The following subtopics are discussed in this article -
To get an engine to accelerate smoothly, you need both an increase in the timing (advance the timing) and an increase in fuel flow.
The vacuum distributor senses when you open the throttle and provides the extra advance timing.
When you open the throttle, the airflow increases immediately but the fuel (being denser) takes a moment to catch up with the increased airflow. This would result in a lean mixture for a few moments (the car would hesitate), so the carburetor has an accelerator pump built into the side of it which supplies a shot of fuel to ensure smooth acceleration. The accelerator pump connected by a linkage to the accelerator; when acceleration is required, the pump squirts a spray of fuel directly into the throat of the carburetor to momentarily increase the fuel-to-air concentration. You can see it operate if you pull the air cleaner off and look down the carburetor throat.
There is a small bent brass pipe right pointing right straight down the throat of the carburetor-- this it the delivery tube. Grab the throttle arm and pull it firmly (like you were pushing down on the accelerator). You should see a squirt of fuel from the delivery tube straight down the throat of the carburetor.
Now if you pull on the throttle arm very slowly you'll see that the accelerator pump does nothing - no squirt. It's set that way because when you open the throttle slowly the fuel flow has time to keep up with the increasing airflow - not extra shot of fuel is necessary.
An inherent problem with the 009 centrifugal-advance distributor is that it has an acceleration 'flat spot; that is, it hesitates on acceleration at low speeds. One thing that may compensate for this is to adjust the accelerator pump for maximum stroke. This is done as follows:
The 34 PICT/3 carburetor has a bell-crank with an adjusting segment (see the exploded figure in Section 2.1.2, "Disassembly and Cleaning"). The quantity of gasoline that is injected upon acceleration can be measured. With the float bowl filled with fuel, attach a length of tubing to the discharge end of the accelerator pump injector so that the expelled gasoline can be caught and measured in a 25-ml graduated cylinder. Hold the graduate under the end of the tubing and operate the throttle valve rapidly exactly ten times. Measure the amount of gasoline caught and divide by ten to get the average quantity of a single injection pulse. The average quantity should be 1.45 to 1.75 ml for the 34-PICT/3 carburetor.
To adjust the injection quantity, loosen the retaining screw and turn the adjusting segment clockwise to decrease injection quantity or counterclockwise to increase the injection quantity. Then tighten the retaining screw and recheck the injection quantity.
NOTE: To compensate for the flat spot inherent in the 009 distributor, adjust the accelerator pump injection quantity to the maximum; i.e., move the adjusting segment counterclockwise as far as it will go.
On our 1971 1600tp engine (34PICT/3 carburetor and alternator) we found that the accelerator pump linkage was impinging on the alternator in two places -- the accelerator pump adjustment screw, and immediately forward of the accelerator pump itself. We couldn't see the latter interference readily because of the air cleaner and the automatic choke. This interference was preventing the idle screw from touching the choke cam like it's supposed to, thus making it impossible to properly tune the carburetor.
This interference was puzzling to us and remains so -- the manifold is positioned by the heat riser being one piece, yet the alternator was designed to fit.
Rob suggested that we raise the carburetor so that the accelerator pump linkage would clear the alternator. He wrote -
It would be a very simple job for a workshop to make a spacer out of brass for you (to fit under the carburetor to raise it up). You'd just need to take one of the gaskets to them to use as a pattern, and decide how high it needs to be (1/2 inch or so?) Then use a gasket on both sides of the new spacer and you are in business. 2 3 gaskets under the carburetor might be enough, if you can't get a spacer.
Not sure about the bolt length on the carburetor though - you might have to replace the studs with longer ones or use through-bolts. If they currently have a little spare thread under the nut, measure this length and determine whether this thickness spacer would give you enough lift. Even 1/4 inch might do it.
We finally solved the interference problem three ways -- we raised the carburetor a bit with three home-made gaskets, ground a bit off of the adjusting bell and nut, and ground just a titch off of the alternator body.
Disclaimer stuff: Rob and Dave have prepared this information from their own experiences. We have not assumed any specialised mechanical knowledge, but we DO assume that anyone using this information has at least some basic mechanical ability.
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Last revised 4 May 2004.