67 tri-power secondary carb --jets???

[Fred Y.]

I have recently brought my 67 400 hp car to have it dyno'd.The shop saw a hugh drop in power from "excesss" fuel being dumped in the secondary carbs when they were open @ 4300 RPM.The shop wanted to know what the correct secondary jets were. I told them my 67 shop manual states #64 for the primary's & .076 for the secondary's.I wanted to have a look at what I have in my secondarys today ,so I removed the front bowl to have a look & I find no secondary jets.I'd appreciate some help here before I reassemble the front bowl.Thanks in advance.

[Wayne M.]

Re: 67 tri-power secondary carb --jets???

I have recently brought my 67 400 hp car to have it dyno'd...... I find no secondary jets.I'd appreciate some help here before I reassemble the front bowl..

The tripower set-ups have NO jets in the front and rear List 3659 carbs --- just metering plates. Don't believe there's any adjustment there, but other gurus will jump in with more details.

[Fred Y.]

Re: 67 tri-power secondary carb --jets???

Thankyou Wayne,I'll see what other info I can find out.

[Howard P.]

Re: 67 tri-power secondary carb --jets???

You may wish to explore the Holley website as numerous metering plates use to be available to fit these carbs. If you feel adventurous a company called AED makes a conversion metering plate which will accommodate the Holley jets as used in the centre carb. Should you chooseto go this route be prepared to either modify or replace your floats.

The results are worth the time spent. Good luck

[Fred Y.]

Re: 67 tri-power secondary carb --jets???

Thanks Howard,
I'll keep looking into this.

[Clem Z.]

Re: 67 tri-power secondary carb --jets???

remove the plates and use a .076 drill bit to check to make sure no one drilled them over size.

[Fred Y.]

Re: 67 tri-power secondary carb --jets???

Will do-Thanks!---Also, I have learned on the holley site that various springs can be purchased to speed-up/slow down the opening time of the vacume secondarys------could be the solution!

[Fred Y.]

Re: 67 tri-power secondary carb --jets???PROBLEM SOLVED!!

Just a note to let those viewing & giving suggestions,especially Clem! I removed the metering blocks & found that the metering blocks had been drilled out far beyound the original .076 diameter!As a matter of fact,closer to .086-(way too much gas). A gentleman in Fla. by the name of Craig(really helpful) sent me 2 new plates w/ gaskets etc. & she's running great now @ the upper RPM's .
Now,I need to have a closer look @ the final adjustments for my primary carb.Does anyone recall the correct procedure for tuning the two idle adjuster screws??I am hearing a slight popping noise out the right sidepipe ocassionally (and only) when she's been idling for as few minutes.But she's definetely not running as smooth as she should now @ idle & I believe it is a bit too lean!But,I'm not positive ,so I'd appreciate the imput.
Thankyou!

[John H.]

Re: 67 tri-power secondary carb --jets???PROBLEM SOLVED!!

Now,I need to have a closer look @ the final adjustments for my primary carb.Does anyone recall the correct procedure for tuning the two idle adjuster screws??

Connect your vacuum gauge to a full manifold vacuum source (the fitting on the intake just below the secondary diaphragm on the rear carb, the PCV hose port on the intake below the center carb, or the choke pull-off diaphragm hose on the center carb), and with the engine at normal idle, adjust the idle mixture screws (alternating back and forth between both sides) to achieve highest steady vacuum, making idle SPEED adjustments as necessary to maintain normal idle rpm.

[Fred Y.]

Re: 67 tri-power secondary carb --jets???

Thanks very much John!

[Jack H.]

Re: 67 tri-power secondary carb --jets???

This may NOT be your problem, but we fought similar symptoms here in Denver with tri-power cars from various years ('67-69). Essentially, the engines would fall on their faces when pushed to +5000 RPM, but run nicely below that level...

After verifying the carbs, their installation, the spark system, cam profile and just about everything else we could think of, we rented time on a chassis dyno. We were able to recreate the 'problem' and with the car instrumented (exhaust sniff + ignition waveform monitor), we observed over rich emissions tail pipe emissions when the engine stumbled...

Finally, we instrumented the carbs with a video monitor and re-ran the test. We saw random spurts of raw gas errupting from the vent stacks of all three carbs with the fuel being sucked into the venturi's of the carbs.

We soaked shop towels in water and cooled them in a refigerator freezer then wrapped the fuel lines from the pump to each carb and re-ran tests. The engine climbed EFFORTLESS to its red line UNTIL sufficient underhood heat warmed the shop towels...

We emptied the gas tank of its pump gas (doped with ethanol at approximately 10%) and laid in pure race gas. Once the pump gas was purged from the lines/carbs, the engine ran to red line without a hiccup EVERY time!

We concluded that today's alcohol doped pump gas + our altitude had reduced the fuel's boiling point crossing the original design safety margin line of the tri-power setup's thermal dissipation limits. We've seen no similar problems with conventional single 4-Bbl carb engines....

[Clem Z.]

Re: 67 tri-power secondary carb --jets???

the nitrophyl floats have a shorter fulcrum arm to clear the jet plate used in the F&R carbs on the 3 X 2 setup than the brass floats so they do not exert as much pressure on the needle/seat as the brass floats do. also i always blocked the heat riser crossover passage in the intake and installed a hot oil splash shield in the tappet chamber to cover the whole bottom of the intake manifold to reduce the intake manifold temp

[Fred Y.]

Re: 67 tri-power secondary carb --jets???

Jack-Thanks for your input. I did find several other things.
#1) I found that the upper "squirter"or pump shot @ top of the carb that shoots fuel in during initial pedal was only shooting from one of the two nozels.Replacing that with a new one helped greatly for throttle response.
#2) I re-tuned the idle needle valves on the primary @ 3 1/4 turns out on each which gave me a vacume of 13.5 in @ 8-9 hundred rpm idle.
#3)Lastly,& perhaps most importantly(I should post this for other members) the elec.limited electronic "vanes on my module for my distributor were rubbing against the centrifucal advance shaft/slot under the upper cam where it is attached.Tightening down the vanes from the bottom up with the supplied screws caused the advance to NOT fully retard when you got off the pedal.Starting the car with a semi-advanced distributor was not happening & I simply solved the issue by grinding away sufficient metal from the vane plate to clear the advance slot under the upper dist. cam.-now the advance return springs were able to pull the parts back to the fully retarted position.
The car seems to be happy now! & in case you didn't see my other post,I found out the backfiring @ higher RPM's came from some intelect who decided to drill out the .076 jets in my secondary metering blocks from .076 to approx .086---------too much gas!!