[Tubolare Zagato]

While i was rebuilding my DCOE32s i measured the accelerator pump's rod stroke and i found it to be around 12.3 mm.
What are your measurements?

Also while i tested the accelerator pumps i found out that one barrel is squirting a bit less fuel that the other, in both cars. I check it by recording the distance at where the fuel reaches. May i assume that this is normal?

 

[101 Alfa Mike]

Common sizes are 10 mm (59.5 mm overall) and 14 mm (63.5 mm overall). Longer rods are available and, of course, yours may have been ground to an intermediate length.

 

[Tubolare Zagato]

Thank you!
Something about the difference in squirting distance?

 

[101 Alfa Mike]

The accel jets are quite small and easily plugged and the springs tend to fatigue with time. Suggest you swap parts back and forth until you find the culprit.

 

[Alleggerita]

Apart from something being plugged, also check the pump exhaust jet (or whatever it is called), as it also influences overall fuel volume.

 

[papajam]

...also check the pump exhaust jet (or whatever it is called),...

Also known as the pump bleed.

 

[Tubolare Zagato]

Thanks guys, i will check and let you know!

Is there any way to measure the volume of squirt(s)?
This could directly drive me to the cause of the problem.
If the volume is the same, then the cause is plugged jets.
If the volume is different then someone should take a look at the bleed valve or ball/weight areas.

 

[101 Alfa Mike]

Sure. Pull the carbs off and do a bench test. You should expect something in the range of 0.20-0.25 cc/stroke.

IMO, "squirt time" is every bit as important. I had a data logging system on my spider and could see the A/F ratio go rich after about 1 second.

 

[bearbvd]

Pump circuit tuning

Lots of folks don't understand that the pump jets also serve as a high speed bleed that influences (richens) the far top end of the main circuit. The weight (size thereof) sitting on top of the ball, in combination with the size of the choke, controls when the bleed starts.

As far as the pump stroke--unless you are NOT getting enough squirt volume with the pump return jet down to zero, you do NOT need a longer pump rod.

Once the size of the pump jets (and the weights) are correct for the MAIN circuit, leave them ALONE.

The way to increase the RATE of pump squirt through a given pump jet is to go to a stiffer (or softer) pump SPRING--there are at least five different ones available, Alfa generally used the softest one in its stock settings.

The way to shorten (or lengthen) the length of time the squirt continues is by adjusting the size of the pump return jet (larger=shorter squirt, smaller=longer squirt).

If you have a squirt that gives you good, but not too rich, immediate response, but the squirt doesn't last long enough (you get a lean hesitation AFTER good initial response, then the return jet is too large. On the other hand, if you get a rich spot (puff of carbon) after a good initial response, the return jet is too small.

FINALLY--if taking the return jet down to zero doesn't cure a (delayed) lean hesitation, it's time to go to a longer pump stroke, and work back down from perhaps a .70 pump return jet until things are right.

Absolute waste of time to play with the length of the pump rod otherwise.

Greg

 

[101 Alfa Mike]

Near as I can tell, the pump weight only comes from the parts bin in one size. How do you modify it? Just grind down the diameter? Length? Is this really sensitive? Or is major grinding needed to make a noticable difference?

Running a closed return jet with the weakest springs gives an overly long squirt time. Otoh, going up even one step in spring stiffness gives about 2x the spring pressure.

Mike R

 

[bearbvd]

Pump circuit stuff--

Yep, the pump valve weight only comes in one size.

Grinding the non-ball end is the place to adjust the weight.

I suppose if one needed MORE weight (giving a later cut-in of the top end bleed), a heavier weight could be made, from a tungsten alloy, if necessary due to space limitations.

In general, bigger chokes will reduce the amount of depression this circuit sees at the top end, so need for a heavier weight is unlikely. Nope, I can't imagine anyone wanting to go to smaller chokes than what Alfa used stock !!

You need a balance that will weigh to .1 gram to get them all the same within an appropriate tolerance.

I have generally found the third spring from the softest and .40 pump jets to be a good starting place when working with large chokes.

If there is a bit of a lean spot around 5500 rpm, lightening the weights can be a good way to try to fill it in.

(Assuming you are ALREADY running 1.75 or 2.00 inlet valves ---having the fuel level in the bowls drop slowly while you are testing leads to WEIRD results !!!)

Greg