73 Riviera General Engine Questions

[73rivi]

Hey everyone, I've got 2 questions.

I've got a stock 1973 Riviera.

First, I'm running with the stock 4 bbl Rochester carb with the thermostatic choke in the manifold. Just bought the car 2 years ago, and it seems as though the choke coil is on its last leg. I would prefer to get a new thermostatic coil, but I've been having a hard time locating one. Would it be better to upgrade to and electric choke? Any leads on where to find a thermostatic choke?

Second, when I stomp on the gas, it seems as though the engine bogs down, and then it'll take off. I'm assuming this is the fuel pump. If so, would it be ANY advantage to get a pump from a stage 1 with a larger reservoir, as opposed to just replacing it with a stock 455 fuel pump?

Any help with either of these would be greatly appreciated.

[JalopyBob]

That bog is just "quadrajet bog" more than likely. Chances are that the fuel pump is not the culprit. First check the timing. 73 was towards the beginning of EPA restrictions, and your 455 is a somewhat detuned version of the real deal. Most of the time it will run better if advanced slightly from the factory spec. Next check your vacuum lines. Next step would be to check for carb adjustment. Are you running premium fuel? The 73 was a great highway car, and with stock exhaust if you drop it down into passing gear at about 60-65 it sounds really good.

[NTX5467]

The "divorced" choke coil you reference might be available through NAPA stores. Borg-Warner used to still service those well after GM Parts discontinued them. You might also check www.RockAuto.com for some part number referenced.

(A "divorced" choke is where the choke thermostatic coil is mounted on the intake manifold, on top of where the exhaust heat crossover is in the middle of the manifold. An "integral" choke is where the thermostatic coil is mounted on the side of the carburetor with no external linkages between the choke coil and the linkage that runs the choke valve open or closed.)

There is no factory electric divorced choke setup for GM vehicles. In that same general time frame, Chrysler had some "electric assist" divorced chokes which had a ceramic heating element mounted beside the divorced choke thermostatic coil--with a timer and such to run the electric part. When GM started using electric assist chokes, it was in the middle 1980s as by that time, all of the QJet chokes were "integral" chokes. If your carb had an integral choke coil, then it might be easy to replace the existing choke coil with one that has the electric heater in it, but then you'd need a way of modulating and controlling the electricity to the choke (Holley has some of those things in their catalog, which would simplify that particular addition to the integral choke QJet).

The "bog", if it's when you "air out the secondaries", could be from the 2.25" secondaries' air valve opening too quickly. It's controlled by two items--the spring on air valve shaft itself and also by the choke's (front, if there are two of them) vacuum break. If the air valve tension spring is too loose AND/OR the hole in the nipple on the vacuum break is too big, it'll let the secondary air valve open too far too quickly.

You might manually (with the engine NOT running) open the air valve for the secondaries. Make sure the hanger for the metering rods for the secondaries ALSO raise as the valve opens. If the hanger does not raise, the plastic cam that does the raising could be worn or "gone". There's also an Allen screw on the lower part of the passenger side air horn housing and an adjusting screw to adjust (wind-up) the secondary air valve spring . . . with a particular tension specified in the factory service manual (usually). This should be right where the secondary air valve shaft goes through that housing . . . NOT where the bottom secondary throttle plates are. The actual secondary throttle plates are openned manually by the linkage on the driver's side of the carb, at "an amount" that's nailed down by the carb's throttle linkage (i.e., not adjustable), but how much air actually goes through the secondaries is controlled/modulated by the upper air valve (which is controlled by the spring tension and vacuum break items).

As for the fuel pump, the issue you describe is just the opposite of the way a "low capacity" or "low output" fuel pump would act. If it ran "out of gas" at the top of Low gear at WOT, that would be a fuel supply issue rather than a lower speed bog.

Also, with the engine NOT running, move the throttle linkage at the carb to check for accelerator pump "shot" into the primaries. It should be solid and strong.

Just some thoughts,

NTX5467