[cjaghblb]

I recently got my hands on a repro base plate setup for the end carbs and I notice that the tiny airbleed hole in each throttle plate is not there. My original setups have this small hole (which I assume is for air bypass to balance out the idle). My question is simply do these holes make a significant idle quality difference or is it really unimportant if they are there? Thanks in advance!!

[tripwr1964]

the end carbs do not have an idle system, therefore shouldn't have the holes in the plates.

[67 Lamnas]

Originally Posted by cjaghblb

I recently got my hands on a repro base plate setup for the end carbs and I notice that the tiny airbleed hole in each throttle plate is not there. My original setups have this small hole (which I assume is for air bypass to balance out the idle). My question is simply do these holes make a significant idle quality difference or is it really unimportant if they are there? Thanks in advance!!

You can always add the holes later if desired/needed. The more important question is: "how well do the stamped throttle blades fit the bores??"

From what I've seen, the repop end carb bases have throttle blades that are stamped instead of machined (except for the excellent quality ones from Vintage Speed), and that the low-quality repop ones do not seal to the bores. Which obviously will make it impossible to tune/to get a decent idle.

Doesn't sound like you've installed yours yet, will be interesting to have you give us some feedback here.....I'm assuming you have the low quality ones from The Parts Place?

See link below with input from Mike Wasson of Mike's Tripowers......

http://forums.maxperformanceinc.com/...d.php?t=543619

[cjaghblb]

Originally Posted by tripwr1964

the end carbs do not have an idle system, therefore shouldn't have the holes in the plates.

I have 2 sets of original end carbs and both have the pin holes in the outer carb throttle plates and I have seen others with them so they are original and they serve a purpose that in my mind is one of 2 things:
-additional air for air by-pass (even though the idle circuit is only on the center carb) and yes it seems odd but maybe Pontiac Engineering decided it was beneficial on a multi carb setup.

-just an air bleed to help prevent the pressure difference between above and below the throttle blades from drawing them open slightly at part throttle when only running off the center carb.

I plan on adding them but I just wanted to get some opinions off this site from people more in the know than I.

BTW, mine is the stamped setup from TPP and so far the only complaint I have is about the assembly attention to detail. I have an intermediate level of experience with the TP setup and have rebuilt successfully in the past and so far this is OK in my book. I haven't put it on the car yet of course so thats the real test but you can visually see if it will be an issue before its even on the car and they are looking good from that perspective.

[old66tiger]

I bought a set of the bases from Vintage speed. They are a work of art. The blades seal perfectly and with a coat of paint on them, it is hard to tell the difference between the originals and the new ones. Mike Wasson doesn't have much of an opinion of the other repop bases. In comparison, the Vintage speed bases are the only repop bases to buy

I built a new 455 and tuned the center carb with block off plates in place of the end carbs. This was key as I made several mods and taking the center apart with the ends on would have been a pain. When I finally bolted the factory ends on, the idle quailty was so poor, I had to make a huge change to idle mixture setting and curb idle speed screw to get it to run half way right. The original ends didn't seal worth a damn so that is why I ended up buying a set from Vintage speed. BTW...took 2 months to get them.

As I mentioned earlier, the bases from Vintage speed are perfect, but they do not have the air bleed holes in the butterflies. When I finally installed the end bases, I noticed that when I cracked open the ends, the butterflies would hold open slightly, causing the engine to run fast like it had a vacuum leak. I did it several times and the same thing occured. They would eventually close, but it took several seconds. With the engine off, the butterflies snap close without any effort.

I sent my originals to Mike Wasson and he coated them with some sealer that is made specifically for poorly fitting throttle blades. I got them back and with a light throttle return spring, no more problems. I ended up sending my vintage speed bases to Mike for another customer.

I am thinking now that the Vintage speed bases fit too well and there isn't enough leakage to allow the bases to break vacuum when coming closed. It is entirely possible that the tiny hole in the throttle blades is necessary for that reason. Please let me know if you find that this is the case.

[67 Lamnas]

Originally Posted by old66tiger

I bought a set of the bases from Vintage speed. They are a work of art. The blades seal perfectly and with a coat of paint on them, it is hard to tell the difference between the originals and the new ones. Mike Wasson doesn't have much of an opinion of the other repop bases. In comparison, the Vintage speed bases are the only repop bases to buy

I built a new 455 and tuned the center carb with block off plates in place of the end carbs. This was key as I made several mods and taking the center apart with the ends on would have been a pain. When I finally bolted the factory ends on, the idle quailty was so poor, I had to make a huge change to idle mixture setting and curb idle speed screw to get it to run half way right. The original ends didn't seal worth a damn so that is why I ended up buying a set from Vintage speed. BTW...took 2 months to get them.

As I mentioned earlier, the bases from Vintage speed are perfect, but they do not have the air bleed holes in the butterflies. When I finally installed the end bases, I noticed that when I cracked open the ends, the butterflies would hold open slightly, causing the engine to run fast like it had a vacuum leak. I did it several times and the same thing occured. They would eventually close, but it took several seconds. With the engine off, the butterflies snap close without any effort.

I sent my originals to Mike Wasson and he coated them with some sealer that is made specifically for poorly fitting throttle blades. I got them back and with a light throttle return spring, no more problems. I ended up sending my vintage speed bases to Mike for another customer.

I am thinking now that the Vintage speed bases fit too well and there isn't enough leakage to allow the bases to break vacuum when coming closed. It is entirely possible that the tiny hole in the throttle blades is necessary for that reason. Please let me know if you find that this is the case.

Good post........The problem with the Vintage Speed bases is that he doesn't get the shaft length exactly right....they're a bit too long like about an 1/8" or so. The return spring gets caught in the space where the shaft protrudes past the casting and will cause the problem you describe. The shaft can be shortened.

[old66tiger]

67 Lamnas, I agree with you that the spring end of the shaft sticks out a bit too far. VS uses a very stout spring which I am sure is cheap insurance to make sure that the blades close entirely. I was able to bend the end of the spring a little to keep it from dropping between the lever and the base. Either way, the bases closed fine for me and I seriously don't think that was the root cause of the sluggish closing problem that I encountered. I didn't see any problem with the blades closing with the spring riding off of the base when the motor was not running. Here is an interesting tidbit...I cracked open the ends and they hung a bit. I shut off the motor and saw the blades close immediately after the motor shut off. Weird, huh?

[cjaghblb]

Interesting discussion. I noticed the shaft sticking out farther on the new base as well and further investigation shows its not because the shaft is longer but because the new base is dimensionally smaller. I don't care for the way the spring sits either but I can't see any reason for it to cause binding. I won't be using this new base on my new 66 TP build however as the superior fit and unrestricted motion of the shaft in the original base is obvious to me. I wouldn't hesitate to use the repro at this point but since I have better options currently, it goes into my parts bin.

Two questions:

Anyone do the DAG213 sealling process at home before? Is it reasonable for someone with ok skills in the garage to tackle? Where did you get the DAG213?

Is there a high temp lubricant for the throttle shaft out there that will last for some time??

Thanks all for the input

[cjaghblb]

old66tiger

Would you mind discussing the changes you made to your center carb? I did the same (used block off plates) on my 65 setup I currently have working on my existing motor.

I will be going to a 487 this time around and will need to work the tri-power to work here, I am looking at using a later center carb that has the 1 3/8 bore instead of the standard 1 3/16 bore and have a carb to use (I would like to find one in better shape though)

I understand that the 66 TP flows in the neighborhood of 750 CFM and the calculations we did on my motor would require a flow in the neighborhood of 850 so I really need to see what my options are.

I did consider the new Barry Grant setup but I haven't gotten the warm and fuzzies about its quality from the people I know that use them so far so I decided to stick with the evil I know quite well...the old tripower. I have tons of carbs and experience with them so here I go

I also thought I should stop being an idiot and just move to the better performing and easier to match to my application 4 barrel but i am mentally brainwashed by the TP and just have to have it.

So for your carb, what did you do besides adjusting the jet size and maybe install a softer power valve spring? Did you enlarge the idle tubes any? Float height? (24-25/36" hieght and 1/16" off the bottom for drop is what I use) Any changes to your air bypass holes in the throttle plates?

Any help is greatly appreciated because I will dyno this before it goes in the car and would like to have a solid idea about what I should do to my TP setup so I am not wasting time while there. Thanks in advance.

[tripwr1964]

would not having holes in you end carb plates cause a lean condition and high low idle? we spend so much time trying to seal these end carb, i would think that having holes in the plates would be no different than a poor fitting plate or a leaking gasket???? I have 3 sets of '64-'65 2G's and have no holes in the end plates. I would like to understand this if someone has an answer. thks Tim

[Tripower455]

My original '66 ends have tiny holes in them. My understanding is that they give a small vacuum signal to keep the primaries "primed" if you will.

[old66tiger]

As I think about the changes to my center, I have to chuckle at the headaches this has caused me over the past several months. I can honestly say that I am closer, but not where I want to be.

Here are the specs:

428 block 0.030"+, with 455 crank.
Eagle H-beam rods and Sealed Power pistons with lightweight pins
6X heads ported with 1.77" exhaust valves
XE274H cam with comp hydraulic lifters degreed on 110 LSA
RA HO Manifolds into 2.5" Pypes exhaust and X-over.
Stock Points ignition - I was running Pertronix for awhile but took it off because I thought that the ignition was causing rough idle. It wasn't.
The ignition is set up for 13 degrees initial, 35 degrees total and 14 degrees of vac advance. Advance is connected to manifold vacuum.
m-21 4-speed
3:55 gears
22570R14 tires
Stock center carb is modified:
idle tubes enlarged to 0.038"
0.065" main jets
0.100" holes in the throttle blades located near the shaft, but on the idle screw side of the blade.

I started with trying to get the center to run completely off of the idle circuit with little or no transfer slot showing below the blades. I started by enlarging the idle tubes to 0.035" with a 0.090” hole in the butterflies. I also started with 0.066 jets. I could not get the motor to idle fast enough so I tried opening up the idle tubes to 0.038". That had little effect on the idle. I opened up the holes in the butterflies to 0.1000” and that did very little. I had a spare throttle base and tried opening up the curb idle ports to 0.090” as suggested in Roe’s book and that made things worse. So, I went back to the stock base with an idle port opening of 0.070” and set the mixture screws in until the engine hesitated a bit then backed them out until I achieved peak vacuum. I was able to achieve decent idle with a bit more curb idle speed adjustment and about 1 turn out on the idle mixture screws. Saw in my motors book that the cars with the RA4 profile cams were specked to idle at 900-1000 rpms. WOW! I would have never thought that they would be that high. I am idling at about 850-900 rpms for this cam with 10-12” of vacuum. I never touched the power piston spring since I never saw any fuel dripping off of the venture cluster. I came to the conclusion that there is no way to get the engine to idle smoothly with this cam without a minimum of 0.025” of transfer slot showing below the blades.

The motor pulls 24" of vacuum when coasting down the road. The problem that I am having is that when I am running at a steady speed of 1000-2000 rpms, the car has a hesitation. This hesitation also exists when decelerating from 2300 rpms or so back to 1000 rpms. This is regardless of what gear I am in. I noticed that the vacuum also hesitates a little when the car hesitates - which I would expect with a 4-speed car. This is the last piece of the puzzle and hope that I can get this part ironed out. I tried every set of jets that I had available and I still can not get this hesitation to go away. I am going with a Accel street billet to see if ignition is part of the problem.

The only mods to the ends is 75 jets.
I have given up my purist ways and have embarked on building a dual quad setup with a pair of Pontiac AFB’s from the carb shop. I picked up a used OFFY intake off of EBAY and should have the setup completed in a few months. It will be period correct, just not a tri-power. I will still keep the tri-power for future use and because it is original to my car.

[sixt8bird]

I have heard that the small holes were there to suck in the fumes after you snap open the front and rear carbs. Think about the gas that would sit ontop of the plates without this small hole. You would pull into your garage and smell fumes. so the vacuum would just be enough through these holes to suck the fumes in and burn them. This is about the most logical reason so far that I have heard.

[Dick Boneske]

The holes in the throttle plates I've seen are less than .030". I've seen these only on unmolested '66 setups, so Pontiac Engineering (or Rochester) must have added them to correct some problem with the earlier Tripowers. I don't think any of you hit on the reason they did this.

I'm sure some of you have seen much larger holes in the throttle plates on single Rochester 2 barrel carbs. Some of these are .090 or larger. The reason for this is a little more obvious. These larger holes result in a leaner mixture with all other internal carb calibration remaining the same. For some reason, this method was chosen over modifying the idle tubes in the venturi cluster.

[Bronze66]

My tri-power set came off a 66 421 auto. It was unmolested when I got it. The end carbs do not have any holes in the throttle plates. they also did not seal very well either. Old66 I did the same as you with the idle ports. (Roes book) I used a different carb for the center. It is a 70 455 carb. A bit larger than the stock one. I enlarged the idle port to around .093. Prior to enlarging the idle tubes. It helped the idle and then enlarging the tubes also helped and stopped any leanness when cruising and just off idle using the transfer slot. I did refit the end plates which made things better, but had to compensate with center carb to make a little richer because they did not seal all the way around still. I did use a ceramic coating on the end plates beginning of last year. It helped some. Can DIAG213 be bought someplace? Old66 you may have to balance the idle ports and tubes together to get a better idle. Your tubes seem to big at .038. You can pull them out to change or solder closed and redrill. I have a 228 solid cam on a 108lca and I can get my motor to idle at 600rpms. I only have a 389 +.030. Your larger engine may be more of a challenge.

I am wondering if the engine size and or trans type may have required the holes in the end plates or different years. I thought they were all the same. Guess not uh.

[sixt8bird]

The holes on my 1966 end carbs are as small as a needle tip, you hardly can even notice them. .030 is way bigger than what is on mine. I'll see if I can take a picture in the next few days. I spent months searching for Dag 213 and found a company out of Canada that sold large amounts to Aircraft builders but had no interest to sell it to an automotive enthusiast. I know you could buy small packets of the stuff as i saw some at a carb shop a few years ago. He said a customer brought it in.

[cjaghblb]

I measured the hole size and it comes in at .030 and here is a picture of them for you all. I have three sets of end carbs and they all have them save the one with the TPP repro base. I will be adding the holes.

[sixt8bird]

Those dont look like .030 The gap of a spark plug is .035 which is only .005 bigger and the gap of a plug visually looks way bigger than the holes you have? Are you sure its not a number 30 drill bit? The aftermarket from Vintage speed are good but there are some questions, why would they install the screws under the plates instead of above? .
They dont have any holes but my Tri power after many mods to the center carb now starts better than it ever did and runs real strong but has a very very small hesitation off idle. It had a huge one but after resizing the idle air tubes Im 95% happy with it. I also rejetted the center carb. I have found that each rebuild kit seems to be a bit different and after I rebuilt the center carb and end carbs, it took 2 years and at least 40 times, changing carbs, using different kits, modifying, I finally have what seems to work. I also experienced the slow closing but after messing with the center carb, I no longer have this problem?. Im sure glad its finally fixed and wish I knew what exactly cured my problems. Last thing I did was dill out the idle air tubes a bit more and install a different power valve. It went from not driveable to as good as any carbed car. Oh and I also made some block off plates and then installed just the front and rear base plates. I lost vacuum with each one installed. Im a firm believer that it is impossible to not have a small amount of vacuum leaks at the front and rear. The surfaces are not that smooth from the factory and you need clearance between the throttle plates and the base or you would bind. The Vintage speed ones had as much gap as my factory plates and also showed vacuum drops when installed. I think that its all in the tune of the center carb to make it all work right and to keep the vacuum leaks on the end carbs to a minimum. You cant spop the leaks 100%

[cjaghblb]

Yes those are .030, actually .031 now as one was at .030 and the other was at .031 so I made them both the same. I used whats my drill kit calls a #68 wire gauge size drill and I used my micrometer to verify the size, now at .031 (bothered to calibrate it and everything). My micrometer and my vernier calipers both have inch to thousandths printed on them and they says 1/32 of an inch = .0312 so its pretty much a 32nd of an inch across

[Dick Boneske]

I agree with the last few posts. No matter how well the throttle plates fit and how tight the throttle shafts are, there will be air leakage through both end carbs. When reconditioning the end carb bases, we always try to tweak the throttle plate positions for minimum clearance. If this can't be done due to wear or corrosion of the plates or throttle body, DAG works well to improve the seal. As I've posted before, the three NOS end carbs I have all have DAG on the throttle plates from the factory.

I also use blockoff plates for the end carbs to make sure the center carb performs well at idle and off idle. I have NEVER seen a Tripower setup, however, where the center carb settings (idle speed and air bleed screws) remained the same with and without the blockoff plates. Idle speed goes up and idle mixture gets leaner with the blockoff plates removed due to air leakage on the end carbs.

I looked through about 14 end carbs of various years. The end carb throttle plates had holes ONLY on the '64 and newer end carbs. All the '59-'63 end carbs I looked at have do not have holes in the throttle plates. The ones with holes measured 1/32".

On the large based Rochester 2 bbl. carbs (non-tripower) I have, the holes in the throttle plates are .116". I found two carbs on my '66 Tripower center carbs where someone brazed the holes shut. This .116" size must have been determined by Pontiac to be the approximate amount the end carbs leak air.

I, too, have tried to buy smaller quantities of DAG 213. The manufacturer will not sell small quantities. I have an 20+ year old one pint can of it, which should last as long as I live.

We still don't have an answer or good guess of why Pontiac added the .030" holes in the end carb throttle plates!! One clue I can give you is that they have nothing to do with throttle plates hanging open due to vacuum as some posters have suggested.