FAQ

 

  1. Will a tripower bolt onto my 455 with 6X heads?
  2. I am putting a tripower on my 78 Trans AM and the waterneck hits the timing chain cover. What is wrong?
  3. I put a tripower on my 66 GTO that came with a 4 barrel. My throttlecable bracket bolts to the intake just fine, but the cable will not give me full throttle. What is wrong?
  4. My tripower leaks fuel out of the throttleshafts. Where can I buy new shafts and where can I get bushings installed in the throttleplate?
  5. My tripower leaks fuel. Sometimes it pours out of the top and I have to remove the airhorn because the float is stuck. Other times, it drips off the end of the throttleshaft. The car is hard to start and blows black smoke. What is wrong?
  6. I heard you carry a replacement for the needle/seat. Can you tell me aboout it? I don't really get this question, but put it in so I could answer it.
  7. Will an HEI fit on a Pontiac with a tripower?
  8. What is the CFM of a tripower?
  9. Is a tripower better than a four barrel?
  10. I need a 1964 trpower front carb # 7024178 for my 64 GTO with automatic transmission. Do you have one you would sell?
  11. I am running a 455 with an 041 cam.  At idle my center carb drips fuel, making the car run rich.  What is wrong?                     

 

First, a 455 has the same deck heigth as the 326, 350, 389, 400, 421, and 428. That said, the head is the critical factor. Heads from 61 to 64 have different water passages, a different bolt pattern, and a different angle where they meet the intake than do the 65 and later heads.

Therefore, what most people want is the popular 65 or 66 tripower to fit the improved and readily available 65 up heads. A 65 or 66 tripower will bolt directly to the 65 to 71 Pontiac heads. However, starting in 72, Pontiac has an extra exhaust crossover port in one of the heads. The 6X head is a mid-70s head and has this extra port. The 65/66 intake will not cover this port. There is no special intake gasket to accomplish this. The force of the exhaust is too intense for a gasket to stop. Best method is to have a machine shop fill this extra port while you are having the head work done. At least one customer filed this port while the head was on the car, using JB Weldand reports no problems. I am much more comfortable with the first method.

2) I am putting a tripower on my 78 Trans AM and the waterneck hits the timing chain cover. What is wrong?

Note that the waterneck on a tripower comes directly out of the front of the intake, compared to the top location for the thermostat on the 2 and four barrel intakes. Pontiac cast an indentation into the aluminum timing chain covers. I am not sure when this began, but I imagine it was as early as the first 389s in 59. In any case, Pontiac continued using the same castings for this cover until about 69. I have been told that a bit of grinding on the timing chain cover as well as a bit on the waterneck will make it fit. I recommend using the older style timing chain cover, though. Be aware that Pontiac used a different style waterpump after 1967. Make sure you brackets for the alternator, waterpump and airconditioning come off motor with the same style waterpump.

Also, do not assume your 65 motor has a 65 timing chain cover. The covers are interchangeable. I had a 65 timing chain cover on a 70 model 455. No problems.

3) I put a tripower on my 66 GTO that came with a 4 barrel. My throttlecable bracket bolts to the intake just fine, but the cable will not give me full throttle. What is wrong?

There is a differnece in the lengths of each throttle cable. The two bbl cars, four bbl cars and tripowers cars had different cables and different brackets. If you can locate a brakcet and a cable off, say a 66 LaMans with a 2 bbl, it will work on the tripower.

You can make some adjustments in the bracket by either elongating the two mounting holes and/or altering the opening in the bracket that accommodates the flare in the end of the cable.

I carry, as do other suppliers, a reproduction tripower throttle cable bracket. However, I am not confident it will work perfectly with the 4 bbl cable. Some suppliers carry a reproduction throttle cable. It is rather generic, as it has several holes in the end to attach to the center carb. It would not be suitable for a "correct" car, but would work well on a driver. In any case, the tripower reproduction bracket will come closer to the mark than the 4bbl bracket. If you have experience with this, e-mail me and I will add information to this section.

4) My tripower leaks fuel out of the throttleshafts. Where can I buy new shafts and where can I get bushings installed in the throttleplate?



You are not approaching this from the correct perspective. First, fuel should never sit on top of the butterflies which is what is happening here. The problem is not your shafts, but the source of the fuel. See my answer to the next question for more information

Regarding new bushings in the throttleplate....People who are familiar with the Quadrajets often pass along this advice. The Quadrajets have aluminum throttleplates which do wear out. Then, they leak air, essentially a vacuum leak that effects idle quality. Rochester 2 bbls have cast iron throttleplates that seldom wear out. The shafts are usually brass, Nickel plated.  I replace about 50% of the center shafts I inspect.  End carb shafts are not usually as effected, but I am replacing about 20% of those I inspect.

New throttleshafts are available in the shopping cart.

 

5) My tripower leaks fuel. Sometimes it pours out of the top and I have to remove the airhorn because the float is stuck. Other times, it drips off the end of the throttleshaft. The car is hard to start and blows black smoke. What is wrong?

In the last year or so, I have been getting this question all too often.  I discovered that this new Ethanol fuel has a 20 degree lower boiling point than gasoline of the past  I believe that heat from the exhaust crossover is boiling the fuel out of the center carb.  End carbs may also be involved. Anything to cool the carbs, especially after engine is shut off should help.  Possibly a radiator fan on a thermostat controlled swith that runs even after ignition is off.  Or, blocking at least one side of the crossover, or Phenolic spacers under the carbs.

Boy, this is a problem that I get many e-mails about. There are many factors that contribute to these problems. First, you need to rule out dirt or rust getting into the carbs from the fuel system.

Here are several other items to check:

excessive fuel pressure......Common problem when first installing a tripower. These Rochester carbs can only withstand 3 to 4 pounds of fuel pressure. I had one customer who insisted he could not have fuel pressure problems because he had a replacemnet pump he bought at a discount auto parts store. After fighting the problem for several weeks, he checked the pressure......8#.  High pressure does not equate to a good pump, but poor quality control on the part of the manufacturer. There is a relief valve in the pump that controls excessive pressure. Get a good quality regulator and a gauge and set pressure at 3 1/2#

float is sticking......This typically will not happen if you have no debris in the fuel system. However, you may experience it within the first few days of getting you car running with the new tripower installed. Usually, you do not see the debris that makes the float stick. By the time you remove the airhorn and turn it over to inspect it, the particle has fallen out. Once, I did find what was causing needle to stick open. A very small sliver of rubber hose has fallen off as I forced the ruber hose over the fuel inlet line. It ended up in the front carb. Do not tap or hammer on the airhorn to "break the float loose." Many tripower carbs have scars from backyard mechanics with the hammer mentality. Respect these carbs. They don't make them anymore

faulty floats that leak......brass floats can and do develop leaks and fill with fuel. This is checked easily by removing the float and examining it to see if fuel is inside. If not, submurge in near boiling water.  If leaking, they will bubble profusly!  Composition floats can absorb fuel and become too heavy. I don't think this happens often. I prefer brass floats.  However, they have been discontinued by all suppliers as far as I know.  Re-use your brass floats if they are not leaking.

floats need adjustment.......floats do not just change adjustment while on the car. If your car was fine with no leaks earlier, it is not the adjustment. Typically, the end carbs are set at 23/32" from carb airhorn gasket to seam on brass float, with 1 24/32" drop. Center carbs are 21/32" and same drop, 1 24/32"  These measurements are slightly different from factory specs.  However, they will result in a bit less fuel in the bowls at all times.  I prefer this as it keeps fuel away from the airhorn gaskets and reduces seepage.

loose seat (check this out first!!).............I have run into this many times, especially if the carbs have been rebuilt recently. The seats can loosen in which case you will have a flow of fuel into the floatbowl whenever the motor is running, causing major flooding. The seats are not easily tightened as most have a slot for a very wide tipped screwdriver across the top. Unless you have the correct screwdriver, it is very difficult to tighten the seats adeqately.

needle/seat leaking.........    It is possible that you could have a worn out needle/seat. However, unless your carbs are very old, I doubt this is the problem. See question #6 for information on an improved replacement for the needle/seat.

 

6) I heard you carry a replacement for the needle/seat. Can you tell me aboout it? I don't really get this question, but put it in so I could answer it.

Glad you asked. I carry a valve that replaces the old needle/seat and does a better job of regualting fuel. It will not stick as easily, especially after the car has been sitting for long periods. Sometimes the needle/seat will stick in this situation, while this valve won't. Also, this valve can be installed with a 5/16" socket wrench. Consequently, it can be tightened more easily and is therefore, not prone to coming loose.

7) Will an HEI fit on a Pontiac with a tripower?

The tripower intake extends further back toward the distributor than the 2 or 4 barrel intake to accommodate the rear carb. As a result, an HEI distributor will not fit. I have been told that some material can be removed from the back of the intake and some from the HEI unit and it can fit. I would not recommend it.

There are indivviduals who will convert the points distributor to an HEI unit.  I do recommend Dave at www.davessmallbodyheis.com.  Many of my customers have worked with Dave and give me positive feedback.

My own car actually turned its fastest time with the stock single point distributor, a 12.7 second quarter. I have since added electronic breaker for reliability.

8) What is the CFM of a tripower?

If you read this carefully, you will be surprized. And, you may learn a few things. I did as I did research to find the "real" answer to this question.

First, you must understand that flow numbers are estimates based on a mythical engine. Picture a 400 cubic inch engine running at full throttle. It is essentially sucking air through the venturi of the carb (or carbs). If this engine had a 2 barrel carb, the suction through each venturi would be greater than the suction through each venturi of a 4 barrel. The increased suction would actually increase the flow through each venturi. True, the 4 barrel would produce more CFM flow, but each barrel of the four barrel would produce less CFM than each barrel of the 2 barrel. Right?

Because of this, flow numbers based on venturi diameter have to be adjusted between the four barrel and the two barrel. The error many make is merely to apply a multiple to the four barrel numbers to yield flow numbers for the 2 barrel, then add the numbers up for three two barrels. This doesn't work. Why? Well, now, instead we are working with six open venturi, not two.

The flow numbers on Rochester 2 bbls are measured differently than a 4 bbl. Flow on 2 bbls is measured a 3" drop, while 4 bbls are measured at 1 1/2" drop. To make the numbers comparable, you must divide the 2 bbl flow numbers by 1.414. However, to convert to, essentially, 6 barrel numbers, you need to divide the two barrel flow numbers by ?. Doing so yields the following flow numbers for the various venturi sizes at each measurement.

venturi size 3" (2bbl) 1.5" (4bbl) 1" (tripower-6bbl)
1 3/16" 353 cfm 249 ?
1 1/4" 381 269 ?
1 5/16" 423 299 ?
1 3/8" 435 308 ?

In order to figure the cfm, you need to add up the cfm of each carb.

The 59 to 66 tripower end carbs have a 1 3/8" venturi. Center carbs of 64-65 tripowers have 1 1/4" venturi. Center carb for 66 tripower have 1 3/16" venturi.

Examine the above numbers. These are actual measurements I have taken. Note the difference between 65 and 66 center carbs. This is not a misprint.

I realize the throttle bore diameter is larger on the 66 center carb (1 11/16") than the 64-65 center (1 7/16') However, the venturi, which is the smallest diameter opening in each carb is actually larger in the earlier carb. I told you careful reading would yield surprizes.

CFM figures are not as meaningful as quarter mile numbers. Read answer to question 9.

9) Is a tripower better than a four barrel?

I take my information from the June 1995 issue of High Performance Pontiac. The article is entitled, "Four Barrel vs. Tri-power." The authors employed the services of Jim Taylor to assist. They took a well performing 68 GTO, 428 car, 4 speed with slicks. All launches were made at 1200 rpm and shifts at 5200. Car went throught the traps at 5400-5500 rpm.

The Q-Jet had was dialed in on the car. It was equipted with Edelbrock jets, rods, and high-flow needles. In other words, this carb was modified slightly to match the needs of the car.

The 66 tripower was stock except that the choke plate in the center carb was removed and the jets were replaced with 70s in the center and 72s in the ends.

Three runs were made with each set-up. Results:

- Q-Jet tripower
run 1 13.28/101.7 12.93/103.9
run 2 13.33/101.5 12.92/103.8
run 3 13.29/101.8 12.89/104.1
AVERAGE 13.30/101.66 12.89/103.93

The author calculates the 2.27 mph gain to a 22 hp gain over the 4 bbl. He attributes the gain to the tripower's shorter and straighter intake runners and its greater CFM flow.

10) I need a 1964 trpower front carb # 7024178 for my 64 GTO with automatic transmission. Do you have one you would sell?

Rochester did not start putting carb numbers on the 2 bbls until 1968. The numbers you find in restoration guides only appear on the carb tags attached to one of the airhorn screws.

Often people e-mail me giving me "carb numbers" that appear in a circle on the passenger side of the floatbowl section. These are casting numbers for the floatbowl section. Rochester used the same casting for several carbs, then machined them for specific applications.

There is one exception to this rule. If you bought a new Rochester carb at the dealer after 1968, Rochester DID stamp the carb number onto the passenger side of the floatbowl, horizontally. I have only seen 2 or 3 of these carbs in many years of restoring tripowers. Another diffenece I have noted about these carbs is that they also have phillips head screws holding down the airhorn.

So, since numbers non most tripower carbs only appear on the tags, and tags can be easily switched, beware. The only way to identify a tripower carb is visually. This really isn't too difficult after looking at these carbs and working on them for several years. However, if you are not familiar with how to identify them, learn before buying a unit.

11) I am running a 455 with an 041 cam.  At idle my center carb drips fuel, making the car run rich.  What is wrong?