-300 ushered in the muscle car era, but not true. The 1949 Olds 303CI OHV Rocket V8 engine was installed in its lighter straight 6-cylinder B-platform body called the Oldsmobile 88 bringing to light the big body V8 in a mid-sized body - ie the '64 GTO. In 1950, the "88" series adopted the name Rocket 88 which added the rocket to its logo. Beginning in 1949, it won many of the Nascar events from 1949-1953 - but so did Hudson's Twin H-Power 308CI inline 6-cylinder.

My Dad recalled that his father bought a 1950 Olds Rocket 88 and that it was one of the fastest cars on the road at the time recalling that many cars still had flat head & inline 6 & 8-cyl engines. They lived in the New York/New Jersey area and my Dad said his father would always come out of a toll booth wide open racing other cars of the day. So for its time, it was a fast car. LOL
PontiacJim is offline  
post #10 of 12 (permalink) Old 06-21-2018, 02:08 PM
64-67 Expert
 
geeteeohguy's Avatar
 
Join Date: Feb 2008
Location: Fresno, California
Posts: 8,457
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 98 Post(s)
I'll add, I experienced a tripower on a 326 powered 4 speed '65 GTO in the late '70's, and the car ran HARD. Also drove a '65 GTO with a 350 Pontiac out of a Ventura (smog motor) around the same time, with a TH350 and a tripower...the car was a rocket. You will be FINE with a tripower on that little 326!!
geeteeohguy is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Running a built 421, 65 GTO, Tri-power, considering a 66 Tri-power setup avman 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance 4 07-28-2018 10:46 AM
Tri power / timing questions My65goat 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance 35 08-28-2017 07:23 AM
Power Brakes with Tri Power timmyg 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 3 08-21-2013 03:10 PM
tri-power questions busaben 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 12 07-10-2009 01:30 PM
Power Windows, Power Locks, Seat Belts, Power Rear View Mirror, Back Speaker Location GQUINCOCES 1964-1974 Tempest, Lemans & GTO Convertible Top, Interior, Glass and Trunk 2 01-03-2009 07:18 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome