Customs Cadillac tri power

I would agree with Phil. If possible run the car out on the road and recheck. By the way what are you using for fuel pump pressure?

 

Unfortunately, I do not have the interior in the car, no seats and we got 5" of snow on the roads. I'm using the standard fuel pump, mechanical from the 1960 caddy with 1/4" return line to the new tank.

 

It has been a while since I have played with a 2gc but 5-6 lbs pressure comes to mind. That pump could be overdriving the inlet. When I ran my 348 tri power I switched to Grose units which was recommended by larry Fulton who builds induction systems. Also recommended using a fuel pressure regulator. I am using a Holley regulator with a return line to the tank on my 97's. Also recommeded by Clive at Stromberg.

 

12 inches of vacuum is probably because the center carb is from a 390 and you have a 331, and you have a cam that may be too large for a street engine.

GUESSING you have venturi velocity which is much too low, causing the power circuit to be involved at idle, as well as a mal-functioning idle circuit.

Again GUESSING that you will need to add an idle air bypass to the center carb. This will allow better idle air velocity control, which will enable the idle mixture control screws to work. You may also need to adjust the tension of the spring on the power valve actuating valve. This is a very common O.E. fix for an overcarbed or overcammed engine.

Until at least testing for these issues, I would NOT suggest playing with jets. If I am correct in my guesses, and you lower the jets to get the system to work at idle and low RPM, the engine may go drastically lean at load.

You might find it easier to bore/stroke the 331 to 390 than make the 390 carbs work on the 331

Jon

 

May I add that the combustion chamber is larger on the 390 heads ,when you install these heads on a smaller bore you create a sharp edge into the chamber . This creates uneven combustion which could lead to detonation ! Lay a 331 head gasket on a 390 head you will see head gasket exposed to heat that it's not designed for . I would bore block to 4 inch specs .

 

Idle circuits work and when closed engine dies. opening and adjusting does change the rpm of the motor. Vacuum runs between 10 and 12.

 

If you want to get any kind of fuel economy, do not lock out the vacuum advance.

Have you looked down the carb throat with the engine idling? You shouldn't see any fuel coming from the venturii's or any other place. The whole throat should be dry at idle. If you do see wet spots or fuel dripping, you have something causing a high float condition.