I am thinking of going to a Tri-Power setup in my 72. Right now I have a 427 390Hp and I use my return fuel line and also my PCV system with the canister it originally came with. My questions are what do I do with the return fuel line? Cap it off? And what do I do with my current PCV system with the canister, I would like to keep it if possible just not sure how I would hook it up.

Thanks for the help,

Joey

 

There is no problem running a PCV on the Tripower - the Tripower system has a PCV hose attachment port. Just hook it up. Running a vapor canister is a different problem, because the Purge Valve on the '72 Evap system requires a ported vacuum source to trigger the purge valve operation to make the system work. The Tripowers I have worked on do not have a ported vacuum port. Check the vacuum ports on your center carb to see if you have ported or manifold vacuum on the vacuum nipple. If, by chance, you have ported vacuum, you can "T" into that line and use it for your purge valve trigger vacuum. But if it's manifold vacuum, you can't use it: It will allow the can to be purged at all times (including at idle), which will have the effect of a significant vacuum leak at idle.

For fuel return, just use a fuel pump with a fuel return port on it, like the stock '72 pump, and hook up your stock '72 return line Your other option is to use the '68-style small block in-line filter with the fuel return, and run the return line from the filter down to your return line on the frame.

Lars

 

Thanks Lars. Makes sense. Here are the 2 ports in the center carb. One is in base plate. I am not sure which is manifold or ported vacuum.

Joey

 

The small one (upper) is for the Secondaries and won't be appropriate for the purge source.

 

I do have a spare center carb. that I can look at this weekend to see if the one on the Base Plate is ported or not. (someone else will probably answer sooner though)

 

The nipple in the baseplate is almost always manifold vacuum. The nipple in the center of the carb is venturi vacuum to operate the secondaries, and cannot be used as a purge valve trigger. If you flip the center carb upside-down and look up the throttle bore, you should be able to see if it even has a slotted opening just above the forward edge of the throttle plates for ported vacuum. If it does, you can trace that circuit down and see if it would be practical to drill an intersection hole into that passage in the float bowl or the metering block.

Typical ported vacuum slot in the throttle bore just above the level of the forward edge of the throttle plates when the plates are closed at idle:


If you cannot locate, or create, a ported vacuum source, you cannot use the purge canister unless you changed it over to a late-model ECM-controlled canister with a solenoid-actuated purge valve. You could trigger the purge valve using a throttle position switch to assure that the purge valve only opens when the engine is above idle.

Lars

 

Looks like both ports will not work after checking. Can I just not use the canister if I plug the line going to it from the tank and then adding a vented gas cap?

Joey

 

Yes. But California politicians and Alexandria won't like you. Trade the Vette in on a Leaf.